Refactor MR code reload

Signed-off-by: NDmitriy Zaporozhets <dmitriy.zaporozhets@gmail.com>

app/controllers/projects/merge_requests_controller.rb

@@ -106,9 +106,6 @@ class Projects::MergeRequestsController < Projects::ApplicationController
     params[:merge_request].delete(:target_project_id)
 
     if @merge_request.update_attributes(params[:merge_request].merge(author_id_of_changes: current_user.id))
-      @merge_request.reload_code
-      @merge_request.mark_as_unchecked
-
       @merge_request.reset_events_cache
 
       respond_to do |format|

app/models/merge_request.rb

@@ -32,7 +32,9 @@ class MergeRequest < ActiveRecord::Base
   belongs_to :source_project, foreign_key: :source_project_id, class_name: "Project"
 
   has_one :merge_request_diff, dependent: :destroy
+
   after_create :create_merge_request_diff
+  after_update :update_merge_request_diff
 
   delegate :commits, :diffs, :last_commit, :last_commit_short_sha, to: :merge_request_diff, prefix: nil
 
@@ -125,6 +127,13 @@ class MergeRequest < ActiveRecord::Base
     end
   end
 
+  def update_merge_request_diff
+    if source_branch_changed? || target_branch_changed?
+      reload_code
+      mark_as_unchecked
+    end
+  end
+
   def reload_code
     if merge_request_diff && opened?
       merge_request_diff.reload_content

lib/api/merge_requests.rb

@@ -116,8 +116,6 @@ module API
           authorize! :modify_merge_request, merge_request
 
           if merge_request.update_attributes attrs
-            merge_request.reload_code
-            merge_request.mark_as_unchecked
             present merge_request, with: Entities::MergeRequest
           else
             handle_merge_request_errors! merge_request.errors