active_model_serializers/README.md

# ActiveModel::Serializer

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ActiveModel::Serializer brings convention over configuration to your JSON generation.

AMS does this through two components: **serializers** and **adapters**.
Serializers describe _which_ attributes and relationships should be serialized.
Adapters describe _how_ attributes and relationships should be serialized.

By default AMS will use the **Attributes Adapter**. But we strongly advise you to use **JsonApi Adapter** that follows 1.0 of the format specified in [jsonapi.org/format](http://jsonapi.org/format).
Check how to change the adapter in the sections bellow.

# Documentation

Master

- [![API Docs](http://img.shields.io/badge/yard-docs-blue.svg)](http://www.rubydoc.info/github/rails-api/active_model_serializers)
- [Guides](https://github.com/rails-api/active_model_serializers/tree/master/docs)

# RELEASE CANDIDATE, PLEASE READ

This is the master branch of AMS. It will become the `0.10.0` release when it's
ready. Currently this is a release candidate. This is **not** backward
compatible with `0.9.0` or `0.8.0`.

`0.10.x` will be based on the `0.8.0` code, but with a more flexible
architecture. We'd love your help. [Learn how you can help here.](https://github.com/rails-api/active_model_serializers/blob/master/CONTRIBUTING.md)

## Example

Given two models, a `Post(title: string, body: text)` and a
`Comment(name: string, body: text, post_id: integer)`, you will have two
serializers:

```ruby
class PostSerializer < ActiveModel::Serializer
  cache key: 'posts', expires_in: 3.hours
  attributes :title, :body

  has_many :comments
end
```

and

```ruby
class CommentSerializer < ActiveModel::Serializer
  attributes :name, :body

  belongs_to :post
end
```

Generally speaking, you as a user of AMS will write (or generate) these
serializer classes. If you want to use a different adapter, such as a JsonApi, you can
change this in an initializer:

```ruby
ActiveModel::Serializer.config.adapter = ActiveModel::Serializer::Adapter::JsonApi
```

or

```ruby
ActiveModel::Serializer.config.adapter = :json_api
```

You won't need to implement an adapter unless you wish to use a new format or
media type with AMS.

If you want to have a root key on your responses you should use the Json adapter, instead of the default Attributes:

```ruby
ActiveModel::Serializer.config.adapter = :json
```

If you would like the key in the outputted JSON to be different from its name in ActiveRecord, you can use the :key option to customize it:

```ruby
class PostSerializer < ActiveModel::Serializer
  attributes :id, :body

  # look up :subject on the model, but use +title+ in the JSON
  attribute :subject, :key => :title
  has_many :comments
end
```

In your controllers, when you use `render :json`, Rails will now first search
for a serializer for the object and use it if available.

```ruby
class PostsController < ApplicationController
  def show
    @post = Post.find(params[:id])

    render json: @post
  end
end
```

In this case, Rails will look for a serializer named `PostSerializer`, and if
it exists, use it to serialize the `Post`.

### Specify a serializer

If you wish to use a serializer other than the default, you can explicitly pass it to the renderer.

#### 1. For a resource:

```ruby
  render json: @post, serializer: PostPreviewSerializer
```

#### 2. For an array resource:

```ruby
# Use the default `ArraySerializer`, which will use `each_serializer` to
# serialize each element
render json: @posts, each_serializer: PostPreviewSerializer

# Or, you can explicitly provide the collection serializer as well
render json: @posts, serializer: CollectionSerializer, each_serializer: PostPreviewSerializer
```

### Meta

If you want a `meta` attribute in your response, specify it in the `render`
call:

```ruby
render json: @post, meta: { total: 10 }
```

The key can be customized using `meta_key` option.

```ruby
render json: @post, meta: { total: 10 }, meta_key: "custom_meta"
```

`meta` will only be included in your response if you are using an Adapter that supports `root`,
as JsonAPI and Json adapters, the default adapter (Attributes) doesn't have `root`.

### Using a serializer without `render`

At times, you might want to use a serializer without rendering it to the view. For those cases, you can create an instance of `ActiveModel::SerializableResource` with
the resource you want to be serialized and call `.serializable_hash`.

```ruby
def create
  @message = current_user.messages.create!(message_params)
  MessageCreationWorker.perform(serialized_message)
  head 204
end

def serialized_message
  ActiveModel::SerializableResource.new(@message).serializable_hash
end
```

### Overriding association methods

If you want to override any association, you can use:

```ruby
class PostSerializer < ActiveModel::Serializer
  attributes :id, :body

  has_many :comments

  def comments
    object.comments.active
  end
end
```

### Overriding attribute methods

If you want to override any attribute, you can use:

```ruby
class PostSerializer < ActiveModel::Serializer
  attributes :id, :body

  has_many :comments

  def body
    object.body.downcase
  end
end
```

### Built in Adapters

#### Attributes

It's the default adapter, it generates a json response without a root key.
Doesn't follow any specifc convention.

