ActiveModel Serializer Embedded Associations via ?embed=rel1,rel2

project.rb

class Project < ActiveRecord::Base
  belongs_to :client
  has_many :user_projects
  has_many :users, through: :users_projects
end

project_serializer.rb

class ProjectSerializer < ActiveModel::Serializer
  embed :ids, include: true
  
  attributes :id, :name
  has_one :client
  
  # Has Many
  has_many :user_projects
  has_many :users
  
  # Set to only include if passed (by CSV) in ?embed=
    # Notice how `client` is not included in this loop; `client` will always be embedded
  %w(user_projects users).each do |assoc|
    class_eval <<-RUBY_EVAL, __FILE__, __LINE__+1
      def include_#{assoc}?
        scope[:embed] && scope[:embed].split(','),include?("#{assoc}")
      end 
    RUBY_EVAL
  end
end

projects_controller.rb

class ProjectsController < MyApiBaseController
  serialization_scope :params # Set value of params to the `scope` method in our serializer
  
  inherited_resources # launch le-hack for InheritedResources
  actions :all
  
  def permitted_params
    params.permit project: [:name, :client_id]
  end
end