Preloads head pipeline for each merge request

app/controllers/concerns/issuable_collections.rb

@@ -47,7 +47,7 @@ module IssuableCollections
   end
   def merge_requests_collection
-    merge_requests_finder.execute.preload(:source_project, :target_project, :author, :assignee, :labels, :milestone, :merge_request_diff, target_project: :namespace)
+    merge_requests_finder.execute.preload(:source_project, :target_project, :author, :assignee, :labels, :milestone, :merge_request_diff, :head_pipeline, target_project: :namespace)
   end
   def issues_finder

app/models/merge_request.rb

@@ -13,6 +13,8 @@ class MergeRequest < ActiveRecord::Base
   has_one :merge_request_diff,
     -> { order('merge_request_diffs.id DESC') }
+  belongs_to :head_pipeline, foreign_key: "head_pipeline_id", class_name: "Ci::Pipeline"
+
   has_many :events, as: :target, dependent: :destroy
   has_many :merge_requests_closing_issues, class_name: 'MergeRequestsClosingIssues', dependent: :delete_all
@@ -829,12 +831,6 @@ class MergeRequest < ActiveRecord::Base
     diverged_commits_count > 0
   end
-  def head_pipeline
-    return unless diff_head_sha && source_project
-
-    @head_pipeline ||= source_project.pipeline_for(source_branch, diff_head_sha)
-  end
-
   def all_pipelines
     return Ci::Pipeline.none unless source_project

app/services/ci/create_pipeline_service.rb

@@ -47,7 +47,7 @@ module Ci
       end
       Ci::Pipeline.transaction do
-        pipeline.save
+        update_merge_requests_head_pipeline if pipeline.save
         Ci::CreatePipelineBuildsService
           .new(project, current_user)
@@ -118,6 +118,12 @@ module Ci
       origin_sha && origin_sha != Gitlab::Git::BLANK_SHA
     end
+    def update_merge_requests_head_pipeline
+      merge_requests = MergeRequest.where(source_branch: @pipeline.ref, source_project: @pipeline.project)
+
+      merge_requests.update_all(head_pipeline_id: @pipeline.id) if merge_requests.any?
+    end
+
     def error(message, save: false)
       pipeline.errors.add(:base, message)
       pipeline.drop if save

changelogs/unreleased/issue_27168_2.yml

+---
+title: Preloads head pipeline for each merge request
+merge_request:
+author:

db/migrate/20170427205316_add_head_pipeline_id_to_merge_requests.rb

+class AddHeadPipelineIdToMergeRequests < ActiveRecord::Migration
+  DOWNTIME = false
+
+  def change
+    add_column :merge_requests, :head_pipeline_id, :integer
+  end
+end

db/schema.rb

@@ -123,6 +123,7 @@ ActiveRecord::Schema.define(version: 20170506185517) do
     t.integer "cached_markdown_version"
     t.boolean "clientside_sentry_enabled", default: false, null: false
     t.string "clientside_sentry_dsn"
+    t.string "default_artifacts_expire_in", default: "0", null: false
   end
   create_table "audit_events", force: :cascade do |t|
@@ -690,6 +691,7 @@ ActiveRecord::Schema.define(version: 20170506185517) do
     t.integer "cached_markdown_version"
     t.datetime "last_edited_at"
     t.integer "last_edited_by_id"
+    t.integer "head_pipeline_id"
   end
   add_index "merge_requests", ["assignee_id"], name: "index_merge_requests_on_assignee_id", using: :btree

spec/lib/gitlab/import_export/safe_model_attributes.yml

@@ -158,6 +158,7 @@ MergeRequest:
 - time_estimate
 - last_edited_at
 - last_edited_by_id
+- head_pipeline_id
 MergeRequestDiff:
 - id
 - state

spec/services/ci/create_pipeline_service_spec.rb

@@ -34,6 +34,18 @@ describe Ci::CreatePipelineService, services: true do
       it { expect(pipeline).to have_attributes(status: 'pending') }
       it { expect(pipeline.builds.first).to be_kind_of(Ci::Build) }
+      it 'updates head pipeline of each merge request' do
+        merge_request_1 = create(:merge_request, source_branch: 'master', target_branch: "branch_1", source_project: project)
+        merge_request_2 = create(:merge_request, source_branch: 'master', target_branch: "branch_2", source_project: project)
+        merge_request_3 = create(:merge_request, source_branch: 'other_branch', target_branch: "branch_2", source_project: project)
+
+        head_pipeline = pipeline
+
+        expect(merge_request_1.reload.head_pipeline).to eq(head_pipeline)
+        expect(merge_request_2.reload.head_pipeline).to eq(head_pipeline)
+        expect(merge_request_3.reload.head_pipeline).to be_nil
+      end
+
       context 'auto-cancel enabled' do
         before do
           project.update(auto_cancel_pending_pipelines: 'enabled')