#### JSON

It also generates a json response but always with a root key. The root key **can't be overridden**, and will be automatically defined accordingly with the objects being serialized.
Doesn't follow any specifc convention.

#### JSON API

This adapter follows 1.0 of the format specified in
[jsonapi.org/format](http://jsonapi.org/format). It will include the associated
resources in the `"included"` member when the resource names are included in the
`include` option. Including nested associated resources is also supported.

```ruby
  render @posts, include: ['author', 'comments', 'comments.author']
  # or
  render @posts, include: 'author,comments,comments.author'
```

In addition, two types of wildcards may be used. `*` includes one level of associations, and `**` includes all recursively. These can be combined with other paths.

```ruby
  render @posts, include: '**' # or '*' for a single layer
```

The following would render posts and include the author, the author's comments, and every resource referenced by the author's comments (recursively). It could be combined, like above, with other paths in any combination desired.

```ruby
  render @posts, include: 'author.comments.**'
```

The JSON API [specifies](http://jsonapi.org/format/#fetching-includes) that the user may supply a parameter specifying which related resources are to be included:

```ruby
  render @posts, include: params[:include]
```

This raises some security concerns since the user could pass in `include=**`, so filter the values for `include` appropriately if you decide to support this JSON API feature.

## Installation

Add this line to your application's Gemfile:

```
gem 'active_model_serializers'
```

And then execute:

```
$ bundle
```

## Creating a Serializer

The easiest way to create a new serializer is to generate a new resource, which
will generate a serializer at the same time:

```
$ rails g resource post title:string body:string
```

This will generate a serializer in `app/serializers/post_serializer.rb` for
your new model. You can also generate a serializer for an existing model with
the serializer generator:

```
$ rails g serializer post
```

The generated seralizer will contain basic `attributes` and
`has_many`/`has_one`/`belongs_to` declarations, based on the model. For example:

```ruby
class PostSerializer < ActiveModel::Serializer
  attributes :title, :body

  has_many :comments
  has_one :author
end
```

and

```ruby
class CommentSerializer < ActiveModel::Serializer
  attributes :name, :body

  belongs_to :post_id
end
```

The attribute names are a **whitelist** of attributes to be serialized.

The `has_many`, `has_one`, and `belongs_to` declarations describe relationships between
resources. By default, when you serialize a `Post`, you will get its `Comments`
as well.

You may also use the `:serializer` option to specify a custom serializer class, for example:

```ruby
  has_many :comments, serializer: CommentPreviewSerializer
```

And you can change the JSON key that the serializer should use for a particular association:

```ruby
  has_many :comments, key: :reviews
```

## Pagination

Pagination links will be included in your response automatically as long
as the resource is paginated using [Kaminari](https://github.com/amatsuda/kaminari) or
[WillPaginate](https://github.com/mislav/will_paginate) and
if you are using the ```JsonApi``` adapter.

Although the others adapters does not have this feature, it is possible to
implement pagination links to `JSON` adapter. For more information about it,
please see in our docs [How to add pagination
links](https://github.com/rails-api/active_model_serializers/blob/master/docs/howto/add_pagination_links.md).

## Caching

To cache a serializer, call ```cache``` and pass its options.
The options are the same options of ```ActiveSupport::Cache::Store```, plus
a ```key``` option that will be the prefix of the object cache
on a pattern ```"#{key}/#{object.id}-#{object.updated_at}"```.

The cache support is optimized to use the cached object in multiple request. An object cached on a ```show``` request will be reused at the ```index```. If there is a relationship with another cached serializer it will also be created and reused automatically.

**[NOTE] Every object is individually cached.**

**[NOTE] The cache is automatically expired after an object is updated, but it's not deleted.**

```ruby
cache(options = nil) # options: ```{key, expires_in, compress, force, race_condition_ttl}```
```

Take the example bellow:

```ruby
class PostSerializer < ActiveModel::Serializer
  cache key: 'post', expires_in: 3.hours
  attributes :title, :body

  has_many :comments
end
```

On this example every ```Post``` object will be cached with
the key ```"post/#{post.id}-#{post.updated_at}"```. You can use this key to expire it as you want,
but in this case it will be automatically expired after 3 hours.

### Fragment Caching

If there is some API endpoint that shouldn't be fully cached, you can still optimise it, using Fragment Cache on the attributes and relationships that you want to cache.

You can define the attribute by using ```only``` or ```except``` option on cache method.

**[NOTE] Cache serializers will be used at their relationships**

Example:

```ruby
class PostSerializer < ActiveModel::Serializer
  cache key: 'post', expires_in: 3.hours, only: [:title]
  attributes :title, :body

  has_many :comments
end
```

## Getting Help

If you find a bug, please report an [Issue](https://github.com/rails-api/active_model_serializers/issues/new).

If you have a question, please [post to Stack Overflow](http://stackoverflow.com/questions/tagged/active-model-serializers).

Thanks!

# Contributing

See [CONTRIBUTING.md](https://github.com/rails-api/active_model_serializers/blob/master/CONTRIBUTING.md)