How to implement multiple different serializers for same model using ActiveModel::Serializers?

Question

Let's say you're implementing a REST API in Rails. When serving a collection, you might want to only include a few attributes:

/people

But when serving a single resource, you want to include all the attributes:

/people/1

I don't see how to do that using ActiveModel::Serializers, since the examples all use the pattern of defining one serializer per model (with a standard naming convention) and having AMS automatically use the right one in the controller when you do:

render json: @people

or:

render json: @person

Answer 1

You can have multiple serializers for the same model, e.g.

class SimplePersonSerializer < ActiveModel::Serializer
  attributes :id, :name
end

and

class CompletePersonSerializer < ActiveModel::Serializer
  attributes :id, :name, :phone, :email
end

simple info for people in one controller:

render json: @people, each_serializer: SimplePersonSerializer

complete info for people in another:

render json: @people, each_serializer: CompletePersonSerializer

simple info for a single person:

render json: @person, serializer: SimplePersonSerializer

complete info for a single person:

render json: @person, serializer: CompletePersonSerializer

Answer 2

class CompletePersonSerializer < ActiveModel::Serializer
  root :person
  attributes :id, :name, :phone, :email
end

or

render json: @people, each_serializer: CompletePersonSerializer, root: :person

Answer 3

To avoid mixing view concerns into your models (via serialized variations), use the view to render your JSON for each action, much like we do for HTML.

jbuilder & rabl both fill this data templating need quite nicely.

Update 2013-12-16: The ActiveModelSerializers library does support defining multiple serializers for one model, as @phaedryx answered later, by using custom serializers.