add method for find collections of a learning object and rendering json

app/controllers/learning_objects_controller.rb

 class LearningObjectsController < ApplicationController
-  before_action :set_learning_object, only: [:show, :edit, :update, :destroy, :like, :bookmark]
+  before_action :set_learning_object, only: [:show, :edit, :update, :destroy, :like, :bookmarks, :collections]
   after_action :increment_learning_object_views, only: [:show]
   before_action :authenticate_user!, except: [:index, :show, :like]
   before_action :set_complaint_messages, only: :show
@@ -88,6 +88,11 @@ class LearningObjectsController < ApplicationController
     end
   end
 
+  # GET /learning_objects/1/collections.json
+  def collections
+    @collections = @learning_object.collections
+  end
+
   private
 
   # Use callbacks to share common setup or constraints between actions.

app/models/learning_object.rb

@@ -16,6 +16,10 @@ class LearningObject
     super(params.merge(defaults))
   end
 
+  def collections
+    collection_repository.find_by_learning_object self
+  end
+
   def like(user)
     learning_object_repository.like user, self
   end

app/repositories/orient_db/collection_repository.rb

@@ -43,7 +43,16 @@ module OrientDb
 
     def all(user)
       query = sprintf("select * from (select expand(in('BelongsTo')) from %s) where name<>'Bookmarks'", user.rid)
-      objects = build_objects connection.query(query)
+      build_objects connection.query(query)
+    end
+
+    def find_by_learning_object(learning_object)
+      if learning_object.id.to_s.empty?
+        return []
+      end
+
+      query = sprintf("select * from %s where learning_objects contains %s", odb_class, learning_object.id)
+      build_objects connection.query(query)
     end
 
     def bookmarks(user)