Add database foreign key between pipelines and builds

db/migrate/20180420010016_add_pipeline_build_foreign_key.rb

+class AddPipelineBuildForeignKey < ActiveRecord::Migration
+  include Gitlab::Database::MigrationHelpers
+
+  DOWNTIME = false
+
+  disable_ddl_transaction!
+
+  def up
+    execute <<~SQL
+      DELETE FROM ci_builds WHERE NOT EXISTS
+        (SELECT true FROM ci_pipelines WHERE ci_pipelines.id = ci_builds.commit_id)
+    SQL
+
+    return if foreign_key_exists?(:ci_builds, :ci_pipelines, column: :commit_id)
+
+    add_concurrent_foreign_key(:ci_builds, :ci_pipelines, column: :commit_id)
+  end
+
+  def down
+    return unless foreign_key_exists?(:ci_builds, :ci_pipelines, column: :commit_id)
+
+    remove_foreign_key(:ci_builds, column: :commit_id)
+  end
+end

spec/migrations/add_pipeline_build_foreign_key_spec.rb

+require 'spec_helper'
+require Rails.root.join('db', 'migrate', '20180420010016_add_pipeline_build_foreign_key.rb')
+
+describe AddPipelineBuildForeignKey, :migration do
+  let(:namespaces) { table(:namespaces) }
+  let(:projects) { table(:projects) }
+  let(:pipelines) { table(:ci_pipelines) }
+  let(:builds) { table(:ci_builds) }
+
+  before do
+    namespaces.create(id: 10, name: 'gitlab-org', path: 'gitlab-org')
+    projects.create!(id: 11, namespace_id: 10, name: 'gitlab', path: 'gitlab')
+    pipelines.create!(id: 12, project_id: 11, ref: 'master', sha: 'adf43c3a')
+
+    builds.create!(id: 101, commit_id: 12, project_id: 11)
+    builds.create!(id: 102, commit_id: 222, project_id: 11)
+    builds.create!(id: 103, commit_id: 333, project_id: 11)
+    builds.create!(id: 104, commit_id: 12, project_id: 11)
+  end
+
+  it 'adds foreign key after removing orphans' do
+    expect(builds.all.count).to eq 4
+    expect(foreign_key_exists?(:ci_builds, :ci_pipelines, column: :commit_id)).to be_falsey
+
+    migrate!
+
+    expect(builds.all.pluck(:id)).to eq [101, 104]
+    expect(foreign_key_exists?(:ci_builds, :ci_pipelines, column: :commit_id)).to be_truthy
+  end
+end

spec/support/helpers/migrations_helpers.rb

@@ -24,6 +24,17 @@ module MigrationsHelpers
     end
   end
 
+  def foreign_key_exists?(source, target = nil, column: nil)
+    ActiveRecord::Base.connection.foreign_keys(source).any? do |key|
+      if column
+        key.options[:column].to_s == column.to_s
+      else
+        key.to_table.to_s == target.to_s
+      end
+    end
+  end
+
+
   def reset_column_in_all_models
     clear_schema_cache!