# frozen_string_literal: true module ActiveRecord # See ActiveRecord::Associations::ClassMethods for documentation. module Associations # :nodoc: extend ActiveSupport::Autoload extend ActiveSupport::Concern # These classes will be loaded when associations are created. # So there is no need to eager load them. autoload :Association autoload :SingularAssociation autoload :CollectionAssociation autoload :ForeignAssociation autoload :CollectionProxy autoload :ThroughAssociation module Builder # :nodoc: autoload :Association, "active_record/associations/builder/association" autoload :SingularAssociation, "active_record/associations/builder/singular_association" autoload :CollectionAssociation, "active_record/associations/builder/collection_association" autoload :BelongsTo, "active_record/associations/builder/belongs_to" autoload :HasOne, "active_record/associations/builder/has_one" autoload :HasMany, "active_record/associations/builder/has_many" autoload :HasAndBelongsToMany, "active_record/associations/builder/has_and_belongs_to_many" end eager_autoload do autoload :BelongsToAssociation autoload :BelongsToPolymorphicAssociation autoload :HasManyAssociation autoload :HasManyThroughAssociation autoload :HasOneAssociation autoload :HasOneThroughAssociation autoload :Preloader autoload :JoinDependency autoload :AssociationScope autoload :DisableJoinsAssociationScope autoload :AliasTracker end def self.eager_load! super Preloader.eager_load! JoinDependency.eager_load! end # Returns the association instance for the given name, instantiating it if it doesn't already exist def association(name) # :nodoc: association = association_instance_get(name) if association.nil? unless reflection = self.class._reflect_on_association(name) raise AssociationNotFoundError.new(self, name) end association = reflection.association_class.new(self, reflection) association_instance_set(name, association) end association end def association_cached?(name) # :nodoc: @association_cache.key?(name) end def initialize_dup(*) # :nodoc: @association_cache = {} super end private def init_internals super @association_cache = {} end # Returns the specified association instance if it exists, +nil+ otherwise. def association_instance_get(name) @association_cache[name] end # Set the specified association instance. def association_instance_set(name, association) @association_cache[name] = association end # = Active Record \Associations # # \Associations are a set of macro-like class methods for tying objects together through # foreign keys. They express relationships like "Project has one Project Manager" # or "Project belongs to a Portfolio". Each macro adds a number of methods to the # class which are specialized according to the collection or association symbol and the # options hash. It works much the same way as Ruby's own attr* # methods. # # class Project < ActiveRecord::Base # belongs_to :portfolio # has_one :project_manager # has_many :milestones # has_and_belongs_to_many :categories # end # # The project class now has the following methods (and more) to ease the traversal and # manipulation of its relationships: # # project = Project.first # project.portfolio # project.portfolio = Portfolio.first # project.reload_portfolio # # project.project_manager # project.project_manager = ProjectManager.first # project.reload_project_manager # # project.milestones.empty? # project.milestones.size # project.milestones # project.milestones << Milestone.first # project.milestones.delete(Milestone.first) # project.milestones.destroy(Milestone.first) # project.milestones.find(Milestone.first.id) # project.milestones.build # project.milestones.create # # project.categories.empty? # project.categories.size # project.categories # project.categories << Category.first # project.categories.delete(category1) # project.categories.destroy(category1) # # === A word of warning # # Don't create associations that have the same name as {instance methods}[rdoc-ref:ActiveRecord::Core] of # +ActiveRecord::Base+. Since the association adds a method with that name to # its model, using an association with the same name as one provided by +ActiveRecord::Base+ will override the method inherited through +ActiveRecord::Base+ and will break things. # For instance, +attributes+ and +connection+ would be bad choices for association names, because those names already exist in the list of +ActiveRecord::Base+ instance methods. # # == Auto-generated methods # See also "Instance Public methods" below ( from #belongs_to ) for more details. # # === Singular associations (one-to-one) # | | belongs_to | # generated methods | belongs_to | :polymorphic | has_one # ----------------------------------+------------+--------------+--------- # other | X | X | X # other=(other) | X | X | X # build_other(attributes={}) | X | | X # create_other(attributes={}) | X | | X # create_other!(attributes={}) | X | | X # reload_other | X | X | X # other_changed? | X | X | # other_previously_changed? | X | X | # # === Collection associations (one-to-many / many-to-many) # | | | has_many # generated methods | habtm | has_many | :through # ----------------------------------+-------+----------+---------- # others | X | X | X # others=(other,other,...) | X | X | X # other_ids | X | X | X # other_ids=(id,id,...) | X | X | X # others<< | X | X | X # others.push | X | X | X # others.concat | X | X | X # others.build(attributes={}) | X | X | X # others.create(attributes={}) | X | X | X # others.create!(attributes={}) | X | X | X # others.size | X | X | X # others.length | X | X | X # others.count | X | X | X # others.sum(*args) | X | X | X # others.empty? | X | X | X # others.clear | X | X | X # others.delete(other,other,...) | X | X | X # others.delete_all | X | X | X # others.destroy(other,other,...) | X | X | X # others.destroy_all | X | X | X # others.find(*args) | X | X | X # others.exists? | X | X | X # others.distinct | X | X | X # others.reset | X | X | X # others.reload | X | X | X # # === Overriding generated methods # # Association methods are generated in a module included into the model # class, making overrides easy. The original generated method can thus be # called with +super+: # # class Car < ActiveRecord::Base # belongs_to :owner # belongs_to :old_owner # # def owner=(new_owner) # self.old_owner = self.owner # super # end # end # # The association methods module is included immediately after the # generated attributes methods module, meaning an association will # override the methods for an attribute with the same name. # # == Cardinality and associations # # Active Record associations can be used to describe one-to-one, one-to-many, and many-to-many # relationships between models. Each model uses an association to describe its role in # the relation. The #belongs_to association is always used in the model that has # the foreign key. # # === One-to-one # # Use #has_one in the base, and #belongs_to in the associated model. # # class Employee < ActiveRecord::Base # has_one :office # end # class Office < ActiveRecord::Base # belongs_to :employee # foreign key - employee_id # end # # === One-to-many # # Use #has_many in the base, and #belongs_to in the associated model. # # class Manager < ActiveRecord::Base # has_many :employees # end # class Employee < ActiveRecord::Base # belongs_to :manager # foreign key - manager_id # end # # === Many-to-many # # There are two ways to build a many-to-many relationship. # # The first way uses a #has_many association with the :through option and a join model, so # there are two stages of associations. # # class Assignment < ActiveRecord::Base # belongs_to :programmer # foreign key - programmer_id # belongs_to :project # foreign key - project_id # end # class Programmer < ActiveRecord::Base # has_many :assignments # has_many :projects, through: :assignments # end # class Project < ActiveRecord::Base # has_many :assignments # has_many :programmers, through: :assignments # end # # For the second way, use #has_and_belongs_to_many in both models. This requires a join table # that has no corresponding model or primary key. # # class Programmer < ActiveRecord::Base # has_and_belongs_to_many :projects # foreign keys in the join table # end # class Project < ActiveRecord::Base # has_and_belongs_to_many :programmers # foreign keys in the join table # end # # Choosing which way to build a many-to-many relationship is not always simple. # If you need to work with the relationship model as its own entity, # use #has_many :through. Use #has_and_belongs_to_many when working with legacy schemas or when # you never work directly with the relationship itself. # # == Is it a #belongs_to or #has_one association? # # Both express a 1-1 relationship. The difference is mostly where to place the foreign # key, which goes on the table for the class declaring the #belongs_to relationship. # # class User < ActiveRecord::Base # # I reference an account. # belongs_to :account # end # # class Account < ActiveRecord::Base # # One user references me. # has_one :user # end # # The tables for these classes could look something like: # # CREATE TABLE users ( # id bigint NOT NULL auto_increment, # account_id bigint default NULL, # name varchar default NULL, # PRIMARY KEY (id) # ) # # CREATE TABLE accounts ( # id bigint NOT NULL auto_increment, # name varchar default NULL, # PRIMARY KEY (id) # ) # # == Unsaved objects and associations # # You can manipulate objects and associations before they are saved to the database, but # there is some special behavior you should be aware of, mostly involving the saving of # associated objects. # # You can set the :autosave option on a #has_one, #belongs_to, # #has_many, or #has_and_belongs_to_many association. Setting it # to +true+ will _always_ save the members, whereas setting it to +false+ will # _never_ save the members. More details about :autosave option is available at # AutosaveAssociation. # # === One-to-one associations # # * Assigning an object to a #has_one association automatically saves that object and # the object being replaced (if there is one), in order to update their foreign # keys - except if the parent object is unsaved (new_record? == true). # * If either of these saves fail (due to one of the objects being invalid), an # ActiveRecord::RecordNotSaved exception is raised and the assignment is # cancelled. # * If you wish to assign an object to a #has_one association without saving it, # use the #build_association method (documented below). The object being # replaced will still be saved to update its foreign key. # * Assigning an object