add pipeline id to merge request metrics table. Also, updated the pipeline worker to populate this field.

app/models/merge_request.rb

@@ -232,7 +232,7 @@ class MergeRequest < ActiveRecord::Base
   end
 
   def diff_head_commit
-    if persisted?
+    if persisted?diff_head_commit
       merge_request_diff.head_commit
     else
       source_branch_head

app/models/merge_request/metrics.rb

@@ -1,5 +1,6 @@
 class MergeRequest::Metrics < ActiveRecord::Base
   belongs_to :merge_request
+  belongs_to :pipeline, class_name: 'Ci::Pipeline', foreign_key: :ci_commit_id
 
   def record!
     if merge_request.merged? && self.merged_at.blank?

app/workers/pipeline_metrics_worker.rb

@@ -12,11 +12,11 @@ class PipelineMetricsWorker
   private
 
   def update_metrics_for_active_pipeline(pipeline)
-    metrics(pipeline).update_all(latest_build_started_at: pipeline.started_at, latest_build_finished_at: nil)
+    metrics(pipeline).update_all(latest_build_started_at: pipeline.started_at, latest_build_finished_at: nil, ci_commit_id: pipeline.id)
   end
 
   def update_metrics_for_succeeded_pipeline(pipeline)
-    metrics(pipeline).update_all(latest_build_started_at: pipeline.started_at, latest_build_finished_at: pipeline.finished_at)
+    metrics(pipeline).update_all(latest_build_started_at: pipeline.started_at, latest_build_finished_at: pipeline.finished_at, ci_commit_id: pipeline.id)
   end
 
   def metrics(pipeline)

db/migrate/20161020083353_add_pipeline_id_to_merge_request_metrics.rb

@@ -0,0 +1,29 @@
+# See http://doc.gitlab.com/ce/development/migration_style_guide.html
+# for more information on how to write migrations for GitLab.
+
+class AddPipelineIdToMergeRequestMetrics < ActiveRecord::Migration
+  include Gitlab::Database::MigrationHelpers
+
+  # Set this constant to true if this migration requires downtime.
+  DOWNTIME = true
+
+  # When a migration requires downtime you **must** uncomment the following
+  # constant and define a short and easy to understand explanation as to why the
+  # migration requires downtime.
+  DOWNTIME_REASON = 'Adding a foreign key'
+
+  # When using the methods "add_concurrent_index" or "add_column_with_default"
+  # you must disable the use of transactions as these methods can not run in an
+  # existing transaction. When using "add_concurrent_index" make sure that this
+  # method is the _only_ method called in the migration, any other changes
+  # should go in a separate migration. This ensures that upon failure _only_ the
+  # index creation fails and can be retried or reverted easily.
+  #
+  # To disable transactions uncomment the following line and remove these
+  # comments:
+  # disable_ddl_transaction!
+
+  def change
+    add_reference :merge_request_metrics, :ci_commit, index: true, foreign_key: { on_delete: :cascade }
+  end
+end

db/schema.rb

@@ -634,8 +634,10 @@ ActiveRecord::Schema.define(version: 20161109150329) do
     t.datetime "merged_at"
     t.datetime "created_at", null: false
     t.datetime "updated_at", null: false
+    t.integer "ci_commit_id"
   end
 
+  add_index "merge_request_metrics", ["ci_commit_id"], name: "index_merge_request_metrics_on_ci_commit_id", using: :btree
   add_index "merge_request_metrics", ["first_deployed_to_production_at"], name: "index_merge_request_metrics_on_first_deployed_to_production_at", using: :btree
   add_index "merge_request_metrics", ["merge_request_id"], name: "index_merge_request_metrics", using: :btree
 
@@ -1244,6 +1246,7 @@ ActiveRecord::Schema.define(version: 20161109150329) do
   add_foreign_key "labels", "namespaces", column: "group_id", on_delete: :cascade
   add_foreign_key "lists", "boards"
   add_foreign_key "lists", "labels"
+  add_foreign_key "merge_request_metrics", "ci_commits", on_delete: :cascade
   add_foreign_key "merge_request_metrics", "merge_requests", on_delete: :cascade
   add_foreign_key "merge_requests_closing_issues", "issues", on_delete: :cascade
   add_foreign_key "merge_requests_closing_issues", "merge_requests", on_delete: :cascade