Module: ActiveRecord::Locking::Optimistic
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Extension / Inclusion / Inheritance Descendants | |
Included In:
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Class Chain:
self,
::ActiveSupport::Concern
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Defined in: | activerecord/lib/active_record/locking/optimistic.rb |
Overview
What is Optimistic Locking
Optimistic
locking allows multiple users to access the same record for edits, and assumes a minimum of conflicts with the data. It does this by checking whether another process has made changes to a record since it was opened, an ::ActiveRecord::StaleObjectError
exception is thrown if that has occurred and the update is ignored.
Check out Pessimistic
for an alternative.
Usage
Active Record supports optimistic locking if the lock_version
field is present. Each update to the record increments the integer column lock_version
and the locking facilities ensure that records instantiated twice will let the last one saved raise a ::ActiveRecord::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 an ActiveRecord::StaleObjectError
Optimistic
locking will also check for stale data when objects are destroyed. Example:
p1 = Person.find(1)
p2 = Person.find(1)
p1.first_name = "Michael"
p1.save
p2.destroy # Raises an 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.
This locking mechanism will function inside a single Ruby process. To make it work across all web requests, the recommended approach is to add lock_version
as a hidden field to your form.
This behavior can be turned off by setting ActiveRecord::Base.lock_optimistically = false
. To override the name of the lock_version
column, set the locking_column
class attribute:
class Person < ActiveRecord::Base
self.locking_column = :lock_person
end
Class Method Summary
::ActiveSupport::Concern
- Extended
class_methods | Define class methods from given block. |
included | Evaluate given block in context of base class, so that you can write class macros here. |
prepended | Evaluate given block in context of base class, so that you can write class macros here. |
DSL Calls
included
[ GitHub ]55 56 57
# File 'activerecord/lib/active_record/locking/optimistic.rb', line 55
included do class_attribute :lock_optimistically, instance_writer: false, default: true end