# ActiveModelSerializers

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## About ActiveModelSerializers brings convention over configuration to your JSON generation. ActiveModelSerializers works through two components: **serializers** and **adapters**. Serializers describe _which_ attributes and relationships should be serialized. Adapters describe _how_ attributes and relationships should be serialized. SerializableResource co-ordinates the resource, Adapter and Serializer to produce the resource serialization. The serialization has the `#as_json`, `#to_json` and `#serializable_hash` methods used by the Rails JSON Renderer. (SerializableResource actually delegates these methods to the adapter.) By default ActiveModelSerializers will use the **Attributes Adapter** (no JSON root). But we strongly advise you to use **JsonApi Adapter**, which follows 1.0 of the format specified in [jsonapi.org/format](http://jsonapi.org/format). Check how to change the adapter in the sections below. `0.10.x` is **not** backward compatible with `0.9.x` nor `0.8.x`. `0.10.x` is based on the `0.8.0` code, but with a more flexible architecture. We'd love your help. [Learn how you can help here.](CONTRIBUTING.md) It is generally safe and recommended to use the master branch. ## Installation Add this line to your application's Gemfile: ``` gem 'active_model_serializers', '~> 0.10.0' ``` And then execute: ``` $ bundle ``` ## Getting Started See [Getting Started](docs/general/getting_started.md) for the nuts and bolts. More information is available in the [Guides](docs) and [High-level behavior](README.md#high-level-behavior). ## Getting Help If you find a bug, please report an [Issue](https://github.com/rails-api/active_model_serializers/issues/new) and see our [contributing guide](CONTRIBUTING.md). If you have a question, please [post to Stack Overflow](http://stackoverflow.com/questions/tagged/active-model-serializers). If you'd like to chat, we have a [community slack](http://amserializers.herokuapp.com). Thanks! ## Documentation If you're reading this at https://github.com/rails-api/active_model_serializers you are reading documentation for our `master`, which may include features that have not been released yet. Please see below for the documentation relevant to you. - [0.10 (master) Documentation](https://github.com/rails-api/active_model_serializers/tree/master) - [0.10.6 (latest release) Documentation](https://github.com/rails-api/active_model_serializers/tree/v0.10.6) - [![API Docs](http://img.shields.io/badge/yard-docs-blue.svg)](http://www.rubydoc.info/gems/active_model_serializers/0.10.6) - [Guides](docs) - [0.9 (0-9-stable) Documentation](https://github.com/rails-api/active_model_serializers/tree/0-9-stable) - [![API Docs](http://img.shields.io/badge/yard-docs-blue.svg)](http://www.rubydoc.info/github/rails-api/active_model_serializers/0-9-stable) - [0.8 (0-8-stable) Documentation](https://github.com/rails-api/active_model_serializers/tree/0-8-stable) - [![API Docs](http://img.shields.io/badge/yard-docs-blue.svg)](http://www.rubydoc.info/github/rails-api/active_model_serializers/0-8-stable) ## High-level behavior Choose an adapter from [adapters](lib/active_model_serializers/adapter): ``` ruby ActiveModelSerializers.config.adapter = :json_api # Default: `:attributes` ``` Given a [serializable model](lib/active_model/serializer/lint.rb): ```ruby # either class SomeResource < ActiveRecord::Base # columns: title, body end # or class SomeResource < ActiveModelSerializers::Model attributes :title, :body end ``` And initialized as: ```ruby resource = SomeResource.new(title: 'ActiveModelSerializers', body: 'Convention over configuration') ``` Given a serializer for the serializable model: ```ruby class SomeSerializer < ActiveModel::Serializer attribute :title, key: :name attributes :body end ``` The model can be serialized as: ```ruby options = {} serialization = ActiveModelSerializers::SerializableResource.new(resource, options) serialization.to_json serialization.as_json ``` SerializableResource delegates to the adapter, which it builds as: ```ruby adapter_options = {} adapter = ActiveModelSerializers::Adapter.create(serializer, adapter_options) adapter.to_json adapter.as_json adapter.serializable_hash ``` The adapter formats the serializer's attributes and associations (a.k.a. includes): ```ruby serializer_options = {} serializer = SomeSerializer.new(resource, serializer_options) serializer.attributes serializer.associations ``` ## Architecture This section focuses on architecture the 0.10.x version of ActiveModelSerializers. If you are interested in the architecture of the 0.8 or 0.9 versions, please refer to the [0.8 README](https://github.com/rails-api/active_model_serializers/blob/0-8-stable/README.md) or [0.9 README](https://github.com/rails-api/active_model_serializers/blob/0-9-stable/README.md). The original design is also available [here](https://github.com/rails-api/active_model_serializers/blob/d72b66d4c5355b0ff0a75a04895fcc4ea5b0c65e/README.textile). ### ActiveModel::Serializer An **`ActiveModel::Serializer`** wraps a [serializable resource](https://github.com/rails/rails/blob/4-2-stable/activemodel/lib/active_model/serialization.rb) and exposes an `attributes` method, among a few others. It allows you to specify which attributes and associations should be represented in the serializatation of the resource. It requires an adapter to transform its attributes into a JSON document; it cannot be serialized itself. It may be useful to think of it as a [presenter](http://blog.steveklabnik.com/posts/2011-09-09-better-ruby-presenters). #### ActiveModel::CollectionSerializer The **`ActiveModel::CollectionSerializer`** represents a collection of resources as serializers and, if there is no serializer, primitives. ### ActiveModelSerializers::Adapter::Base