NAME

       DBIx::Class::OptimisticLocking - Optimistic locking support for DBIx::Class

VERSION

       version 0.02

SYNOPSIS

       This module allows the user to utilize optimistic locking when updating a row.

       Example usage:

               package DB::Main::Orders;

               use base qw/DBIx::Class/;

               __PACKAGE__->load_components(qw/OptimisticLocking Core/);

               __PACKAGE__->optimistic_locking_strategy('dirty'); # this is the default behavior

PURPOSE

       Optimistic locking is an alternative to using exclusive locks when you have the
       possibility of concurrent, conflicting updates in your database.  The basic principle is
       you allow any and all clients to issue updates and rather than preemptively synchronizing
       all data modifications (which is what happens with exclusive locks) you are "optimistic"
       that updates won't interfere with one another and the updates will only fail when they do
       in fact interfere with one another.

       Consider the following scenario (in timeline order, not in the same block of code):

               my $order = $schema->resultset('Orders')->find(1);

               # some other different, concurrent process loads the same object
               my $other_order = $schema->resultset('Orders')->find(1);

               $order->status('fraud review');
               $other_order->status('processed');

               $order->update; # this succeeds
               $other_order->update; # this fails when using optimistic locking

       Without locking (optimistic or exclusive ), the example order would have two sequential
       updates issued with the second essentially erasing the results of the first.  With
       optimistic locking, the second update (on $other_order) would fail.

       This optimistic locking is typically done by adding additional restrictions to the "WHERE"
       clause of the "UPDATE" statement.  These additional restrictions ensure the data is still
       in the expected state before applying the update.  This DBIx::Class::OptimisticLocking
       component provides a few different strategies for providing this functionality.

CONFIGURATION

   optimistic_locking_strategy
       This configuration controls the main functionality of this component.  The current
       recognized optimistic locking modes supported are:

       •   dirty

           When issuing an update, the "WHERE" clause of the update will include all of the
           original values of the columns that are being updated.  Any columns that are not being
           updated will be ignored.

       •   version

           When issuing an update, the "WHERE" clause of the update will include a check of the
           "version" column (or otherwise configured column using
           optimistic_locking_version_column).  The "version" column will also be incremented on
           each update as well.  The exception is if all of the updated columns are in the
           optimistic_locking_ignore_columns configuration.

       •   all

           When issuing an update, the "WHERE" clause of the update will include a check on each
           column in the object regardless of whether they were updated or not.

       •   none (or any other value)

           This turns off the functionality of this component.  But why would you load it if you
           don't need it? :-)

   optimistic_locking_ignore_columns
       Occassionally you may elect to ignore certain columns that are not significant enough to
       detect colisions and cause the update to fail.  For instance, if you have a timestamp
       column, you may want to add that to this list so that it is ignored when generating the
       "UPDATE" where clause for the update.

   optimistic_locking_version_column
       If you are using 'version' as your optimistic_locking_strategy, you can optionally specify
       a different name for the column used for version tracking.  If an alternate name is not
       passed, the component will look for a column named "version" in your model.

EXTENDED METHODS

   update
       See DBIx::Class::Row::update for basic usage.

       Before issuing the actual update, this component injects additional criteria that will be
       used in the "WHERE" clause in the "UPDATE". The criteria that is used depends on the
       CONFIGURATION defined in the model class.

   _track_storage_value
       This is a method internal to DBIx::Class::Row that basically serves as a predicate method
       that indicates whether or not the orginal value of the row (as loaded from storage) should
       be recorded when it is updated.

       Typically, only primary key values are persisted but for DBIx::Class::OptimisticLocking,
       this list is augmented to include other columns based on the optimistic locking strategy
       that is configured for this DBIx::Class::ResultSource.  For instance, if the chosen
       strategy is '"dirty"' (the default), every column's original value will be tracked in
       order to generate the appropriate "WHERE" clause in any subsequent "UPDATE" operations.

   _storage_ident_condition
       This is an internal method to DBIx::Class::PK that generates the "WHERE" clause for update
       and delete operations.

BUGS

       Please report any bugs or feature requests to "bug-dbix-class-optimisticlocking at
       rt.cpan.org", or through the web interface at
       <http://rt.cpan.org/NoAuth/ReportBug.html?Queue=DBIx-Class-OptimisticLocking>.  I will be
       notified, and then you'll automatically be notified of progress on your bug as I make
       changes.

SUPPORT

       You can find documentation for this module with the perldoc command.

           perldoc DBIx::Class::OptimisticLocking

ACKNOWLEDGEMENTS

       Credit goes to the Java ORM package Hibernate <http://hibernate.org> for inspiring me to
       write this for DBIx::Class.

AUTHOR

         Brian Phillips <bphillips@cpan.org>

COPYRIGHT AND LICENSE

       This software is copyright (c) 2011 by Brian Phillips.

       This is free software; you can redistribute it and/or modify it under the same terms as
       the Perl 5 programming language system itself.