class Arel::SelectManager

def lock(locking = Arel.sql("FOR UPDATE"))
  case locking
  when true
    locking = Arel.sql("FOR UPDATE")
  when Arel::Nodes::SqlLiteral
  when String
    locking = Arel.sql locking
  end
  @ast.lock = Nodes::Lock.new(locking)
  self
end