gistfile1.js

// this is my goal JSON output

{
  post:{
    ...
    comments: [1,2,3]
  },
  comments:[{
    comment:{
      ...
      author_id: 1
    }
  }]
  authors:[{
    author:{
      id: 1
    }
  }]
}

gistfile2.rb

# CONTROLLER

class PostsController < ..
    
    def show
        @post = Post.find(1)
        render json: @post
    end
end

# Base Serializer
class BaseSerializer < ..
    embed :ids, include: true
end

# Post Serializer
class PostSerializer < BaseSerializer
    attributes :id, ...
    
    has_many :comments
end

# Comment Serializer
class CommentSerializer < BaseSerializer
    attributes :id, :text ...
    
    # by including this relationship I am getting
    # no implicit conversion of String into Integer
    # if I remove it, the error goes away
    has_one :author
end