Add foreign key on pipeline_schedules.owner_id

Set to nullify, so the settings remain if the user is deleted.

Fixes gitlab-org/gitlab-ce#31932

db/post_migrate/20170510101043_add_foreign_key_on_pipeline_schedule_owner.rb

+class AddForeignKeyOnPipelineScheduleOwner < ActiveRecord::Migration
+  include Gitlab::Database::MigrationHelpers
+
+  DOWNTIME = false
+
+  disable_ddl_transaction!
+
+  def up
+    execute <<-SQL
+      UPDATE ci_pipeline_schedules
+      SET owner_id = NULL
+      WHERE NOT EXISTS (
+        SELECT true
+        FROM users
+        WHERE ci_pipeline_schedules.owner_id = users.id
+      )
+    SQL
+
+    add_concurrent_foreign_key(:ci_pipeline_schedules, :users, column: :owner_id, on_delete: on_delete)
+  end
+
+  def down
+    remove_foreign_key(:ci_pipeline_schedules, column: :owner_id)
+  end
+
+  private
+
+  def on_delete
+    if Gitlab::Database.mysql?
+      :nullify
+    else
+      'SET NULL'
+    end
+  end
+end

db/schema.rb

@@ -11,7 +11,7 @@
 #
 # It's strongly recommended that you check this file into your version control system.
-ActiveRecord::Schema.define(version: 20170508190732) do
+ActiveRecord::Schema.define(version: 20170510101043) do
   # These are extensions that must be enabled in order to support this database
   enable_extension "plpgsql"
@@ -1413,6 +1413,7 @@ ActiveRecord::Schema.define(version: 20170508190732) do
   add_foreign_key "chat_teams", "namespaces", on_delete: :cascade
   add_foreign_key "ci_builds", "ci_pipelines", column: "auto_canceled_by_id", name: "fk_a2141b1522", on_delete: :nullify
   add_foreign_key "ci_pipeline_schedules", "projects", name: "fk_8ead60fcc4", on_delete: :cascade
+  add_foreign_key "ci_pipeline_schedules", "users", column: "owner_id", name: "fk_9ea99f58d2", on_delete: :nullify
   add_foreign_key "ci_pipelines", "ci_pipeline_schedules", column: "pipeline_schedule_id", name: "fk_3d34ab2e06", on_delete: :nullify
   add_foreign_key "ci_pipelines", "ci_pipelines", column: "auto_canceled_by_id", name: "fk_262d4c2d19", on_delete: :nullify
   add_foreign_key "ci_trigger_requests", "ci_triggers", column: "trigger_id", name: "fk_b8ec8b7245", on_delete: :cascade