global

def load_children(keys, lock: nil)
  scope = child_constraints.inject(child_type.unscoped) do |sc, (col, val)|
    sc.where(col => val)
  end
  if lock
    scope = scope.order(:id).lock(lock)
  end
  scope.where(child_key_column => keys).group_by { |c| c.read_attribute(child_key_column) }
end