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