to a #belongs_to association does not save the object, since # the foreign key field belongs on the parent. It does not save the parent either. # # === Collections # # * Adding an object to a collection (#has_many or #has_and_belongs_to_many) automatically # saves that object, except if the parent object (the owner of the collection) is not yet # stored in the database. # * If saving any of the objects being added to a collection (via push or similar) # fails, then push returns +false+. # * If saving fails while replacing the collection (via association=), an # ActiveRecord::RecordNotSaved exception is raised and the assignment is # cancelled. # * You can add an object to a collection without automatically saving it by using the # collection.build method (documented below). # * All unsaved (new_record? == true) members of the collection are automatically # saved when the parent is saved. # # == Customizing the query # # \Associations are built from Relation objects, and you can use the Relation syntax # to customize them. For example, to add a condition: # # class Blog < ActiveRecord::Base # has_many :published_posts, -> { where(published: true) }, class_name: 'Post' # end # # Inside the -> { ... } block you can use all of the usual Relation methods. # # === Accessing the owner object # # Sometimes it is useful to have access to the owner object when building the query. The owner # is passed as a parameter to the block. For example, the following association would find all # events that occur on the user's birthday: # # class User < ActiveRecord::Base # has_many :birthday_events, ->(user) { where(starts_on: user.birthday) }, class_name: 'Event' # end # # Note: Joining or eager loading such associations is not possible because # those operations happen before instance creation. Such associations # _can_ be preloaded, but doing so will perform N+1 queries because there # will be a different scope for each record (similar to preloading # polymorphic scopes). # # == Association callbacks # # Similar to the normal callbacks that hook into the life cycle of an Active Record object, # you can also define callbacks that get triggered when you add an object to or remove an # object from an association collection. # # class Firm < ActiveRecord::Base # has_many :clients, # dependent: :destroy, # after_add: :congratulate_client, # after_remove: :log_after_remove # # def congratulate_client(client) # # ... # end # # def log_after_remove(client) # # ... # end # end # # Callbacks can be defined in three ways: # # 1. A symbol that references a method defined on the class with the # associated collection. For example, after_add: :congratulate_client # invokes Firm#congratulate_client(client). # 2. A callable with a signature that accepts both the record with the # associated collection and the record being added or removed. For # example, after_add: ->(firm, client) { ... }. # 3. An object that responds to the callback name. For example, passing # after_add: CallbackObject.new invokes CallbackObject#after_add(firm, # client). # # It's possible to stack callbacks by passing them as an array. Example: # # class CallbackObject # def after_add(firm, client) # firm.log << "after_adding #{client.id}" # end # end # # class Firm < ActiveRecord::Base # has_many :clients, # dependent: :destroy, # after_add: [ # :congratulate_client, # -> (firm, client) { firm.log << "after_adding #{client.id}" }, # CallbackObject.new # ], # after_remove: :log_after_remove # end # # Possible callbacks are: +before_add+, +after_add+, +before_remove+, and +after_remove+. # # If any of the +before_add+ callbacks throw an exception, the object will not be # added to the collection. # # Similarly, if any of the +before_remove+ callbacks throw an exception, the object # will not be removed from the collection. # # Note: To trigger remove callbacks, you must use +destroy+ / +destroy_all+ methods. For example: # # * firm.clients.destroy(client) # * firm.clients.destroy(*clients) # * firm.clients.destroy_all # # +delete+ / +delete_all+ methods like the following do *not* trigger remove callbacks: # # * firm.clients.delete(client) # * firm.clients.delete(*clients) # * firm.clients.delete_all # # == Association extensions # # The proxy objects that control the access to associations can be extended through anonymous # modules. This is especially beneficial for adding new finders, creators, and other # factory-type methods that are only used as part of this association. # # class Account < ActiveRecord::Base # has_many :people do # def find_or_create_by_name(name) # first_name, last_name = name.split(" ", 2) # find_or_create_by(first_name: first_name, last_name: last_name) # end # end # end # # person = Account.first.people.find_or_create_by_name("David Heinemeier Hansson") # person.first_name # => "David" # person.last_name # => "Heinemeier Hansson" # # If you need to share the same extensions between many associations, you can use a named # extension module. # # module FindOrCreateByNameExtension # def find_or_create_by_name(name) # first_name, last_name = name.split(" ", 2) # find_or_create_by(first_name: first_name, last_name: last_name) # end # end # # class Account < ActiveRecord::Base # has_many :people, -> { extending FindOrCreateByNameExtension } # end # # class Company < ActiveRecord::Base # has_many :people, -> { extending FindOrCreateByNameExtension } # end # # Some extensions can only be made to work with knowledge of the association's internals. # Extensions can access relevant state using the following methods (where +items+ is the # name of the association): # # * record.association(:items).owner - Returns the object the association is part of. # * record.association(:items).reflection - Returns the reflection object that describes the association. # * record.association(:items).target - Returns the associated object for #belongs_to and #has_one, or # the collection of associated objects for #has_many and #has_and_belongs_to_many. # # However, inside the actual extension code, you will not have access to the record as # above. In this case, you can access proxy_association. For example, # record.association(:items) and record.items.proxy_association will return # the same object, allowing you to make calls like proxy_association.owner inside # association extensions. # # == Association Join Models # # Has Many associations can be configured with the :through option to use an # explicit join model to retrieve the data. This operates similarly to a # #has_and_belongs_to_many association. The advantage is that you're able to add validations, # callbacks, and extra attributes on the join model. Consider the following schema: # # class Author < ActiveRecord::Base # has_many :authorships # has_many :books, through: :authorships # end # # class Authorship < ActiveRecord::Base # belongs_to :author # belongs_to :book # end # # @author = Author.first # @author.authorships.collect { |a| a.book } # selects all books that the author's authorships belong to # @author.books # selects all books by using the Authorship join model # # You can also go through a #has_many association on the join model: # # class Firm < ActiveRecord::Base # has_many :clients # has_many :invoices, through: :clients # end # # class Client < ActiveRecord::Base # belongs_to :firm # has_many :invoices # end # # class Invoice < ActiveRecord::Base # belongs_to :client # end # # @firm = Firm.first # @firm.clients.flat_map { |c| c.invoices } # select all invoices for all clients of the firm # @firm.invoices # selects all invoices by going through the Client join model # # Similarly you can go through a #has_one association on the join model: # # class Group < ActiveRecord::Base # has_many :users # has_many :avatars, through: :users # end # # class User < ActiveRecord::Base # belongs_to :group # has_one :avatar # end # # class Avatar < ActiveRecord::Base # belongs_to :user # end # # @group = Group.first # @group.users.collect { |u| u.avatar }.compact # select all avatars for all users in the group # @group.avatars # selects all avatars by going through the User join model. # # An important caveat with going through #has_one or #has_many associations on the # join model is that these associations are *read-only*. For example, the following # would not work following the previous example: # # @group.avatars << Avatar.new # this would work if User belonged_to Avatar rather than the other way around # @group.avatars.delete(@group.avatars.last) # so would this # # === Setting Inverses # # If you are using a #belongs_to on the join model, it is a good idea to set the # :inverse_of option on the #belongs_to, which will mean that the following example # works correctly (where tags is a #has_many :through association): # # @post = Post.first # @tag = @post.tags.build name: "ruby" # @tag.save # # The last line ought to save the through record (a Tagging). This will only work if the # :inverse_of is set: # # class Tagging < ActiveRecord::Base # belongs_to :post # belongs_to :tag, inverse_of: :taggings # end # # If you do not set the :inverse_of record, the association will # do its best to match itself up with the correct inverse. Automatic # inverse detection only works on #has_many, #has_one, and # #belongs_to associations. # # :foreign_key and :through options on the associations # will also prevent the association's inverse from being found automatically, # as will a custom scopes in some cases. See further details in the # {Active Record Associations guide}[https://guides.rubyonrails.org/association_basics.html#bi-directional-associations]. # # The automatic guessing of the inverse association uses a heuristic based # on the name of the class, so it may not work for all associations, # especially the ones with non-standard names. # # You can turn off the automatic detection of inverse associations by setting # the :inverse_of option to false like so: # # class Tagging < ActiveRecord::Base # belongs_to :tag, inverse_of: false # end # # == Nested \Associations # # You can actually specify *any* association with the :through option, including an # association which has a :through option itself. For example: # # class Author < ActiveRecord::Base # has_many :posts # has_many :comments, through: :posts # has_many :commenters, through: :comments # end # # class Post < ActiveRecord::Base # has_many :comments # end # # class Comment < ActiveRecord::Base # belongs_to :commenter # end # # @author = Author.first # @author.commenters # => People who commented on posts written by the author # # An equivalent