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# Rendering

### Implicit Serializer

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`.

### Explicit 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 a resource collection:

Specify the serializer for each resource with `each_serializer`

```ruby
render json: @posts, each_serializer: PostPreviewSerializer
```

The default serializer for collections is `CollectionSerializer`.

Specify the collection serializer with the `serializer` option.

```ruby
render json: @posts, serializer: CollectionSerializer, each_serializer: PostPreviewSerializer
```

## Serializing non-ActiveRecord objects

All serializable resources must pass the
[ActiveModel::Serializer::Lint::Tests](../../lib/active_model/serializer/lint.rb#L17).

See the ActiveModelSerializers::Model for a base class that implements the full
API for a plain-old Ruby object (PORO).

## SerializableResource options

The `options` hash passed to `render` or `ActiveModel::SerializableResource.new(resource, options)`
are partitioned into `serializer_opts` and `adapter_opts`. `adapter_opts` are passed to new Adapters;
`serializer_opts` are passed to new Serializers.

The `adapter_opts` are specified in [ActiveModel::SerializableResource::ADAPTER_OPTIONS](../../lib/active_model/serializable_resource.rb#L4).
The `serializer_opts` are the remaining options.

(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.)

See [ARCHITECTURE](../ARCHITECTURE.md) for more information.

### adapter_opts

#### fields

PR please :)

#### adapter

PR please :)

#### key_transform

```render json: posts, each_serializer: PostSerializer, key_transform: :camel_lower```

See [Key Transforms](key_transforms.md) for more informaiton.

#### meta

A `meta` member can be used to include non-standard meta-information. `meta` can
be utilized in several levels in a response.

##### Top-level

To set top-level `meta` in a 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`, e.g., `JsonApi` and `Json` adapters. The default adapter,
`Attributes` does not have `root`.


##### Resource-level

To set resource-level `meta` in a response, define meta in a serializer with one
of the following methods:

As a single, static string.

```ruby
meta stuff: 'value'
```

As a block containing a Hash.

```ruby
meta do
  {
    rating: 4,
    comments_count: object.comments.count
  }
end
```


#### links

If you wish to use Rails url helpers for link generation, e.g., `link(:resources) { resources_url }`, ensure your application sets
`Rails.application.routes.default_url_options`.

##### Top-level

JsonApi supports a [links object](http://jsonapi.org/format/#document-links) to be specified at top-level, that you can specify in the `render`:

```ruby
  links_object = {
    href: "http://example.com/api/posts",
    meta: {
      count: 10
    }
  }
  render json: @posts, links: links_object
```

That's the result:

```json
{
  "data": [
    {
      "type": "posts",
      "id": "1",
      "attributes": {
        "title": "JSON API is awesome!",
        "body": "You should be using JSON API",
        "created": "2015-05-22T14:56:29.000Z",
        "updated": "2015-05-22T14:56:28.000Z"
      }
    }
  ],
  "links": {
    "href": "http://example.com/api/posts",
    "meta": {
      "count": 10
    }
  }
}
```

This feature is specific to JsonApi, so you have to use the use the [JsonApi Adapter](adapters.md#jsonapi)


##### Resource-level

In your serializer, define each link in one of the following methods:

As a static string

```ruby
link :link_name, 'https://example.com/resource'
```

As a block to be evaluated. When using Rails, URL helpers are available.
Ensure your application sets `Rails.application.routes.default_url_options`.

```ruby
link :link_name_ do
  "https://example.com/resource/#{object.id}"
end

link(:link_name) { "https://example.com/resource/#{object.id}" }

link(:link_name) { resource_url(object) }

link(:link_name) { url_for(controller: 'controller_name', action: 'index', only_path: false) }

```

### serializer_opts

#### include

PR please :)

#### root

The resource root is derived from the class name of the resource being serialized.
e.g. `UserPostSerializer.new(UserPost.new)` will be serialized with the root `user_post` or `user_posts` according the adapter collection pluralization rules.

Specify the root by passing it as an argument to `render`. For example:

```ruby
  render json: @user_post, root: "admin_post", adapter: :json
```

This will be rendered as:
```json
  {
    "admin_post": {
      "title": "how to do open source"
    }
  }
```
Note: the `Attributes` adapter (default) does not include a resource root.

#### serializer

PR please :)

#### scope

PR please :)

#### scope_name

PR please :)

## Using a serializer without `render`

See [Usage outside of a controller](../howto/outside_controller_use.md#serializing-before-controller-render).

## Pagination

See [How to add pagination links](https://github.com/rails-api/active_model_serializers/blob/master/docs/howto/add_pagination_links.md).