The **`ActiveModelSerializeres::Adapter::Base`** describes the structure of the JSON document generated from a serializer. For example, the `Attributes` example represents each serializer as its unmodified attributes. The `JsonApi` adapter represents the serializer as a [JSON API](http://jsonapi.org/) document. ### ActiveModelSerializers::SerializableResource The **`ActiveModelSerializers::SerializableResource`** acts to coordinate the serializer(s) and adapter to an object that responds to `to_json`, and `as_json`. It is used in the controller to encapsulate the serialization resource when rendered. However, it can also be used on its own to serialize a resource outside of a controller, as well. ### Primitive handling Definitions: A primitive is usually a String or Array. There is no serializer defined for them; they will be serialized when the resource is converted to JSON (`as_json` or `to_json`). (The below also applies for any object with no serializer.) - ActiveModelSerializers doesn't handle primitives passed to `render json:` at all. Internally, if no serializer can be found in the controller, the resource is not decorated by ActiveModelSerializers. - However, when a primitive value is an attribute or in a collection, it is not modified. When serializing a collection and the collection serializer (CollectionSerializer) cannot identify a serializer for a resource in its collection, it throws [`:no_serializer`](https://github.com/rails-api/active_model_serializers/issues/1191#issuecomment-142327128). For example, when caught by `Reflection#build_association`, and the association value is set directly: ```ruby reflection_options[:virtual_value] = association_value.try(:as_json) || association_value ``` (which is called by the adapter as `serializer.associations(*)`.) ### How options are parsed High-level overview: - For a **collection** - `:serializer` specifies the collection serializer and - `:each_serializer` specifies the serializer for each resource in the collection. - For a **single resource**, the `:serializer` option is the resource serializer. - Options are partitioned in serializer options and adapter options. Keys for adapter options are specified by [`ADAPTER_OPTION_KEYS`](https://github.com/rails-api/active_model_serializers/blob/master/lib/active_model_serializers/serializable_resource.rb#L5). The remaining options are serializer options. Details: 1. **ActionController::Serialization** 1. `serializable_resource = ActiveModelSerializers::SerializableResource.new(resource, options)` 1. `options` are partitioned into `adapter_opts` and everything else (`serializer_opts`). The `adapter_opts` keys are defined in [`ActiveModelSerializers::SerializableResource::ADAPTER_OPTION_KEYS`](lib/active_model_serializers/serializable_resource.rb#L5). 1. **ActiveModelSerializers::SerializableResource** 1. `if serializable_resource.serializer?` (there is a serializer for the resource, and an adapter is used.) - Where `serializer?` is `use_adapter? && !!(serializer)` - Where `use_adapter?`: 'True when no explicit adapter given, or explicit value is truthy (non-nil); False when explicit adapter is falsy (nil or false)' - Where `serializer`: 1. from explicit `:serializer` option, else 2. implicitly from resource `ActiveModel::Serializer.serializer_for(resource)` 1. A side-effect of checking `serializer` is: - The `:serializer` option is removed from the serializer_opts hash - If the `:each_serializer` option is present, it is removed from the serializer_opts hash and set as the `:serializer` option 1. The serializer and adapter are created as 1. `serializer_instance = serializer.new(resource, serializer_opts)` 2. `adapter_instance = ActiveModel::Serializer::Adapter.create(serializer_instance, adapter_opts)` 1. **ActiveModel::Serializer::CollectionSerializer#new** 1. If the `serializer_instance` was a `CollectionSerializer` and the `:serializer` serializer_opts is present, then [that serializer is passed into each resource](https://github.com/rails-api/active_model_serializers/blob/a54d237e2828fe6bab1ea5dfe6360d4ecc8214cd/lib/active_model/serializer/array_serializer.rb#L14-L16). 1. **ActiveModel::Serializer#attributes** is used by the adapter to get the attributes for resource as defined by the serializer. (In Rails, the `options` are also passed to the `as_json(options)` or `to_json(options)` methods on the resource serialization by the Rails JSON renderer. They are, therefore, important to know about, but not part of ActiveModelSerializers.) ### What does a 'serializable resource' look like? - An `ActiveRecord::Base` object. - Any Ruby object that passes the [Lint](http://www.rubydoc.info/github/rails-api/active_model_serializers/ActiveModel/Serializer/Lint/Tests) [code](https://github.com/rails-api/active_model_serializers/blob/master/lib/active_model/serializer/lint.rb). ActiveModelSerializers provides a [`ActiveModelSerializers::Model`](https://github.com/rails-api/active_model_serializers/blob/master/lib/active_model_serializers/model.rb), which is a simple serializable PORO (Plain-Old Ruby Object). `ActiveModelSerializers::Model` may be used either as a reference implementation, or in production code. ```ruby class MyModel < ActiveModelSerializers::Model attributes :id, :name, :level end ``` The default serializer for `MyModel` would be `MyModelSerializer` whether MyModel is an ActiveRecord::Base object or not. Outside of the controller the rules are **exactly** the same as for records. For example: ```ruby render json: MyModel.new(level: 'awesome'), adapter: :json ``` would be serialized the same as ```ruby ActiveModelSerializers::SerializableResource.new(MyModel.new(level: 'awesome'), adapter: :json).as_json ``` ## Semantic Versioning This project adheres to [semver](http://semver.org/) ## Contributing See [CONTRIBUTING.md](CONTRIBUTING.md)