way of setting up this association this would be: # # class Author < ActiveRecord::Base # has_many :posts # has_many :commenters, through: :posts # end # # class Post < ActiveRecord::Base # has_many :comments # has_many :commenters, through: :comments # end # # class Comment < ActiveRecord::Base # belongs_to :commenter # end # # When using a nested association, you will not be able to modify the association because there # is not enough information to know what modification to make. For example, if you tried to # add a Commenter in the example above, there would be no way to tell how to set up the # intermediate Post and Comment objects. # # == Polymorphic \Associations # # Polymorphic associations on models are not restricted on what types of models they # can be associated with. Rather, they specify an interface that a #has_many association # must adhere to. # # class Asset < ActiveRecord::Base # belongs_to :attachable, polymorphic: true # end # # class Post < ActiveRecord::Base # has_many :assets, as: :attachable # The :as option specifies the polymorphic interface to use. # end # # @asset.attachable = @post # # This works by using a type column in addition to a foreign key to specify the associated # record. In the Asset example, you'd need an +attachable_id+ integer column and an # +attachable_type+ string column. # # Using polymorphic associations in combination with single table inheritance (STI) is # a little tricky. In order for the associations to work as expected, ensure that you # store the base model for the STI models in the type column of the polymorphic # association. To continue with the asset example above, suppose there are guest posts # and member posts that use the posts table for STI. In this case, there must be a +type+ # column in the posts table. # # Note: The attachable_type= method is being called when assigning an +attachable+. # The +class_name+ of the +attachable+ is passed as a String. # # class Asset < ActiveRecord::Base # belongs_to :attachable, polymorphic: true # # def attachable_type=(class_name) # super(class_name.constantize.base_class.to_s) # end # end # # class Post < ActiveRecord::Base # # because we store "Post" in attachable_type now dependent: :destroy will work # has_many :assets, as: :attachable, dependent: :destroy # end # # class GuestPost < Post # end # # class MemberPost < Post # end # # == Caching # # All of the methods are built on a simple caching principle that will keep the result # of the last query around unless specifically instructed not to. The cache is even # shared across methods to make it even cheaper to use the macro-added methods without # worrying too much about performance at the first go. # # project.milestones # fetches milestones from the database # project.milestones.size # uses the milestone cache # project.milestones.empty? # uses the milestone cache # project.milestones.reload.size # fetches milestones from the database # project.milestones # uses the milestone cache # # == Eager loading of associations # # Eager loading is a way to find objects of a certain class and a number of named associations. # It is one of the easiest ways to prevent the dreaded N+1 problem in which fetching 100 # posts that each need to display their author triggers 101 database queries. Through the # use of eager loading, the number of queries will be reduced from 101 to 2. # # class Post < ActiveRecord::Base # belongs_to :author # has_many :comments # end # # Consider the following loop using the class above: # # Post.all.each do |post| # puts "Post: " + post.title # puts "Written by: " + post.author.name # puts "Last comment on: " + post.comments.first.created_on # end # # To iterate over these one hundred posts, we'll generate 201 database queries. Let's # first just optimize it for retrieving the author: # # Post.includes(:author).each do |post| # # This references the name of the #belongs_to association that also used the :author # symbol. After loading the posts, +find+ will collect the +author_id+ from each one and load # all of the referenced authors with one query. Doing so will cut down the number of queries # from 201 to 102. # # We can improve upon the situation further by referencing both associations in the finder with: # # Post.includes(:author, :comments).each do |post| # # This will load all comments with a single query. This reduces the total number of queries # to 3. In general, the number of queries will be 1 plus the number of associations # named (except if some of the associations are polymorphic #belongs_to - see below). # # To include a deep hierarchy of associations, use a hash: # # Post.includes(:author, { comments: { author: :gravatar } }).each do |post| # # The above code will load all the comments and all of their associated # authors and gravatars. You can mix and match any combination of symbols, # arrays, and hashes to retrieve the associations you want to load. # # All of this power shouldn't fool you into thinking that you can pull out huge amounts # of data with no performance penalty just because you've reduced the number of queries. # The database still needs to send all the data to Active Record and it still needs to # be processed. So it's no catch-all for performance problems, but it's a great way to # cut down on the number of queries in a situation as the one described above. # # Since only one table is loaded at a time, conditions or orders cannot reference tables # other than the main one. If this is the case, Active Record falls back to the previously # used LEFT OUTER JOIN based strategy. For example: # # Post.includes([:author, :comments]).where(['comments.approved = ?', true]) # # This will result in a single SQL query with joins along the lines of: # LEFT OUTER JOIN comments ON comments.post_id = posts.id and # LEFT OUTER JOIN authors ON authors.id = posts.author_id. Note that using conditions # like this can have unintended consequences. # In the above example, posts with no approved comments are not returned at all because # the conditions apply to the SQL statement as a whole and not just to the association. # # You must disambiguate column references for this fallback to happen, for example # order: "author.name DESC" will work but order: "name DESC" will not. # # If you want to load all posts (including posts with no approved comments), then write # your own LEFT OUTER JOIN query using ON: # # Post.joins("LEFT OUTER JOIN comments ON comments.post_id = posts.id AND comments.approved = '1'") # # In this case, it is usually more natural to include an association which has conditions defined on it: # # class Post < ActiveRecord::Base # has_many :approved_comments, -> { where(approved: true) }, class_name: 'Comment' # end # # Post.includes(:approved_comments) # # This will load posts and eager load the +approved_comments+ association, which contains # only those comments that have been approved. # # If you eager load an association with a specified :limit option, it will be ignored, # returning all the associated objects: # # class Picture < ActiveRecord::Base # has_many :most_recent_comments, -> { order('id DESC').limit(10) }, class_name: 'Comment' # end # # Picture.includes(:most_recent_comments).first.most_recent_comments # => returns all associated comments. # # Eager loading is supported with polymorphic associations. # # class Address < ActiveRecord::Base # belongs_to :addressable, polymorphic: true # end # # A call that tries to eager load the addressable model # # Address.includes(:addressable) # # This will execute one query to load the addresses and load the addressables with one # query per addressable type. # For example, if all the addressables are either of class Person or Company, then a total # of 3 queries will be executed. The list of addressable types to load is determined on # the back of the addresses loaded. This is not supported if Active Record has to fall back # to the previous implementation of eager loading and will raise ActiveRecord::EagerLoadPolymorphicError. # The reason is that the parent model's type is a column value so its corresponding table # name cannot be put in the +FROM+/+JOIN+ clauses of that query. # # == Table Aliasing # # Active Record uses table aliasing in the case that a table is referenced multiple times # in a join. If a table is referenced only once, the standard table name is used. The # second time, the table is aliased as #{reflection_name}_#{parent_table_name}. # Indexes are appended for any more successive uses of the table name. # # Post.joins(:comments) # # SELECT ... FROM posts INNER JOIN comments ON ... # Post.joins(:special_comments) # STI # # SELECT ... FROM posts INNER JOIN comments ON ... AND comments.type = 'SpecialComment' # Post.joins(:comments, :special_comments) # special_comments is the reflection name, posts is the parent table name # # SELECT ... FROM posts INNER JOIN comments ON ... INNER JOIN comments special_comments_posts # # Acts as tree example: # # TreeMixin.joins(:children) # # SELECT ... FROM mixins INNER JOIN mixins childrens_mixins ... # TreeMixin.joins(children: :parent) # # SELECT ... FROM mixins INNER JOIN mixins childrens_mixins ... # # INNER JOIN parents_mixins ... # TreeMixin.joins(children: {parent: :children}) # # SELECT ... FROM mixins INNER JOIN mixins childrens_mixins ... # # INNER JOIN parents_mixins ... # # INNER JOIN mixins childrens_mixins_2 # # Has and Belongs to Many join tables use the same idea, but add a _join suffix: # # Post.joins(:categories) # # SELECT ... FROM posts INNER JOIN categories_posts ... INNER JOIN categories ... # Post.joins(categories: :posts) # # SELECT ... FROM posts INNER JOIN categories_posts ... INNER JOIN categories ... # # INNER JOIN categories_posts posts_categories_join INNER JOIN posts posts_categories # Post.joins(categories: {posts: :categories}) # # SELECT ... FROM posts INNER JOIN categories_posts ... INNER JOIN categories ... # # INNER JOIN categories_posts posts_categories_join INNER JOIN posts posts_categories # # INNER JOIN categories_posts categories_posts_join INNER JOIN categories categories_posts_2 # # If you wish to specify your own custom joins using ActiveRecord::QueryMethods#joins method, those table # names will take precedence over the eager associations: # # Post.joins(:comments).joins("inner join comments ...") # # SELECT ... FROM posts INNER JOIN comments_posts ON ... INNER JOIN comments ... # Post.joins(:comments, :special_comments).joins("inner join comments ...") # # SELECT ... FROM posts INNER JOIN comments comments_posts ON ... # # INNER