Now an user can add subjects separately

app/controllers/concerns/subjectable_controller.rb

+module SubjectableController
+  extend ActiveSupport::Concern
+
+  included do
+    before_action :authenticate_user!, only: [:subjecting, :unsubjecting]
+  end
+
+    # POST /v1/learning_objects/1/subjects
+    # POST /v1/learning_objects/1/subjects.json
+    def subjecting
+      subjectable.add_subjects(ids: params[:subjects])
+      render json: subjectable.subjects, status: :created
+    end
+
+    # DELETE /v1/learning_objects/1/subjects
+    # DELETE /v1/learning_objects/1/subjects.json
+    #def unsubjecting
+    #  @owner.remove_subjects(subject_params[:id])
+    #  render json: subjects.tags, status: :ok
+    #end
+
+    protected
+
+    def subjectable
+      raise NotImplementedError
+    end
+
+end

app/controllers/v1/learning_objects_controller.rb

@@ -6,11 +6,12 @@ class V1::LearningObjectsController < ApplicationController
   include ::Paginator
   include ::DeletedObjectsController
   include ::HighlightsController
+  include ::SubjectableController
 
   before_action :authenticate_user!, except: [:create, :index, :show]
   before_action :set_learning_object, only: [:show, :update, :destroy]
   before_action :set_new_learning_object, only: :index
-  before_action :authorize!, except: [:create, :tagging, :untagging]
+  before_action :authorize!, except: [:create, :tagging, :untagging, :subjecting, :unsubjecting]
 
   def index
     learning_objects = paginate LearningObject.includes(:tags, :publisher, :language, :license, :subjects, :educational_stages, :reviews)
@@ -69,6 +70,7 @@ class V1::LearningObjectsController < ApplicationController
   def highlights_resource; LearningObject; end
   def sociable; set_learning_object; end
   def taggable; set_learning_object; end
+  def subjectable; set_learning_object; end
 
   # Use callbacks to share common setup or constraints between actions.
   def set_learning_object