# ActiveRecordSchema

**ActiveRecordSchema** is an `ActiveRecord` extension that allows you to write database schema for a model within the model itself and to generate migrations directly from models.

Unlike other libraries (eg. mini_record) ActiveRecordSchema is not an alternative to Rails migrations, but rather a tool to simplify their use.

## Features

* Defining columns and indexes directly in model
* Generation of migration from the model taking into account the current state of the database
* Automatically add code to migrate associations:
   * Foreign key for `belongs_to`
   * Join table for `has_and_belongs_to_many`
  
* Automatic indexing of foreign keys for both `belongs_to` and `has_and_belongs_to_many` (configurable)

## Installation

Put this in your Gemfile

    gem 'active_record_schema'
    
and update your bundle
  
    bundle install
    
**NOTE:** ActiveRecordSchema depends on `rails ~> 3.0` and not only `ActiveRecord`

## Configuration

In order to correctly solve the required fields for the inheritance ActiveRecordSchema requires that all classes of models are loaded in memory when generating migration. This is done by pre-loading models in the generator. To figure out which file to load ARS refers to the global configuration property in `ActiveRecordSchema.config.autoload_paths` that is set by default to:

``` rb
[
   Rails.root.join('app', 'models', '*.rb'),
   Rails.root.join('app', 'models', '**', '*.rb') 
]
```

You can change this by creating an initializer and setting or appending new paths to `ActiveRecordSchema.config.autoload_paths`


``` rb
# active_record_schema_initializer.rb
ActiveRecordSchema.config.autoload_paths << Rails.root.join('lib', 'models', '*.rb')
```


## Usage

Create a model and use the class method `#field` to define columns

``` rb    
class Post < ActiveRecord::Base
    field :title
    field :body, :as => :text
    belongs_to :author, :class_name => "User"
end
```

Now run `rails g migration` with `--from` option

    rails g migration init_posts_schema --from Post
  
and the following migration will be generated

``` rb    
class InitPostsSchema < ActiveRecord::Migration
  def change
    create_table :posts 
    add_column :posts, :title, :string
    add_column :posts, :body, :text

    add_column :author_id, :integer
    index :author_id
  end
end
```

**NOTE:** `create_table :posts` is added only if `posts` table does not exist yet

Generating a migration for new columns is the same, lets add a new field to `Post` (eg. `pubdate`):

``` rb    
class Post < ActiveRecord::Base
    field :title
    field :body, :as => :text
    belongs_to :author, :class_name => "User"
    
    field :pubdate, :as => :datetime
end
```

Now run

    rails g migration add_pubdate_to_posts --from Post

that will generate:

``` rb
class AddPubdateToPosts < ActiveRecord::Migration
  def change
    add_column :posts, :pubdate, :datetime
  end
end
```

**NOTE:** No migration will be generated in case all changes are up-to-date 

## Has and Belongs To Many (HBTM) associations

Lets try to add a HBTM association to our `Post` model

_ex._

``` rb
# post.rb
class Post < ActiveRecord::Base
  field :title
  field :body, :as => :text
  belongs_to :author, :class_name => "User"
  field :pubdate, :as => :datetime

  has_and_belongs_to_many :voters, :class_name => "User"
end
```


Now running

    rails g migration add_voters_to_posts --from Post

will generate:

``` rb
class AddVotersToPosts < ActiveRecord::Migration
  def change
    create_table :posts_users, :id => false do |t|
      t.integer  "post_id"
      t.integer  "user_id"
    end
    add_index :posts_users, "post_id"
    add_index :posts_users, "user_id"
  end
end
```

## Single Table Inheritance (STI)

Call `#inheritable` inside the base class of your hierarchy to add the inheritance column required by Single Table Inheritance.