JOIN comments special_comments_posts ... # # INNER JOIN comments ... # # Table aliases are automatically truncated according to the maximum length of table identifiers # according to the specific database. # # == Modules # # By default, associations will look for objects within the current module scope. Consider: # # module MyApplication # module Business # class Firm < ActiveRecord::Base # has_many :clients # end # # class Client < ActiveRecord::Base; end # end # end # # When Firm#clients is called, it will in turn call # MyApplication::Business::Client.find_all_by_firm_id(firm.id). # If you want to associate with a class in another module scope, this can be done by # specifying the complete class name. # # module MyApplication # module Business # class Firm < ActiveRecord::Base; end # end # # module Billing # class Account < ActiveRecord::Base # belongs_to :firm, class_name: "MyApplication::Business::Firm" # end # end # end # # == Bi-directional associations # # When you specify an association, there is usually an association on the associated model # that specifies the same relationship in reverse. For example, with the following models: # # class Dungeon < ActiveRecord::Base # has_many :traps # has_one :evil_wizard # end # # class Trap < ActiveRecord::Base # belongs_to :dungeon # end # # class EvilWizard < ActiveRecord::Base # belongs_to :dungeon # end # # The +traps+ association on +Dungeon+ and the +dungeon+ association on +Trap+ are # the inverse of each other, and the inverse of the +dungeon+ association on +EvilWizard+ # is the +evil_wizard+ association on +Dungeon+ (and vice-versa). By default, # Active Record can guess the inverse of the association based on the name # of the class. The result is the following: # # d = Dungeon.first # t = d.traps.first # d.object_id == t.dungeon.object_id # => true # # The +Dungeon+ instances +d+ and t.dungeon in the above example refer to # the same in-memory instance since the association matches the name of the class. # The result would be the same if we added +:inverse_of+ to our model definitions: # # class Dungeon < ActiveRecord::Base # has_many :traps, inverse_of: :dungeon # has_one :evil_wizard, inverse_of: :dungeon # end # # class Trap < ActiveRecord::Base # belongs_to :dungeon, inverse_of: :traps # end # # class EvilWizard < ActiveRecord::Base # belongs_to :dungeon, inverse_of: :evil_wizard # end # # For more information, see the documentation for the +:inverse_of+ option and the # {Active Record Associations guide}[https://guides.rubyonrails.org/association_basics.html#bi-directional-associations]. # # == Deleting from associations # # === Dependent associations # # #has_many, #has_one, and #belongs_to associations support the :dependent option. # This allows you to specify that associated records should be deleted when the owner is # deleted. # # For example: # # class Author # has_many :posts, dependent: :destroy # end # Author.find(1).destroy # => Will destroy all of the author's posts, too # # The :dependent option can have different values which specify how the deletion # is done. For more information, see the documentation for this option on the different # specific association types. When no option is given, the behavior is to do nothing # with the associated records when destroying a record. # # Note that :dependent is implemented using \Rails' callback # system, which works by processing callbacks in order. Therefore, other # callbacks declared either before or after the :dependent option # can affect what it does. # # Note that :dependent option is ignored for #has_one :through associations. # # === Delete or destroy? # # #has_many and #has_and_belongs_to_many associations have the methods destroy, # delete, destroy_all and delete_all. # # For #has_and_belongs_to_many, delete and destroy are the same: they # cause the records in the join table to be removed. # # For #has_many, destroy and destroy_all will always call the destroy method of the # record(s) being removed so that callbacks are run. However delete and delete_all will either # do the deletion according to the strategy specified by the :dependent option, or # if no :dependent option is given, then it will follow the default strategy. # The default strategy is to do nothing (leave the foreign keys with the parent ids set), except for # #has_many :through, where the default strategy is delete_all (delete # the join records, without running their callbacks). # # There is also a clear method which is the same as delete_all, except that # it returns the association rather than the records which have been deleted. # # === What gets deleted? # # There is a potential pitfall here: #has_and_belongs_to_many and #has_many :through # associations have records in join tables, as well as the associated records. So when we # call one of these deletion methods, what exactly should be deleted? # # The answer is that it is assumed that deletion on an association is about removing the # link between the owner and the associated object(s), rather than necessarily the # associated objects themselves. So with #has_and_belongs_to_many and #has_many # :through, the join records will be deleted, but the associated records won't. # # This makes sense if you think about it: if you were to call post.tags.delete(Tag.find_by(name: 'food')) # you would want the 'food' tag to be unlinked from the post, rather than for the tag itself # to be removed from the database. # # However, there are examples where this strategy doesn't make sense. For example, suppose # a person has many projects, and each project has many tasks. If we deleted one of a person's # tasks, we would probably not want the project to be deleted. In this scenario, the delete method # won't actually work: it can only be used if the association on the join model is a # #belongs_to. In other situations you are expected to perform operations directly on # either the associated records or the :through association. # # With a regular #has_many there is no distinction between the "associated records" # and the "link", so there is only one choice for what gets deleted. # # With #has_and_belongs_to_many and #has_many :through, if you want to delete the # associated records themselves, you can always do something along the lines of # person.tasks.each(&:destroy). # # == Type safety with ActiveRecord::AssociationTypeMismatch # # If you attempt to assign an object to an association that doesn't match the inferred # or specified :class_name, you'll get an ActiveRecord::AssociationTypeMismatch. # # == Options # # All of the association macros can be specialized through options. This makes cases # more complex than the simple and guessable ones possible. module ClassMethods # Specifies a one-to-many association. The following methods for retrieval and query of # collections of associated objects will be added: # # +collection+ is a placeholder for the symbol passed as the +name+ argument, so # has_many :clients would add among others clients.empty?. # # [collection] # Returns a Relation of all the associated objects. # An empty Relation is returned if none are found. # [collection<<(object, ...)] # Adds one or more objects to the collection by setting their foreign keys to the collection's primary key. # Note that this operation instantly fires update SQL without waiting for the save or update call on the # parent object, unless the parent object is a new record. # This will also run validations and callbacks of associated object(s). # [collection.delete(object, ...)] # Removes one or more objects from the collection by setting their foreign keys to +NULL+. # Objects will be in addition destroyed if they're associated with dependent: :destroy, # and deleted if they're associated with dependent: :delete_all. # # If the :through option is used, then the join records are deleted (rather than # nullified) by default, but you can specify dependent: :destroy or # dependent: :nullify to override this. # [collection.destroy(object, ...)] # Removes one or more objects from the collection by running destroy on # each record, regardless of any dependent option, ensuring callbacks are run. # # If the :through option is used, then the join records are destroyed # instead, not the objects themselves. # [collection=objects] # Replaces the collections content by deleting and adding objects as appropriate. If the :through # option is true callbacks in the join models are triggered except destroy callbacks, since deletion is # direct by default. You can specify dependent: :destroy or # dependent: :nullify to override this. # [collection_singular_ids] # Returns an array of the associated objects' ids # [collection_singular_ids=ids] # Replace the collection with the objects identified by the primary keys in +ids+. This # method loads the models and calls collection=. See above. # [collection.clear] # Removes every object from the collection. This destroys the associated objects if they # are associated with dependent: :destroy, deletes them directly from the # database if dependent: :delete_all, otherwise sets their foreign keys to +NULL+. # If the :through option is true no destroy callbacks are invoked on the join models. # Join models are directly deleted. # [collection.empty?] # Returns +true+ if there are no associated objects. # [collection.size] # Returns the number of associated objects. # [collection.find(...)] # Finds an associated object according to the same rules as ActiveRecord::FinderMethods#find. # [collection.exists?(...)] # Checks whether an associated object with the given conditions exists. # Uses the same rules as ActiveRecord::FinderMethods#exists?. # [collection.build(attributes = {}, ...)] # Returns one or more new objects of the collection type that have been instantiated # with +attributes+ and linked to this object through a foreign key, but have not yet # been saved. # [collection.create(attributes = {})] # Returns a new object of the collection type that has been instantiated # with +attributes+, linked to this object through a foreign key, and that has already # been saved (if it passed the validation). *Note*: This only works if the base model # already exists in the DB, not if it is a new (unsaved) record! # [collection.create!