Add explicit primary key for ci_builds_metadata table

app/models/ci/build_metadata.rb

@@ -11,6 +11,7 @@ module Ci
     belongs_to :build, class_name: 'Ci::Build'
     belongs_to :project
 
+    validates :build, presence: true
     validates :project, presence: true
 
     chronic_duration_attr_reader :timeout_human_readable, :timeout

db/migrate/20180301010859_create_ci_builds_metadata_table.rb

@@ -4,16 +4,16 @@ class CreateCiBuildsMetadataTable < ActiveRecord::Migration
   DOWNTIME = false
 
   def change
-    create_table :ci_builds_metadata, id: false do |t|
+    create_table :ci_builds_metadata do |t|
       t.integer :build_id, null: false
       t.integer :project_id, null: false
       t.integer :timeout
       t.integer :timeout_source, null: false, default: 1
 
-      t.primary_key :build_id
       t.foreign_key :ci_builds, column: :build_id, on_delete: :cascade
       t.foreign_key :projects, column: :project_id, on_delete: :cascade
 
+      t.index :build_id, unique: true
       t.index :project_id
     end
   end

db/schema.rb

@@ -329,12 +329,14 @@ ActiveRecord::Schema.define(version: 20180327101207) do
   add_index "ci_builds", ["updated_at"], name: "index_ci_builds_on_updated_at", using: :btree
   add_index "ci_builds", ["user_id"], name: "index_ci_builds_on_user_id", using: :btree
 
-  create_table "ci_builds_metadata", primary_key: "build_id", force: :cascade do |t|
+  create_table "ci_builds_metadata", force: :cascade do |t|
+    t.integer "build_id", null: false
     t.integer "project_id", null: false
     t.integer "timeout"
     t.integer "timeout_source", default: 1, null: false
   end
 
+  add_index "ci_builds_metadata", ["build_id"], name: "index_ci_builds_metadata_on_build_id", unique: true, using: :btree
   add_index "ci_builds_metadata", ["project_id"], name: "index_ci_builds_metadata_on_project_id", using: :btree
 
   create_table "ci_group_variables", force: :cascade do |t|