-# Copyright (c) 2006 Shugo Maeda <shugo@ruby-lang.org>
-#
-# Permission is hereby granted, free of charge, to any person obtaining
-# a copy of this software and associated documentation files (the
-# "Software"), to deal in the Software without restriction, including
-# without limitation the rights to use, copy, modify, merge, publish,
-# distribute, sublicense, and/or sell copies of the Software, and to
-# permit persons to whom the Software is furnished to do so, subject
-# to the following conditions:
-#
-# The above copyright notice and this permission notice shall be
-# included in all copies or substantial portions of the Software.
-#
-# THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
-# EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
-# MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.
-# IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR
-# ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF
-# CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION
-# WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
-
-
-module ActiveRecord
- module Locking
- # Locking::Pessimistic provides support for row-level locking using
- # SELECT ... FOR UPDATE and other lock types.
- #
- # Pass <tt>:lock => true</tt> to ActiveRecord::Base.find to obtain an exclusive
- # lock on the selected rows:
- # # select * from accounts where id=1 for update
- # Account.find(1, :lock => true)
- #
- # Pass <tt>:lock => 'some locking clause'</tt> to give a database-specific locking clause
- # of your own such as 'LOCK IN SHARE MODE' or 'FOR UPDATE NOWAIT'.
- #
- # Example:
- # Account.transaction do
- # # select * from accounts where name = 'shugo' limit 1 for update
- # shugo = Account.find(:first, :conditions => "name = 'shugo'", :lock => true)
- # yuko = Account.find(:first, :conditions => "name = 'yuko'", :lock => true)
- # shugo.balance -= 100
- # shugo.save!
- # yuko.balance += 100
- # yuko.save!
- # end
- #
- # You can also use ActiveRecord::Base#lock! method to lock one record by id.
- # This may be better if you don't need to lock every row. Example:
- # Account.transaction do
- # # select * from accounts where ...
- # accounts = Account.find(:all, :conditions => ...)
- # account1 = accounts.detect { |account| ... }
- # account2 = accounts.detect { |account| ... }
- # # select * from accounts where id=? for update
- # account1.lock!
- # account2.lock!
- # account1.balance -= 100
- # account1.save!
- # account2.balance += 100
- # account2.save!
- # end
- #
- # Database-specific information on row locking:
- # MySQL: http://dev.mysql.com/doc/refman/5.1/en/innodb-locking-reads.html
- # PostgreSQL: http://www.postgresql.org/docs/8.1/interactive/sql-select.html#SQL-FOR-UPDATE-SHARE
- module Pessimistic
- # Obtain a row lock on this record. Reloads the record to obtain the requested
- # lock. Pass an SQL locking clause to append the end of the SELECT statement
- # or pass true for "FOR UPDATE" (the default, an exclusive row lock). Returns
- # the locked record.
- def lock!(lock = true)
- reload(:lock => lock) unless new_record?
- self
- end
- end
- end
-end