78 lines
3.3 KiB
Ruby
78 lines
3.3 KiB
Ruby
|
# 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 :lock => true 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 :lock => 'some locking clause' 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
|