Add cluster_id to deployments table as an FK

We nullify when cluster is deleted as we want to keep the deployment
record around.

Add cluster as an optional association

We will have only cluster for deployments where the build deploys to a
kubernetes cluster

app/models/deployment.rb

@@ -7,6 +7,7 @@ class Deployment < ApplicationRecord
 
   belongs_to :project, required: true
   belongs_to :environment, required: true
+  belongs_to :cluster, class_name: 'Clusters::Cluster', optional: true
   belongs_to :user
   belongs_to :deployable, polymorphic: true # rubocop:disable Cop/PolymorphicAssociations
 

db/migrate/20190623212503_add_cluster_id_to_deployments.rb

@@ -0,0 +1,9 @@
+# frozen_string_literal: true
+
+class AddClusterIdToDeployments < ActiveRecord::Migration[5.1]
+  DOWNTIME = false
+
+  def change
+    add_column :deployments, :cluster_id, :integer
+  end
+end

db/migrate/20190627051902_add_cluster_id_index_fk_to_deployments.rb

@@ -0,0 +1,21 @@
+# frozen_string_literal: true
+
+class AddClusterIdIndexFkToDeployments < ActiveRecord::Migration[5.1]
+  include Gitlab::Database::MigrationHelpers
+
+  DOWNTIME = false
+
+  disable_ddl_transaction!
+
+  def up
+    add_concurrent_index :deployments, :cluster_id
+
+    add_concurrent_foreign_key :deployments, :clusters, column: :cluster_id, on_delete: :nullify
+  end
+
+  def down
+    remove_foreign_key :deployments, :clusters
+
+    remove_concurrent_index :deployments, :cluster_id
+  end
+end

db/schema.rb

@@ -10,7 +10,7 @@
 #
 # It's strongly recommended that you check this file into your version control system.
 
-ActiveRecord::Schema.define(version: 20190625184066) do
+ActiveRecord::Schema.define(version: 20190627051902) do
 
   # These are extensions that must be enabled in order to support this database
   enable_extension "plpgsql"
@@ -1066,6 +1066,8 @@ ActiveRecord::Schema.define(version: 20190625184066) do
     t.string "on_stop"
     t.integer "status", limit: 2, null: false
     t.datetime_with_timezone "finished_at"
+    t.integer "cluster_id"
+    t.index ["cluster_id"], name: "index_deployments_on_cluster_id", using: :btree
     t.index ["created_at"], name: "index_deployments_on_created_at", using: :btree
     t.index ["deployable_type", "deployable_id"], name: "index_deployments_on_deployable_type_and_deployable_id", using: :btree
     t.index ["environment_id", "id"], name: "index_deployments_on_environment_id_and_id", using: :btree
@@ -3650,6 +3652,7 @@ ActiveRecord::Schema.define(version: 20190625184066) do
   add_foreign_key "dependency_proxy_blobs", "namespaces", column: "group_id", name: "fk_db58bbc5d7", on_delete: :cascade
   add_foreign_key "dependency_proxy_group_settings", "namespaces", column: "group_id", name: "fk_616ddd680a", on_delete: :cascade
   add_foreign_key "deploy_keys_projects", "projects", name: "fk_58a901ca7e", on_delete: :cascade
+  add_foreign_key "deployments", "clusters", name: "fk_289bba3222", on_delete: :nullify
   add_foreign_key "deployments", "projects", name: "fk_b9a3851b82", on_delete: :cascade
   add_foreign_key "design_management_designs", "issues", on_delete: :cascade
   add_foreign_key "design_management_designs", "projects", on_delete: :cascade

spec/models/deployment_spec.rb

@@ -7,6 +7,7 @@ describe Deployment do
 
   it { is_expected.to belong_to(:project).required }
   it { is_expected.to belong_to(:environment).required }
+  it { is_expected.to belong_to(:cluster).class_name('Clusters::Cluster') }
   it { is_expected.to belong_to(:user) }
   it { is_expected.to belong_to(:deployable) }