adding review concern

app/controllers/concerns/reviewable_controller.rb

+## This concern has all default resource methods for CRUD operations
+## When you use it, be sure that +reviewable+ method is implemented in your controller, otherwise an fatal error will raise.
+module ReviewableController
+  extend ActiveSupport::Concern
+
+  included do
+    before_action :set_review, only: [:show, :destroy, :rate]
+    before_action :authenticate_user!, only: [:create, :rate, :destroy]
+  end
+
+  # GET /v1/collections/1/reviews
+  def index
+    render json: Review.where(reviewable: reviewable)
+  end
+
+  # GET /v1/collections/1/reviews/1
+  def show
+    render json: @review
+  end
+
+  # POST /v1/learning_objects/1/reviews
+  # POST /v1/learning_objects/1/reviews.json
+  def create
+    review = reviewable.reviews.new(review_params.merge(user: current_user))
+
+    if review.save
+      render json: review, status: :created
+    else
+      render json: review.errors, status: :unprocessable_entity
+    end
+  end
+
+  # DELETE /v1/learning_objects/1/reviews/2
+  # DELETE /v1/learning_objects/1/reviews/2.json
+  def destroy
+    @review.destroy
+    render nothing: true, status: :ok
+  end
+
+  # User can rate the review to approve or not
+  # POST /v1/learning_objects/1/reviews/2/rate
+  # POST /v1/learning_objects/1/reviews/2/rate.json
+  def rate
+    approves = params[:approves].to_bool
+    rate = Rate.where(user: current_user, review: @review).first_or_initialize
+
+    if rate.update(approves: approves)
+      render json: rate, status: :ok
+    else
+      render json: rate.errors, status: :unprocessable_entity
+    end
+  end
+
+  protected
+
+  def reviewable
+    resource, id = request.path.split('/')[2, 3]
+    reviewable_model = resource.singularize.classify.constantize
+    @reviewable = reviewable_model.find(id)
+  end
+
+  # Never trust parameters from the scary internet, only allow the white list through.
+  def review_params
+    params.require(:review).permit(:name, :description, :pros, :cons)
+  end
+
+  def set_review
+    @review ||= Review.find(params[:id])
+  end
+
+end
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