Add foreign key on trigger requests

I started out as I missed the foreign key on ci_triggers and projects.
However, it seemed Yorick caught this already on gitlab-org/gitlab-ce!9388.

Still I found a missing foreign key, between the trigger requests and
triggers. This commit adds it, and removes the depend: :destroy on the
Rails model Ci::Triggers

app/models/ci/trigger.rb

@@ -7,7 +7,7 @@ module Ci
     belongs_to :project
     belongs_to :owner, class_name: "User"
 
-    has_many :trigger_requests, dependent: :destroy
+    has_many :trigger_requests
     has_one :trigger_schedule, dependent: :destroy
 
     validates :token, presence: true, uniqueness: true

changelogs/unreleased/zj-fk-ci-triggers.yml

+---
+title: Add foreign key for ci_trigger_requests on ci_triggers
+merge_request: 10537
+author:

db/migrate/20170407135259_add_foreigh_key_trigger_requests_trigger.rb

+class AddForeighKeyTriggerRequestsTrigger < ActiveRecord::Migration
+  include Gitlab::Database::MigrationHelpers
+
+  DOWNTIME = false
+
+  disable_ddl_transaction!
+
+  def up
+    add_concurrent_foreign_key(:ci_trigger_requests, :ci_triggers, column: :trigger_id)
+  end
+
+  def down
+    remove_foreign_key(:ci_trigger_requests, column: :trigger_id)
+  end
+end

db/schema.rb

@@ -12,6 +12,7 @@
 # It's strongly recommended that you check this file into your version control system.
 
 ActiveRecord::Schema.define(version: 20170408033905) do
+
   # These are extensions that must be enabled in order to support this database
   enable_extension "plpgsql"
   enable_extension "pg_trgm"
@@ -1356,6 +1357,7 @@ ActiveRecord::Schema.define(version: 20170408033905) 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_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
   add_foreign_key "ci_trigger_schedules", "ci_triggers", column: "trigger_id", name: "fk_90a406cc94", on_delete: :cascade
   add_foreign_key "ci_triggers", "users", column: "owner_id", name: "fk_e8e10d1964", on_delete: :cascade
   add_foreign_key "container_repositories", "projects"