(attributes = {})] # Does the same as collection.create, but raises ActiveRecord::RecordInvalid # if the record is invalid. # [collection.reload] # Returns a Relation of all of the associated objects, forcing a database read. # An empty Relation is returned if none are found. # # ==== Example # # class Firm < ActiveRecord::Base # has_many :clients # end # # Declaring has_many :clients adds the following methods (and more): # # firm = Firm.find(2) # client = Client.find(6) # # firm.clients # similar to Client.where(firm_id: 2) # firm.clients << client # firm.clients.delete(client) # firm.clients.destroy(client) # firm.clients = [client] # firm.client_ids # firm.client_ids = [6] # firm.clients.clear # firm.clients.empty? # similar to firm.clients.size == 0 # firm.clients.size # similar to Client.count "firm_id = 2" # firm.clients.find # similar to Client.where(firm_id: 2).find(6) # firm.clients.exists?(name: 'ACME') # similar to Client.exists?(name: 'ACME', firm_id: 2) # firm.clients.build # similar to Client.new(firm_id: 2) # firm.clients.create # similar to Client.create(firm_id: 2) # firm.clients.create! # similar to Client.create!(firm_id: 2) # firm.clients.reload # # The declaration can also include an +options+ hash to specialize the behavior of the association. # # ==== Scopes # # You can pass a second argument +scope+ as a callable (i.e. proc or # lambda) to retrieve a specific set of records or customize the generated # query when you access the associated collection. # # Scope examples: # has_many :comments, -> { where(author_id: 1) } # has_many :employees, -> { joins(:address) } # has_many :posts, ->(blog) { where("max_post_length > ?", blog.max_post_length) } # # ==== Extensions # # The +extension+ argument allows you to pass a block into a has_many # association. This is useful for adding new finders, creators, and other # factory-type methods to be used as part of the association. # # Extension examples: # has_many :employees do # def find_or_create_by_name(name) # first_name, last_name = name.split(" ", 2) # find_or_create_by(first_name: first_name, last_name: last_name) # end # end # # ==== Options # [+:class_name+] # Specify the class name of the association. Use it only if that name can't be inferred # from the association name. So has_many :products will by default be linked # to the +Product+ class, but if the real class name is +SpecialProduct+, you'll have to # specify it with this option. # [+:foreign_key+] # Specify the foreign key used for the association. By default this is guessed to be the name # of this class in lower-case and "_id" suffixed. So a Person class that makes a #has_many # association will use "person_id" as the default :foreign_key. # # Setting the :foreign_key option prevents automatic detection of the association's # inverse, so it is generally a good idea to set the :inverse_of option as well. # [+:foreign_type+] # Specify the column used to store the associated object's type, if this is a polymorphic # association. By default this is guessed to be the name of the polymorphic association # specified on "as" option with a "_type" suffix. So a class that defines a # has_many :tags, as: :taggable association will use "taggable_type" as the # default :foreign_type. # [+:primary_key+] # Specify the name of the column to use as the primary key for the association. By default this is +id+. # [+:dependent+] # Controls what happens to the associated objects when # their owner is destroyed. Note that these are implemented as # callbacks, and \Rails executes callbacks in order. Therefore, other # similar callbacks may affect the :dependent behavior, and the # :dependent behavior may affect other callbacks. # # * nil do nothing (default). # * :destroy causes all the associated objects to also be destroyed. # * :destroy_async destroys all the associated objects in a background job. WARNING: Do not use # this option if the association is backed by foreign key constraints in your database. The foreign key # constraint actions will occur inside the same transaction that deletes its owner. # * :delete_all causes all the associated objects to be deleted directly from the database (so callbacks will not be executed). # * :nullify causes the foreign keys to be set to +NULL+. Polymorphic type will also be nullified # on polymorphic associations. Callbacks are not executed. # * :restrict_with_exception causes an ActiveRecord::DeleteRestrictionError exception to be raised if there are any associated records. # * :restrict_with_error causes an error to be added to the owner if there are any associated objects. # # If using with the :through option, the association on the join model must be # a #belongs_to, and the records which get deleted are the join records, rather than # the associated records. # # If using dependent: :destroy on a scoped association, only the scoped objects are destroyed. # For example, if a Post model defines # has_many :comments, -> { where published: true }, dependent: :destroy and destroy is # called on a post, only published comments are destroyed. This means that any unpublished comments in the # database would still contain a foreign key pointing to the now deleted post. # [+:counter_cache+] # This option can be used to configure a custom named :counter_cache. You only need this option, # when you customized the name of your :counter_cache on the #belongs_to association. # [+:as+] # Specifies a polymorphic interface (See #belongs_to). # [+:through+] # Specifies an association through which to perform the query. This can be any other type # of association, including other :through associations. Options for :class_name, # :primary_key and :foreign_key are ignored, as the association uses the # source reflection. # # If the association on the join model is a #belongs_to, the collection can be modified # and the records on the :through model will be automatically created and removed # as appropriate. Otherwise, the collection is read-only, so you should manipulate the # :through association directly. # # If you are going to modify the association (rather than just read from it), then it is # a good idea to set the :inverse_of option on the source association on the # join model. This allows associated records to be built which will automatically create # the appropriate join model records when they are saved. See # {Association Join Models}[rdoc-ref:Associations::ClassMethods@Association+Join+Models] # and {Setting Inverses}[rdoc-ref:Associations::ClassMethods@Setting+Inverses] for # more detail. # # [+:disable_joins+] # Specifies whether joins should be skipped for an association. If set to true, two or more queries # will be generated. Note that in some cases, if order or limit is applied, it will be done in-memory # due to database limitations. This option is only applicable on has_many :through associations as # +has_many+ alone do not perform a join. # [+:source+] # Specifies the source association name used by #has_many :through queries. # Only use it if the name cannot be inferred from the association. # has_many :subscribers, through: :subscriptions will look for either :subscribers or # :subscriber on Subscription, unless a :source is given. # [+:source_type+] # Specifies type of the source association used by #has_many :through queries where the source # association is a polymorphic #belongs_to. # [+:validate+] # When set to +true+, validates new objects added to association when saving the parent object. +true+ by default. # If you want to ensure associated objects are revalidated on every update, use +validates_associated+. # [+:autosave+] # If true, always save the associated objects or destroy them if marked for destruction, # when saving the parent object. If false, never save or destroy the associated objects. # By default, only save associated objects that are new records. This option is implemented as a # +before_save+ callback. Because callbacks are run in the order they are defined, associated objects # may need to be explicitly saved in any user-defined +before_save+ callbacks. # # Note that NestedAttributes::ClassMethods#accepts_nested_attributes_for sets # :autosave to true. # [+:inverse_of+] # Specifies the name of the #belongs_to association on the associated object # that is the inverse of this #has_many association. # See {Bi-directional associations}[rdoc-ref:Associations::ClassMethods@Bi-directional+associations] # for more detail. # [+:extend+] # Specifies a module or array of modules that will be extended into the association object returned. # Useful for defining methods on associations, especially when they should be shared between multiple # association objects. # [+:strict_loading+] # When set to +true+, enforces strict loading every time the associated record is loaded through this # association. # [+:ensuring_owner_was+] # Specifies an instance method to be called on the owner. The method must return true in order for the # associated records to be deleted in a background job. # [+:query_constraints+] # Serves as a composite foreign key. Defines the list of columns to be used to query the associated object. # This is an optional option. By default Rails will attempt to derive the value automatically. # When the value is set the Array size must match associated model's primary key or +query_constraints+ size. # [+:index_errors+] # Allows differentiation of multiple validation errors from the association records, by including # an index in the error attribute name, e.g. +roles[2].level+. # When set to +true+, the index is based on association order, i.e. database order, with yet to be # persisted new records placed at the end. # When set to +:nested_attributes_order+, the index is based on the record order received by # nested attributes setter, when accepts_nested_attributes_for is used. # [:before_add] # Defines an {association callback}[rdoc-ref:Associations::ClassMethods@Association+callbacks] that gets triggered before an object is added to the association collection. # [:after_add] # Defines an {association callback}[rdoc-ref:Associations::ClassMethods@Association+callbacks] that gets triggered after an object is added to the association collection. # [:before_remove] # Defines an {association callback}[rdoc-ref:Associations::ClassMethods@Association+callbacks] that gets triggered before an object is removed from the association collection. # [:after_remove] # Defines an {association callback}[rdoc-ref:Associations::ClassMethods@Association+callbacks] that gets triggered after an object is removed from the association collection. # # Option examples: # has_many :comments, -> { order("posted_on") } # has_many :comments, -> { includes(:author) } # has_many :people, -> { where(deleted: false).order("name") }, class_name: "Person" # has_many :tracks, -> { order("position") }, dependent: :destroy # has_many :comments, dependent: :nullify # has_many :tags, as: :taggable # has_many :reports, -> { readonly } # has_many :subscribers, through: :subscriptions, source: :user # has_many :subscribers, through: :subscriptions, disable_joins: true # has_many :comments, strict_loading: true # has_many :comments, query_constraints: [:blog_id, :post_id] # has_many :comments, index_errors: :nested_attributes_order def has_many(name, scope = nil, **options, &extension) reflection = Builder::HasMany.build(self, name, scope, options, &extension) Reflection.add_reflection self, name, reflection end # Specifies a one-to-one association with another class. This method # should only be used if the other class contains the foreign key. If # the current class contains the foreign key, then you should use # #belongs_to instead. See {Is it a belongs_to or has_one # association?