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r4663@asus: jeremy | 2006-06-19 17:23:57 -0700
ActiveRecord::Locking is now ActiveRecord::Locking::Optimistic (to make way for Pessimistic.) git-svn-id: http://svn-commit.rubyonrails.org/rails/trunk@4461 5ecf4fe2-1ee6-0310-87b1-e25e094e27de
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Original file line number | Diff line number | Diff line change |
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@@ -1,77 +1,84 @@ | ||
module ActiveRecord | ||
# Active Records support optimistic locking if the field <tt>lock_version</tt> is present. Each update to the | ||
# record increments the lock_version column and the locking facilities ensure that records instantiated twice | ||
# will let the last one saved raise a StaleObjectError if the first was also updated. Example: | ||
# | ||
# p1 = Person.find(1) | ||
# p2 = Person.find(1) | ||
# | ||
# p1.first_name = "Michael" | ||
# p1.save | ||
# | ||
# p2.first_name = "should fail" | ||
# p2.save # Raises a ActiveRecord::StaleObjectError | ||
# | ||
# You're then responsible for dealing with the conflict by rescuing the exception and either rolling back, merging, | ||
# or otherwise apply the business logic needed to resolve the conflict. | ||
# | ||
# You must ensure that your database schema defaults the lock_version column to 0. | ||
# | ||
# This behavior can be turned off by setting <tt>ActiveRecord::Base.lock_optimistically = false</tt>. | ||
# To override the name of the lock_version column, invoke the <tt>set_locking_column</tt> method. | ||
# This method uses the same syntax as <tt>set_table_name</tt> | ||
module Locking | ||
def self.included(base) #:nodoc: | ||
base.class_eval do | ||
alias_method_chain :update, :lock | ||
# Active Records support optimistic locking if the field <tt>lock_version</tt> is present. Each update to the | ||
# record increments the lock_version column and the locking facilities ensure that records instantiated twice | ||
# will let the last one saved raise a StaleObjectError if the first was also updated. Example: | ||
# | ||
# p1 = Person.find(1) | ||
# p2 = Person.find(1) | ||
# | ||
# p1.first_name = "Michael" | ||
# p1.save | ||
# | ||
# p2.first_name = "should fail" | ||
# p2.save # Raises a ActiveRecord::StaleObjectError | ||
# | ||
# You're then responsible for dealing with the conflict by rescuing the exception and either rolling back, merging, | ||
# or otherwise apply the business logic needed to resolve the conflict. | ||
# | ||
# You must ensure that your database schema defaults the lock_version column to 0. | ||
# | ||
# This behavior can be turned off by setting <tt>ActiveRecord::Base.lock_optimistically = false</tt>. | ||
# To override the name of the lock_version column, invoke the <tt>set_locking_column</tt> method. | ||
# This method uses the same syntax as <tt>set_table_name</tt> | ||
module Optimistic | ||
def self.included(base) #:nodoc: | ||
super | ||
base.extend ClassMethods | ||
|
||
base.cattr_accessor :lock_optimistically | ||
base.lock_optimistically = true | ||
|
||
base.alias_method_chain :update, :lock | ||
class << base | ||
alias_method :locking_column=, :set_locking_column | ||
end | ||
end | ||
end | ||
|
||
def update_with_lock #:nodoc: | ||
return update_without_lock unless locking_enabled? | ||
def locking_enabled? #:nodoc: | ||
lock_optimistically && respond_to?(self.class.locking_column) | ||
end | ||
|
||
def update_with_lock #:nodoc: | ||
return update_without_lock unless locking_enabled? | ||
|
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lock_col = self.class.locking_column | ||
previous_value = send(lock_col) | ||
send(lock_col + '=', previous_value + 1) | ||
|
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lock_col = self.class.locking_column | ||
previous_value = send(lock_col) | ||
send(lock_col + '=', previous_value + 1) | ||
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)} | ||
end_sql | ||
|
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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)} | ||
end_sql | ||
unless affected_rows == 1 | ||
raise ActiveRecord::StaleObjectError, "Attempted to update a stale object" | ||
end | ||
|
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unless affected_rows == 1 | ||
raise ActiveRecord::StaleObjectError, "Attempted to update a stale object" | ||
return true | ||
end | ||
|
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return true | ||
end | ||
end | ||
module ClassMethods | ||
DEFAULT_LOCKING_COLUMN = 'lock_version' | ||
|
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class Base | ||
@@lock_optimistically = true | ||
cattr_accessor :lock_optimistically | ||
# Set the column to use for optimistic locking. Defaults to lock_version. | ||
def set_locking_column(value = nil, &block) | ||
define_attr_method :locking_column, value, &block | ||
value | ||
end | ||
|
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def locking_enabled? #:nodoc: | ||
lock_optimistically && respond_to?(self.class.locking_column) | ||
end | ||
|
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class << self | ||
def set_locking_column(value = nil, &block) | ||
define_attr_method :locking_column, value, &block | ||
end | ||
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def locking_column #:nodoc: | ||
reset_locking_column | ||
end | ||
|
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def reset_locking_column #:nodoc: | ||
default = 'lock_version' | ||
set_locking_column(default) | ||
default | ||
# The version column used for optimistic locking. Defaults to lock_version. | ||
def locking_column | ||
reset_locking_column | ||
end | ||
|
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# Reset the column used for optimistic locking back to the lock_version default. | ||
def reset_locking_column | ||
set_locking_column DEFAULT_LOCKING_COLUMN | ||
end | ||
end | ||
end | ||
|
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end | ||
end |