Add order_by updated_at to Pipelines API

This allows order_by updated_at on the Pipelines API so users can query
for the most recent updates. It adds a database index to ensure the
feature is performant.

app/finders/pipelines_finder.rb

@@ -3,7 +3,7 @@
 class PipelinesFinder
   attr_reader :project, :pipelines, :params, :current_user
 
-  ALLOWED_INDEXED_COLUMNS = %w[id status ref user_id].freeze
+  ALLOWED_INDEXED_COLUMNS = %w[id status ref updated_at user_id].freeze
 
   def initialize(project, current_user, params = {})
     @project = project

changelogs/unreleased/33099-add-pipelines-api-order-by-updated-at.yml

+---
+title: Allow order_by updated_at in Pipelines API
+merge_request: 19886
+author:
+type: added

db/migrate/20191111175230_add_index_on_ci_pipelines_updated_at.rb

+# frozen_string_literal: true
+
+class AddIndexOnCiPipelinesUpdatedAt < ActiveRecord::Migration[5.2]
+  include Gitlab::Database::MigrationHelpers
+
+  DOWNTIME = false
+  INDEX_COLUMNS = [:project_id, :status, :updated_at]
+
+  disable_ddl_transaction!
+
+  def up
+    add_concurrent_index(:ci_pipelines, INDEX_COLUMNS)
+  end
+
+  def down
+    remove_concurrent_index(:ci_pipelines, INDEX_COLUMNS)
+  end
+end

db/schema.rb

@@ -846,6 +846,7 @@ ActiveRecord::Schema.define(version: 2019_11_12_115317) do
     t.index ["project_id", "sha"], name: "index_ci_pipelines_on_project_id_and_sha"
     t.index ["project_id", "source"], name: "index_ci_pipelines_on_project_id_and_source"
     t.index ["project_id", "status", "config_source"], name: "index_ci_pipelines_on_project_id_and_status_and_config_source"
+    t.index ["project_id", "status", "updated_at"], name: "index_ci_pipelines_on_project_id_and_status_and_updated_at"
     t.index ["project_id"], name: "index_ci_pipelines_on_project_id"
     t.index ["status"], name: "index_ci_pipelines_on_status"
     t.index ["user_id"], name: "index_ci_pipelines_on_user_id"

doc/api/pipelines.md

@@ -18,7 +18,7 @@ GET /projects/:id/pipelines
 | `yaml_errors`| boolean  | no       | Returns pipelines with invalid configurations |
 | `name`| string  | no       | The name of the user who triggered pipelines |
 | `username`| string  | no       | The username of the user who triggered pipelines |
-| `order_by`| string  | no       | Order pipelines by `id`, `status`, `ref`, or `user_id` (default: `id`) |
+| `order_by`| string  | no       | Order pipelines by `id`, `status`, `ref`, `updated_at` or `user_id` (default: `id`) |
 | `sort`    | string  | no       | Sort pipelines in `asc` or `desc` order (default: `desc`) |
 
 ```