class AddHeadPipelineForEachMergeRequest < ActiveRecord::Migration
  include Gitlab::Database::MigrationHelpers

  DOWNTIME = false

  def up
    disable_statement_timeout

    pipelines = Arel::Table.new(:ci_pipelines)
    merge_requests = Arel::Table.new(:merge_requests)

    head_id = pipelines.
      project(Arel::Nodes::NamedFunction.new('max', [pipelines[:id]])).
      from(pipelines).
      where(pipelines[:ref].eq(merge_requests[:source_branch])).
      where(pipelines[:project_id].eq(merge_requests[:source_project_id]))

    sub_query = Arel::Nodes::SqlLiteral.new(Arel::Nodes::Grouping.new(head_id).to_sql)

    update_column_in_batches(:merge_requests, :head_pipeline_id, sub_query)
  end

  def down
  end
end