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2
6 DBIx::Class::OptimisticLocking - Optimistic locking support for
7 DBIx::Class
8
10 version 0.02
11
13 This module allows the user to utilize optimistic locking when updating
14 a row.
15 Example usage:
17 package DB::Main::Orders;
19 use base qw/DBIx::Class/;
21 __PACKAGE__->load_components(qw/OptimisticLocking Core/);
23 __PACKAGE__->optimistic_locking_strategy('dirty'); # this is the default behavior
25
27 Optimistic locking is an alternative to using exclusive locks when you
28 have the possibility of concurrent, conflicting updates in your
29 database. The basic principle is you allow any and all clients to
30 issue updates and rather than preemptively synchronizing all data
31 modifications (which is what happens with exclusive locks) you are
32 "optimistic" that updates won't interfere with one another and the
33 updates will only fail when they do in fact interfere with one another.
34 Consider the following scenario (in timeline order, not in the same
36 block of code):
37 my $order = $schema->resultset('Orders')->find(1);
39 # some other different, concurrent process loads the same object
41 my $other_order = $schema->resultset('Orders')->find(1);
42 $order->status('fraud review');
44 $other_order->status('processed');
45 $order->update; # this succeeds
47 $other_order->update; # this fails when using optimistic locking
48 Without locking (optimistic or exclusive ), the example order would
50 have two sequential updates issued with the second essentially erasing
51 the results of the first. With optimistic locking, the second update
52 (on $other_order) would fail.
53 This optimistic locking is typically done by adding additional
55 restrictions to the "WHERE" clause of the "UPDATE" statement. These
56 additional restrictions ensure the data is still in the expected state
57 before applying the update. This DBIx::Class::OptimisticLocking
58 component provides a few different strategies for providing this
59 functionality.
60
62 optimistic_locking_strategy
63 This configuration controls the main functionality of this component.
64 The current recognized optimistic locking modes supported are:
65 · dirty
67 When issuing an update, the "WHERE" clause of the update will
69 include all of the original values of the columns that are being
70 updated. Any columns that are not being updated will be ignored.
71 · version
73 When issuing an update, the "WHERE" clause of the update will
75 include a check of the "version" column (or otherwise configured
76 column using optimistic_locking_version_column). The "version"
77 column will also be incremented on each update as well. The
78 exception is if all of the updated columns are in the
79 optimistic_locking_ignore_columns configuration.
80 · all
82 When issuing an update, the "WHERE" clause of the update will
84 include a check on each column in the object regardless of whether
85 they were updated or not.
86 · none (or any other value)
88 This turns off the functionality of this component. But why would
90 you load it if you don't need it? :-)
91 optimistic_locking_ignore_columns
93 Occassionally you may elect to ignore certain columns that are not
94 significant enough to detect colisions and cause the update to fail.
95 For instance, if you have a timestamp column, you may want to add that
96 to this list so that it is ignored when generating the "UPDATE" where
97 clause for the update.
98 optimistic_locking_version_column
100 If you are using 'version' as your optimistic_locking_strategy, you can
101 optionally specify a different name for the column used for version
102 tracking. If an alternate name is not passed, the component will look
103 for a column named "version" in your model.
104
106 update
107 See DBIx::Class::Row::update for basic usage.
108 Before issuing the actual update, this component injects additional
110 criteria that will be used in the "WHERE" clause in the "UPDATE". The
111 criteria that is used depends on the CONFIGURATION defined in the model
112 class.
113 _track_storage_value
115 This is a method internal to DBIx::Class::Row that basically serves as
116 a predicate method that indicates whether or not the orginal value of
117 the row (as loaded from storage) should be recorded when it is updated.
118 Typically, only primary key values are persisted but for
120 DBIx::Class::OptimisticLocking, this list is augmented to include other
121 columns based on the optimistic locking strategy that is configured for
122 this DBIx::Class::ResultSource. For instance, if the chosen strategy
123 is '"dirty"' (the default), every column's original value will be
124 tracked in order to generate the appropriate "WHERE" clause in any
125 subsequent "UPDATE" operations.
126 _storage_ident_condition
128 This is an internal method to DBIx::Class::PK that generates the
129 "WHERE" clause for update and delete operations.
130
132 Please report any bugs or feature requests to
133 "bug-dbix-class-optimisticlocking at rt.cpan.org", or through the web
134 interface at
135 <http://rt.cpan.org/NoAuth/ReportBug.html?Queue=DBIx-Class-OptimisticLocking>.
136 I will be notified, and then you'll automatically be notified of
137 progress on your bug as I make changes.
138
140 You can find documentation for this module with the perldoc command.
141 perldoc DBIx::Class::OptimisticLocking
143
145 Credit goes to the Java ORM package Hibernate <http://hibernate.org>
146 for inspiring me to write this for DBIx::Class.
147
149 Brian Phillips <bphillips@cpan.org>
150
152 This software is copyright (c) 2011 by Brian Phillips.
153 This is free software; you can redistribute it and/or modify it under
155 the same terms as the Perl 5 programming language system itself.
156perl v5.28.0 2011-08-22 DBIx::Class::OptimisticLocking(3)