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

Alonaalone

Answer 1

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.

Diskson

So, what you're saying is that AMS doesn't yet have the flexibility in it's current design to satisfy this common use case of differently serializing for different API responses? Because that's how it feels, but I didn't want to assume the problem wasn't simply my own ignorance, especially since AMS is being considered for Rails4 core as "the way"... – Alonaalone

jbuilder was created by DHH specifically to address this problem in Rails. Creating variations via ActiveModel::Serializers will end up putting public-API (view) concerns in your controllers &/or models. – Diskson

Ok. Obviously I need to look at jbuilder and then decide how to proceed, but it was a good answer. Thanks! – Alonaalone

Answer 2

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

Figurate

How can I have the key as person: {} not complete_person: {}? – Virginity

@chopper yes. you just need to append root: :person. Here is a full example render json: @person, serializer: CompletePersonSerializer, root: :person – Virginity

You can subclass class CompletePersonSerializer < SimplePersonSerializer and include just the new attributes – Grearson

@SeifSallam You can add the root: person to the serializer class it self. It doesn't need be specified everywhere you call render json – Penman

Phaedryx and @Swards you guys are my heroes! – Elvinelvina

Is there any way to specify this for each action automatically at the controller level? – Asyndeton

it would be very handy to change this to the answer. – Cogan

Answer 3

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

or

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

Chalkboard

as of today, root :person raises an error. each_serializer: CompletePersonSerializer is sufficient – Repulsive

Answer 4

Adding to what @phaedryx said, what I do for this is call a method that returns the correct serializer... for your question, I'd use:

class MyController < ApplicationController

  def index
    render json: @people, each_serializer: serializer_method
  end

  private

  def serializer_method
    defined?(@people) ? PeopleSerializer : PersonSerializer
  end

end

Filipino

Answer 5

IMO it's best to have a specific serializer for each controller action. I built this concern to handle it. (which I add to base controller)

module Serializable
  extend ActiveSupport::Concern

   alias each_serializer serializer

   def serializer
     "#{params[:controller].classify}s::#{params[:action].classify}Serializer".constantize
   end
end

That way you can just call

render json: @person, serializer:

in your controller and it will find the correct serializer.

Reynaldoreynard