}[rdoc-ref:Associations::ClassMethods@Is+it+a+-23belongs_to+or+-23has_one+association-3F] # for more detail on when to use #has_one and when to use #belongs_to. # # The following methods for retrieval and query of a single associated object will be added: # # +association+ is a placeholder for the symbol passed as the +name+ argument, so # has_one :manager would add among others manager.nil?. # # [association] # Returns the associated object. +nil+ is returned if none is found. # [association=(associate)] # Assigns the associate object, extracts the primary key, sets it as the foreign key, # and saves the associate object. To avoid database inconsistencies, permanently deletes an existing # associated object when assigning a new one, even if the new one isn't saved to database. # [build_association(attributes = {})] # Returns a new object of the associated type that has been instantiated # with +attributes+ and linked to this object through a foreign key, but has not # yet been saved. # [create_association(attributes = {})] # Returns a new object of the associated type that has been instantiated # with +attributes+, linked to this object through a foreign key, and that # has already been saved (if it passed the validation). # [create_association!(attributes = {})] # Does the same as create_association, but raises ActiveRecord::RecordInvalid # if the record is invalid. # [reload_association] # Returns the associated object, forcing a database read. # [reset_association] # Unloads the associated object. The next access will query it from the database. # # ==== Example # # class Account < ActiveRecord::Base # has_one :beneficiary # end # # Declaring has_one :beneficiary adds the following methods (and more): # # account = Account.find(5) # beneficiary = Beneficiary.find(8) # # account.beneficiary # similar to Beneficiary.find_by(account_id: 5) # account.beneficiary = beneficiary # similar to beneficiary.update(account_id: 5) # account.build_beneficiary # similar to Beneficiary.new(account_id: 5) # account.create_beneficiary # similar to Beneficiary.create(account_id: 5) # account.create_beneficiary! # similar to Beneficiary.create!(account_id: 5) # account.reload_beneficiary # account.reset_beneficiary # # ==== Scopes # # You can pass a second argument +scope+ as a callable (i.e. proc or # lambda) to retrieve a specific record or customize the generated query # when you access the associated object. # # Scope examples: # has_one :author, -> { where(comment_id: 1) } # has_one :employer, -> { joins(:company) } # has_one :latest_post, ->(blog) { where("created_at > ?", blog.enabled_at) } # # ==== Options # # The declaration can also include an +options+ hash to specialize the behavior of the association. # # Options are: # [+:class_name+] # Specify the class name of the association. Use it only if that name can't be inferred # from the association name. So has_one :manager will by default be linked to the Manager class, but # if the real class name is Person, you'll have to specify it with this option. # [+:dependent+] # Controls what happens to the associated object when # its owner is destroyed: # # * nil do nothing (default). # * :destroy causes the associated object to also be destroyed # * :destroy_async causes the associated object to be destroyed in a background job. WARNING: Do not use # this option if the association is backed by foreign key constraints in your database. The foreign key # constraint actions will occur inside the same transaction that deletes its owner. # * :delete causes the associated object to be deleted directly from the database (so callbacks will not execute) # * :nullify causes the foreign key to be set to +NULL+. Polymorphic type column is also nullified # on polymorphic associations. Callbacks are not executed. # * :restrict_with_exception causes an ActiveRecord::DeleteRestrictionError exception to be raised if there is an associated record # * :restrict_with_error causes an error to be added to the owner if there is an associated object # # Note that :dependent option is ignored when using :through option. # [+:foreign_key+] # Specify the foreign key used for the association. By default this is guessed to be the name # of this class in lower-case and "_id" suffixed. So a Person class that makes a #has_one association # will use "person_id" as the default :foreign_key. # # Setting the :foreign_key option prevents automatic detection of the association's # inverse, so it is generally a good idea to set the :inverse_of option as well. # [+:foreign_type+] # Specify the column used to store the associated object's type, if this is a polymorphic # association. By default this is guessed to be the name of the polymorphic association # specified on "as" option with a "_type" suffix. So a class that defines a # has_one :tag, as: :taggable association will use "taggable_type" as the # default :foreign_type. # [+:primary_key+] # Specify the method that returns the primary key used for the association. By default this is +id+. # [+:as+] # Specifies a polymorphic interface (See #belongs_to). # [+:through+] # Specifies a Join Model through which to perform the query. Options for :class_name, # :primary_key, and :foreign_key are ignored, as the association uses the # source reflection. You can only use a :through query through a #has_one # or #belongs_to association on the join model. # # If the association on the join model is a #belongs_to, the collection can be modified # and the records on the :through model will be automatically created and removed # as appropriate. Otherwise, the collection is read-only, so you should manipulate the # :through association directly. # # If you are going to modify the association (rather than just read from it), then it is # a good idea to set the :inverse_of option on the source association on the # join model. This allows associated records to be built which will automatically create # the appropriate join model records when they are saved. See # {Association Join Models}[rdoc-ref:Associations::ClassMethods@Association+Join+Models] # and {Setting Inverses}[rdoc-ref:Associations::ClassMethods@Setting+Inverses] for # more detail. # [+:disable_joins+] # Specifies whether joins should be skipped for an association. If set to true, two or more queries # will be generated. Note that in some cases, if order or limit is applied, it will be done in-memory # due to database limitations. This option is only applicable on has_one :through associations as # +has_one+ alone does not perform a join. # [+:source+] # Specifies the source association name used by #has_one :through queries. # Only use it if the name cannot be inferred from the association. # has_one :favorite, through: :favorites will look for a # :favorite on Favorite, unless a :source is given. # [+:source_type+] # Specifies type of the source association used by #has_one :through queries where the source # association is a polymorphic #belongs_to. # [+:validate+] # When set to +true+, validates new objects added to association when saving the parent object. +false+ by default. # If you want to ensure associated objects are revalidated on every update, use +validates_associated+. # [+:autosave+] # If +true+, always saves the associated object or destroys it if marked for destruction, # when saving the parent object. # If +false+, never save or destroy the associated object. # # By default, only saves the associated object if it's a new record. Setting this option # to +true+ also enables validations on the associated object unless explicitly disabled # with validate: false. This is because saving an object with invalid associated # objects would fail, so any associated objects will go through validation checks. # # Note that NestedAttributes::ClassMethods#accepts_nested_attributes_for sets # :autosave to true. # [+:touch+] # If true, the associated object will be touched (the +updated_at+ / +updated_on+ attributes set to current time) # when this record is either saved or destroyed. If you specify a symbol, that attribute # will be updated with the current time in addition to the +updated_at+ / +updated_on+ attribute. # Please note that no validation will be performed when touching, and only the +after_touch+, # +after_commit+, and +after_rollback+ callbacks will be executed. # [+:inverse_of+] # Specifies the name of the #belongs_to association on the associated object # that is the inverse of this #has_one association. # See {Bi-directional associations}[rdoc-ref:Associations::ClassMethods@Bi-directional+associations] # for more detail. # [+:required+] # When set to +true+, the association will also have its presence validated. # This will validate the association itself, not the id. You can use # +:inverse_of+ to avoid an extra query during validation. # [+:strict_loading+] # Enforces strict loading every time the associated record is loaded through this association. # [+:ensuring_owner_was+] # Specifies an instance method to be called on the owner. The method must return true in order for the # associated records to be deleted in a background job. # [+:query_constraints+] # Serves as a composite foreign key. Defines the list of columns to be used to query the associated object. # This is an optional option. By default Rails will attempt to derive the value automatically. # When the value is set the Array size must match associated model's primary key or +query_constraints+ size. # # Option examples: # has_one :credit_card, dependent: :destroy # destroys the associated credit card # has_one :credit_card, dependent: :nullify # updates the associated records foreign # # key value to NULL rather than destroying it # has_one :last_comment, -> { order('posted_on') }, class_name: "Comment" # has_one :project_manager, -> { where(role: 'project_manager') }, class_name: "Person" # has_one :attachment, as: :attachable # has_one :boss, -> { readonly } # has_one :club, through: :membership # has_one :club, through: :membership, disable_joins: true # has_one :primary_address, -> { where(primary: true) }, through: :addressables, source: :addressable # has_one :credit_card, required: true # has_one :credit_card, strict_loading: true # has_one :employment_record_book, query_constraints: [:organization_id, :employee_id] def has_one(name, scope = nil, **options) reflection = Builder::HasOne.build(self, name, scope, options) Reflection.add_reflection self, name, reflection end # Specifies a one-to-one association with another class. This method # should only be used if this class contains the foreign key. If the # other class contains the foreign key, then you should use #has_one # instead. See {Is it a belongs_to or has_one # association?