Pessimistic Locking Strategy support for DataMapper (FOR UPDATE)

gistfile1.rb

# This Patch makes it possible to retrieve row-locked records from data-objects repositories
# Sample Usage: User.locked.get(1)
#               #=> SELECT [...] WHERE `id` = 1 ORDER BY `id` LIMIT 1 FOR UPDATE

# In user.rb
def self.locked
  all(:with_locking => true)
end

# The actual patch
module DataMapper
  # Add Pessimistic Locking
  module Adapters
    class DataObjectsAdapter
      module PessimisticLocking
        def select_statement query
          statement, bind_values = super query
          statement << ' FOR UPDATE' if query.locked?
          return statement, bind_values
        end
      end
      include PessimisticLocking
    end
  end
  class Query
    OPTIONS += [:with_locking]
    OPTIONS.freeze

    def locked?
      @options[:with_locking]
    end

    def assert_valid_options_with_locking options
      assert_valid_options_without_locking options.except(:with_locking)
    end
    alias_method_chain :assert_valid_options, :locking
  end
end

This is awesome! What do you think about packaging this up into a dm-* plugin? I know there's dm-optlock for optimistic locking (and probably a few others), but I'm not aware of any that do pessimistic locking.

This is related https://gist.github.com/323511#comments