_ex._

``` rb
# content.rb
class Content < ActiveRecord::Base
  inheritable
  
  field :title
  
  has_and_belongs_to_many :voters, :class_name => "User"
  belongs_to              :author, :class_name => "User"
    
  timestamps
end
    
  
# article.rb
class Article < Content
  field :body, :as => :text
end
    
  
# video.rb
class Video < Content
  field :url
end
```

Running
    
    rails g migration init_contents --from Content

same as

    rails g migration init_contents --from Article
    
same as

    rails g migration init_contents --from Video
    
will generate the following migration 

``` rb
class InitContents < ActiveRecord::Migration
  def change
    add_column :contents, :type, :string
    add_column :contents, :title, :string
    add_column :contents, :author_id, :string
    add_column :contents, :body, :text
    add_column :contents, :url, :string

    add_index :contents, :author_id

    create_table :contents_users, :id => false do |t|
      t.integer  "content_id"
      t.integer  "user_id"
    end
    add_index :contents_users, "content_id"
    add_index :contents_users, "user_id"
  end  
end
```


## Mixins

Probably one of the most significant advantage given by ActiveRecordSchema is to allow the definition of fields in modules and reuse them through mixins

_ex._

``` rb
module Profile
  extend ActiveSupport::Concern
  included do
    field :name
    field :age, :as => :integer
      
  end
end
    
class User < ActiveRecord::Base
  include Profile
  
end
    
class Player < ActiveRecord::Base
  include Profile
      
end
```


## DSL (Domain Specific Language) reference

  * ### `field(name, *args)`

    Adds a new column with name `name` to the schema. The type of column can be passed either as second argument or as option, if not specified is intended to be `:string`

    #### options  

    * **:as** _or_ **:type** : Specify the type of the column. The value can be a `String`, a `Symbol` or a `Class`, default to `:string`
    * **:index** : Specify wether or not the field should be indexed, default to `false`

    #### examples

    ``` rb
    field :name

    field :name, :string
    field :name, "string"
    field :name, String

    field :name, :as => :string
    field :name, :as => "string"
    field :name, :as => String

    field :name, :type => :string
    field :name, :type => "string"
    field :name, :type => String

    field :age, :as => :integer, :index => true
    ```


  * ### `belongs_to(name, options = {})`

    Adds a new foreign key column for the association to the schema and then delegates to `ActiveRecord::Base.belongs_to`. If the association is polymorphic a column for foreign type is also generated.

    #### options  

    * **:index** : Specify wether or not the foreing key column should be indexed, default to `true`. If the association is polymorphic creates an index on both foreign key and foreing type


  * ### `has_and_belongs_to_many(name, options = {}, &extension)`

    Adds a new join table for the association to the schema and then delegates to `ActiveRecord::Base.has_and_belongs_to_many`

  * ### `index(column_name, options = {})`

    Adds a new index for `column_name` column to the schema
    
  * ### `add_index(column_name, options = {})`

    alias for `index`

  * ### `timestamps`

    Same as

    ``` rb
    field :created_at, :datetime
    field :updated_at, :datetime
    ```

  * ### `inheritable`
  
    Same as

    ``` rb
    field :"#{inheritance_column}"
    ```


## Why do not also generate irreversible changes (change/remove columns or indexes)?

ActiveRecordSchema does not take into account the removal of columns and indexes or changes in the types of columns. The reason for this is that these changes are not reversible, so it's a better idea to introduce them by hand rather than let them be generated automatically. Anyway the need to resort to harsh measures such as irreversible changes is limited to non-routine situations.


## Contributing to active_record_schema
 
* Check out the latest master to make sure the feature hasn't been implemented or the bug hasn't been fixed yet.
* Check out the issue tracker to make sure someone already hasn't requested it and/or contributed it.
* Fork the project.
* Start a feature/bugfix branch.
* Commit and push until you are happy with your contribution.
* Make sure to add tests for it. This is important so I don't break it in a future version unintentionally.
* Please try not to mess with the Rakefile, version, or history. If you want to have your own version, or is otherwise necessary, that is fine, but please isolate to its own commit so I can cherry-pick around it.

---

Copyright (c) 2012 mcasimir

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