}[rdoc-ref:Associations::ClassMethods@Is+it+a+-23belongs_to+or+-23has_one+association-3F] # for more detail on when to use #has_one and when to use #belongs_to. # # Methods will be added for retrieval and query for a single associated object, for which # this object holds an id: # # +association+ is a placeholder for the symbol passed as the +name+ argument, so # belongs_to :author would add among others author.nil?. # # [association] # Returns the associated object. +nil+ is returned if none is found. # [association=(associate)] # Assigns the associate object, extracts the primary key, and sets it as the foreign key. # No modification or deletion of existing records takes place. # [build_association(attributes = {})] # Returns a new object of the associated type that has been instantiated # with +attributes+ and linked to this object through a foreign key, but has not yet been saved. # [create_association(attributes = {})] # Returns a new object of the associated type that has been instantiated # with +attributes+, linked to this object through a foreign key, and that # has already been saved (if it passed the validation). # [create_association!(attributes = {})] # Does the same as create_association, but raises ActiveRecord::RecordInvalid # if the record is invalid. # [reload_association] # Returns the associated object, forcing a database read. # [reset_association] # Unloads the associated object. The next access will query it from the database. # [association_changed?] # Returns true if a new associate object has been assigned and the next save will update the foreign key. # [association_previously_changed?] # Returns true if the previous save updated the association to reference a new associate object. # # ==== Example # # class Post < ActiveRecord::Base # belongs_to :author # end # # Declaring belongs_to :author adds the following methods (and more): # # post = Post.find(7) # author = Author.find(19) # # post.author # similar to Author.find(post.author_id) # post.author = author # similar to post.author_id = author.id # post.build_author # similar to post.author = Author.new # post.create_author # similar to post.author = Author.new; post.author.save; post.author # post.create_author! # similar to post.author = Author.new; post.author.save!; post.author # post.reload_author # post.reset_author # post.author_changed? # post.author_previously_changed? # # ==== Scopes # # You can pass a second argument +scope+ as a callable (i.e. proc or # lambda) to retrieve a specific record or customize the generated query # when you access the associated object. # # Scope examples: # belongs_to :firm, -> { where(id: 2) } # belongs_to :user, -> { joins(:friends) } # belongs_to :level, ->(game) { where("game_level > ?", game.current_level) } # # ==== Options # # The declaration can also include an +options+ hash to specialize the behavior of the association. # # [+:class_name+] # Specify the class name of the association. Use it only if that name can't be inferred # from the association name. So belongs_to :author will by default be linked to the Author class, but # if the real class name is Person, you'll have to specify it with this option. # [+:foreign_key+] # Specify the foreign key used for the association. By default this is guessed to be the name # of the association with an "_id" suffix. So a class that defines a belongs_to :person # association will use "person_id" as the default :foreign_key. Similarly, # belongs_to :favorite_person, class_name: "Person" will use a foreign key # of "favorite_person_id". # # Setting the :foreign_key option prevents automatic detection of the association's # inverse, so it is generally a good idea to set the :inverse_of option as well. # [+:foreign_type+] # Specify the column used to store the associated object's type, if this is a polymorphic # association. By default this is guessed to be the name of the association with a "_type" # suffix. So a class that defines a belongs_to :taggable, polymorphic: true # association will use "taggable_type" as the default :foreign_type. # [+:primary_key+] # Specify the method that returns the primary key of associated object used for the association. # By default this is +id+. # [+:dependent+] # If set to :destroy, the associated object is destroyed when this object is. If set to # :delete, the associated object is deleted *without* calling its destroy method. If set to # :destroy_async, the associated object is scheduled to be destroyed in a background job. # This option should not be specified when #belongs_to is used in conjunction with # a #has_many relationship on another class because of the potential to leave # orphaned records behind. # [+:counter_cache+] # Caches the number of belonging objects on the associate class through the use of CounterCache::ClassMethods#increment_counter # and CounterCache::ClassMethods#decrement_counter. The counter cache is incremented when an object of this # class is created and decremented when it's destroyed. This requires that a column # named #{table_name}_count (such as +comments_count+ for a belonging Comment class) # is used on the associate class (such as a Post class) - that is the migration for # #{table_name}_count is created on the associate class (such that Post.comments_count will # return the count cached). You can also specify a custom counter # cache column by providing a column name instead of a +true+/+false+ value to this # option (e.g., counter_cache: :my_custom_counter.) # # Starting to use counter caches on existing large tables can be troublesome, because the column # values must be backfilled separately of the column addition (to not lock the table for too long) # and before the use of +:counter_cache+ (otherwise methods like +size+/+any?+/etc, which use # counter caches internally, can produce incorrect results). To safely backfill the values while keeping # counter cache columns updated with the child records creation/removal and to avoid the mentioned methods # use the possibly incorrect counter cache column values and always get the results from the database, # use counter_cache: { active: false }. # If you also need to specify a custom column name, use counter_cache: { active: false, column: :my_custom_counter }. # # Note: If you've enabled the counter cache, then you may want to add the counter cache attribute # to the +attr_readonly+ list in the associated classes (e.g. class Post; attr_readonly :comments_count; end). # [+:polymorphic+] # Specify this association is a polymorphic association by passing +true+. # Note: Since polymorphic associations rely on storing class names in the database, make sure to update the class names in the # *_type polymorphic type column of the corresponding rows. # [+:validate+] # When set to +true+, validates new objects added to association when saving the parent object. +false+ by default. # If you want to ensure associated objects are revalidated on every update, use +validates_associated+. # [+:autosave+] # If true, always save the associated object or destroy it if marked for destruction, when # saving the parent object. # If false, never save or destroy the associated object. # By default, only save the associated object if it's a new record. # # Note that NestedAttributes::ClassMethods#accepts_nested_attributes_for # sets :autosave to true. # [+:touch+] # If true, the associated object will be touched (the +updated_at+ / +updated_on+ attributes set to current time) # when this record is either saved or destroyed. If you specify a symbol, that attribute # will be updated with the current time in addition to the +updated_at+ / +updated_on+ attribute. # Please note that no validation will be performed when touching, and only the +after_touch+, # +after_commit+, and +after_rollback+ callbacks will be executed. # [+:inverse_of+] # Specifies the name of the #has_one or #has_many association on the associated # object that is the inverse of this #belongs_to association. # See {Bi-directional associations}[rdoc-ref:Associations::ClassMethods@Bi-directional+associations] # for more detail. # [+:optional+] # When set to +true+, the association will not have its presence validated. # [+:required+] # When set to +true+, the association will also have its presence validated. # This will validate the association itself, not the id. You can use # +:inverse_of+ to avoid an extra query during validation. # NOTE: required is set to true by default and is deprecated. If # you don't want to have association presence validated, use optional: true. # [+:default+] # Provide a callable (i.e. proc or lambda) to specify that the association should # be initialized with a particular record before validation. # Please note that callable won't be executed if the record exists. # [+:strict_loading+] # Enforces strict loading every time the associated record is loaded through this association. # [+:ensuring_owner_was+] # Specifies an instance method to be called on the owner. The method must return true in order for the # associated records to be deleted in a background job. # [+:query_constraints+] # Serves as a composite foreign key. Defines the list of columns to be used to query the associated object. # This is an optional option. By default Rails will attempt to derive the value automatically. # When the value is set the Array size must match associated model's primary key or +query_constraints+ size. # # Option examples: # belongs_to :firm, foreign_key: "client_of" # belongs_to :person, primary_key: "name", foreign_key: "person_name" # belongs_to :author, class_name: "Person", foreign_key: "author_id" # belongs_to :valid_coupon, ->(o) { where "discounts > ?", o.payments_count }, # class_name: "Coupon", foreign_key: "coupon_id" # belongs_to :attachable, polymorphic: true # belongs_to :project, -> { readonly } # belongs_to :post, counter_cache: true # belongs_to :comment, touch: true # belongs_to :company, touch: :employees_last_updated_at # belongs_to :user, optional: true # belongs_to :account, default: -> { company.account } # belongs_to :account, strict_loading: true # belongs_to :note, query_constraints: [:organization_id, :note_id] def belongs_to(name, scope = nil, **options) reflection = Builder::BelongsTo.build(self, name, scope, options) Reflection.add_reflection self, name, reflection end # Specifies a many-to-many relationship with another class. This associates two classes via an # intermediate join table. Unless the join table is explicitly specified as an option, it is # guessed using the lexical order of the class names. So a join between Developer and Project # will give the default join table name of "developers_projects" because "D" precedes "P" alphabetically. # Note that this precedence is calculated using the < operator for String. This # means that if the strings are of different lengths, and the strings are equal when compared # up to the shortest length, then the longer string is considered of higher # lexical precedence than the shorter one. For example, one would expect the tables "paper_boxes" and "papers" # to generate a join table name of "papers_paper_boxes" because of the length of the name "paper_boxes", # but it in fact generates a join table name of "paper_boxes_papers". Be aware of this caveat, and use the # custom :join_table option if you need to. # If your tables share a common prefix, it will only appear once at the beginning. For example, # the tables "catalog_categories" and "catalog_products" generate a join table name of "catalog_categories_products". # # The join table should not have a primary key or a model associated with it. You must manually generate the # join table with a migration such as this: # # class CreateDevelopersProjectsJoinTable < ActiveRecord::Migration[8.0] # def change # create_join_table :developers, :projects # end # end # # It's also a good idea to add indexes to each of those columns to speed up the joins process. # However, in MySQL it is advised to add a compound index for both of the columns as MySQL only # uses one index per table during the lookup. # # Adds the following methods for retrieval and query: # # +collection+ is a placeholder for the symbol passed as the +name+ argument, so # has_and_belongs_to_many :categories would add among others categories.empty?. # # [collection] # Returns a Relation of all the associated objects. # An empty Relation is returned if none are found. # [collection<<(object, ...)] # Adds one or more objects to the collection by creating associations in the join table # (collection.push and collection.concat are aliases to this method). # Note that this operation instantly fires update SQL without waiting for the save or update call on the # parent object, unless the parent object is a new record. # [collection.delete(object, ...)] # Removes one or more objects from the collection by removing their associations from the join table. # This does not destroy the objects. # [collection.destroy(object, ...)] # Removes one or more objects from the collection by running destroy on each association in the join table, overriding any dependent option. # This does not destroy the objects. # [collection=objects] # Replaces the collection's content by deleting and adding objects as appropriate. # [collection_singular_ids] # Returns an array of the associated objects' ids. # [collection_singular_ids=ids] # Replace the collection by the objects identified by the primary keys in +ids+. # [collection.clear] # Removes every object from the collection. This does not destroy the objects. # [collection.empty?] # Returns +true+ if there are no associated objects. # [collection.size] # Returns the number of associated objects. # [collection.find(id)] # Finds an associated object responding to the +id+ and that # meets the condition that it has to be associated with this object. # Uses the same rules as ActiveRecord::FinderMethods#find. # [collection.exists?(...)] # Checks whether an associated object with the given conditions exists. # Uses the same rules as ActiveRecord::FinderMethods#exists?. # [collection.build(attributes = {})] # Returns a new object of the collection type that has been instantiated # with +attributes+ and linked to this object through the join table, but has not yet been saved. # [collection.create(attributes = {})] # Returns a new object of the collection type that has been instantiated # with +attributes+, linked to this object through the join table, and that has already been # saved (if it passed the validation). # [collection.reload] # Returns a Relation of all of the associated objects, forcing a database read. # An empty Relation is returned if none are found. # # ==== Example # # class Developer < ActiveRecord::Base # has_and_belongs_to_many :projects # end # # Declaring has_and_belongs_to_many :projects adds the following methods (and more): # # developer = Developer.find(11) # project = Project.find(9) # # developer.projects # developer.projects << project # developer.projects.delete(project) # developer.projects.destroy(project) # developer.projects = [project] # developer.project_ids # developer.project_ids = [9] # developer.projects.clear # developer.projects.empty? # developer.projects.size # developer.projects.find(9) # developer.projects.exists?(9) # developer.projects.build # similar to Project.new(developer_id: 11) # developer.projects.create # similar to Project.create(developer_id: 11) # developer.projects.reload # # The declaration may include an +options+ hash to specialize the behavior of the association. # # ==== Scopes # # You can pass a second argument +scope+ as a callable (i.e. proc or # lambda) to retrieve a specific set of records or customize the generated # query when you access the associated collection. # # Scope examples: # has_and_belongs_to_many :projects, -> { includes(:milestones, :manager) } # has_and_belongs_to_many :categories, ->(post) { # where("default_category = ?", post.default_category) # } # # ==== Extensions # # The +extension+ argument allows you to pass a block into a # has_and_belongs_to_many association. This is useful for adding new # finders, creators, and other factory-type methods to be used as part of # the association. # # Extension examples: # has_and_belongs_to_many :contractors do # def find_or_create_by_name(name) # first_name, last_name = name.split(" ", 2) # find_or_create_by(first_name: first_name, last_name: last_name) # end # end # # ==== Options # # [+:class_name+] # Specify the class name of the association. Use it only if that name can't be inferred # from the association name. So has_and_belongs_to_many :projects will by default be linked to the # Project class, but if the real class name is SuperProject, you'll have to specify it with this option. # [+:join_table+] # Specify the name of the join table if the default based on lexical order isn't what you want. # WARNING: If you're overwriting the table name of either class, the +table_name+ method # MUST be declared underneath any #has_and_belongs_to_many declaration in order to work. # [+:foreign_key+] # Specify the foreign key used for the association. By default this is guessed to be the name # of this class in lower-case and "_id" suffixed. So a Person class that makes # a #has_and_belongs_to_many association to Project will use "person_id" as the # default :foreign_key. # # Setting the :foreign_key option prevents automatic detection of the association's # inverse, so it is generally a good idea to set the :inverse_of option as well. # [+:association_foreign_key+] # Specify the foreign key used for the association on the receiving side of the association. # By default this is guessed to be the name of the associated class in lower-case and "_id" suffixed. # So if a Person class makes a #has_and_belongs_to_many association to Project, # the association will use "project_id" as the default :association_foreign_key. # [+:validate+] # When set to +true+, validates new objects added to association when saving the parent object. +true+ by default. # If you want to ensure associated objects are revalidated on every update, use +validates_associated+. # [+:autosave+] # If true, always save the associated objects or destroy them if marked for destruction, when # saving the parent object. # If false, never save or destroy the associated objects. # By default, only save associated objects that are new records. # # Note that NestedAttributes::ClassMethods#accepts_nested_attributes_for sets # :autosave to true. # [+:strict_loading+] # Enforces strict loading every time an associated record is loaded through this association. # # Option examples: # has_and_belongs_to_many :projects # has_and_belongs_to_many :projects, -> { includes(:milestones, :manager) } # has_and_belongs_to_many :nations, class_name: "Country" # has_and_belongs_to_many :categories, join_table: "prods_cats" # has_and_belongs_to_many :categories, -> { readonly } # has_and_belongs_to_many :categories, strict_loading: true def has_and_belongs_to_many(name, scope = nil, **options, &extension) habtm_reflection = ActiveRecord::Reflection::HasAndBelongsToManyReflection.new(name, scope, options, self) builder = Builder::HasAndBelongsToMany.new name, self, options join_model = builder.through_model const_set join_model.name, join_model private_constant join_model.name middle_reflection = builder.middle_reflection join_model Builder::HasMany.define_callbacks self, middle_reflection Reflection.add_reflection self, middle_reflection.name, middle_reflection middle_reflection.parent_reflection = habtm_reflection include Module.new { class_eval <<-RUBY, __FILE__, __LINE__ + 1 def destroy_associations association(:#{middle_reflection.name}).delete_all(:delete_all) association(:#{name}).reset super end RUBY } hm_options = {} hm_options[:through] = middle_reflection.name hm_options[:source] = join_model.right_reflection.name [:before_add, :after_add, :before_remove, :after_remove, :autosave, :validate, :join_table, :class_name, :extend, :strict_loading].each do |k| hm_options[k] = options[k] if options.key? k end has_many name, scope, **hm_options, &extension _reflections[name].parent_reflection = habtm_reflection end end end end