Permalink
Browse files

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
  • Loading branch information...
1 parent e425493 commit 722e0b6a8bb62226437e466b5a98356d026b05f5 @jeremy jeremy committed Jun 20, 2006
View
@@ -1,6 +1,6 @@
*SVN*
-* Row locking. Provide a locking clause with the :lock finder option or true for the default "FOR UPDATE". [Shugo Maeda]
+* Row locking. Provide a locking clause with the :lock finder option or true for the default "FOR UPDATE". Use the #lock method to obtain a row lock on a single reload (reloads the record with :lock => true). [Shugo Maeda]
# Obtain an exclusive lock on person 1 so we can safely increment visits.
Person.transaction do
# select * from people where id=1 for update
@@ -46,7 +46,8 @@
require 'active_record/acts/list'
require 'active_record/acts/tree'
require 'active_record/acts/nested_set'
-require 'active_record/locking'
+require 'active_record/locking/optimistic'
+require 'active_record/locking/pessimistic'
require 'active_record/migration'
require 'active_record/schema'
require 'active_record/calculations'
@@ -55,6 +56,7 @@
ActiveRecord::Base.class_eval do
include ActiveRecord::Validations
include ActiveRecord::Locking::Optimistic
+ include ActiveRecord::Locking::Pessimistic
include ActiveRecord::Callbacks
include ActiveRecord::Observing
include ActiveRecord::Timestamp
@@ -1541,10 +1541,13 @@ def toggle!(attribute)
end
# Reloads the attributes of this object from the database.
- def reload
+ # The optional options argument is passed to find when reloading so you
+ # may do e.g. record.reload(:lock => true) to reload the same record with
+ # an exclusive row lock.
+ def reload(options = nil)
clear_aggregation_cache
clear_association_cache
- @attributes.update(self.class.find(self.id).instance_variable_get('@attributes'))
+ @attributes.update(self.class.find(self.id, options).instance_variable_get('@attributes'))
self
end
@@ -49,8 +49,8 @@ def update_with_lock #:nodoc:
affected_rows = connection.update(<<-end_sql, "#{self.class.name} Update with optimistic locking")
UPDATE #{self.class.table_name}
SET #{quoted_comma_pair_list(connection, attributes_with_quotes(false))}
- WHERE #{self.class.primary_key} = #{quote(id)}
- AND #{lock_col} = #{quote(previous_value)}
+ WHERE #{self.class.primary_key} = #{quote(id)}
+ AND #{self.class.quoted_locking_column} = #{quote(previous_value)}
end_sql
unless affected_rows == 1
@@ -74,6 +74,11 @@ def locking_column
reset_locking_column
end
+ # Quote the column name used for optimistic locking.
+ def quoted_locking_column
+ connection.quote_column_name(locking_column)
+ end
+
# Reset the column used for optimistic locking back to the lock_version default.
def reset_locking_column
set_locking_column DEFAULT_LOCKING_COLUMN
@@ -0,0 +1,77 @@
+# 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
@@ -82,6 +82,18 @@ def test_sane_find_with_lock
end
end
+ # Locking a record reloads it.
+ def test_sane_lock_method
+ assert_nothing_raised do
+ Person.transaction do
+ person = Person.find 1
+ old, person.first_name = person.first_name, 'fooman'
+ person.lock!
+ assert_equal old, person.first_name
+ end
+ end
+ end
+
if current_adapter?(:PostgreSQLAdapter)
def test_no_locks_no_wait
first, second = duel { Person.find 1 }

0 comments on commit 722e0b6

Please sign in to comment.