Active Model Serializer not working with json_api adapter - ruby-on-rails

Question

I am trying to use custom serializers for the relationships in a serializer and the json_api adapter enabled. However the relationships are not serialized correctly (or, better, not at all displayed/serialized).
PostController.rb
def index
render json: Post.all, each_serializer: Serializers::PostSerializer
end
Serializer
module Api
module V1
module Serializers
class PostSerializer < ActiveModel::Serializer
attributes :title, :id
belongs_to :author, serializer: UserSerializer
has_many :post_sections, serializer: PostSectionSerializer
end
end
end
end
JSON output:
{
"data": [
{
"attributes": {
"title": "Test Title"
},
"id": "1",
"relationships": {
"author": {
"data": {
"id": "1",
"type": "users"
}
},
"post_sections": {
"data": [
{
"id": "1",
"type": "post_sections"
}
]
}
},
"type": "posts"
}
]
}
As you can see, the relationships are not fulfilled, which happens only if I specify a custom serializer for the relationships!!
If I do something like this:
module Api
module V1
module Serializers
class PostSerializer < ActiveModel::Serializer
attributes :title, :id
belongs_to :author # no custom serializer!
has_many :post_sections # no custom serializer!
end
end
end
end
The relationships are shown correctly, but not using a custom serializer...
What's the issue here ?
EDIT
According to the json API 1.0 Format, what I am getting back is the so-called resource identifier object.
The following primary data is a single resource identifier object that
references the same resource:
{ "data": {
"type": "articles",
"id": "1" } }
Is there a way to prevent getting resource identifier objects, and get the actual data instead ?

Answer 1

Relationships only returns id and type according to json-api exmaples. If you need to return more information about this relation you should add include option on your render action.
Ex.
PostController.rb
class PostsController < ApplicationController
def show
render json: #post, include: 'comments'
end
end
Serializers
class PostSerializer < ActiveModel::Serializer
attributes :id, :title, :content
has_many :comment, serializer: CommentSerializer
end
class CommentSerializer < ActiveModel::Serializer
attributes :id, :title, :content
end
JSON output:
{
"data": {
"id": "1",
"type": "post",
"attributes": {
"title": "bla",
"content": "bla"
},
"relationships": {
"comment": {
"data": [
{
"type": "comments",
"id": "1"
}
]
}
}
},
"included": {
{
"id": "1",
"type": "comments",
"attributes": {
"title": "test",
"content": "test"
}
}
]
}

Answer 2

Just to add to #Bruno Bacarini's answer, you may also include chained associations by using:
render #posts, include: ['authors.profile', 'comments']
source: joaomdmoura's comment on github