From 722e0b6a8bb62226437e466b5a98356d026b05f5 Mon Sep 17 00:00:00 2001 From: Jeremy Kemper Date: Tue, 20 Jun 2006 01:58:36 +0000 Subject: r4664@asus: jeremy | 2006-06-19 18:55:36 -0700 Use the #lock method to obtain a row lock on a single record. Simply reloads the record with :lock => true. git-svn-id: http://svn-commit.rubyonrails.org/rails/trunk@4462 5ecf4fe2-1ee6-0310-87b1-e25e094e27de --- .../lib/active_record/locking/pessimistic.rb | 77 ++++++++++++++++++++++ 1 file changed, 77 insertions(+) create mode 100644 activerecord/lib/active_record/locking/pessimistic.rb (limited to 'activerecord/lib/active_record/locking/pessimistic.rb') diff --git a/activerecord/lib/active_record/locking/pessimistic.rb b/activerecord/lib/active_record/locking/pessimistic.rb new file mode 100644 index 0000000000..caad760742 --- /dev/null +++ b/activerecord/lib/active_record/locking/pessimistic.rb @@ -0,0 +1,77 @@ +# Copyright (c) 2006 Shugo Maeda +# +# 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 -- cgit v1.2.3