NAME

Rose::DB::Object::Cached - Memory cached object representation of a single row in a database table.

SYNOPSIS

package Category;

use Rose::DB::Object::Cached;
our @ISA = qw(Rose::DB::Object::Cached);

__PACKAGE__->meta->table('categories');

__PACKAGE__->meta->columns
(
  id          => { type => 'int', primary_key => 1 },
  name        => { type => 'varchar', length => 255 },
  description => { type => 'text' },
);

__PACKAGE__->meta->add_unique_key('name');

__PACKAGE__->meta->initialize;

...

$cat1 = Category->new(id   => 123,
                      name => 'Art');

$cat1->save or die $category->error;


$cat2 = Category->new(id => 123);

# This will load from the memory cache, not the database
$cat2->load or die $cat2->error; 

# $cat2 is the same object as $cat1
print "Yep, cached"  if($cat1 eq $cat2);

# No, really, it's the same object
$cat1->name('Blah');
print $cat2->name; # prints "Blah"

...

DESCRIPTION

Rose::DB::Object::Cached is a subclass of Rose::DB::Object that is backed by a write-through memory cache. Whenever an object is loaded from or saved to the database, it is cached in memory. Any subsequent attempt to load an object of the same class with the same primary key or unique key value(s) will give you the cached object instead of loading from the database.

This means that modifications to an object will also modify all other objects in memory that have the same primary key. The synopsis above highlights this fact.

This class is most useful for encapsulating "read-only" rows, or other data that is updated very infrequently. In the Category example above, it would be inefficient to repeatedly load category information in a long-running process (such as a mod_perl Apache web server) if that information changes infrequently.

The memory cache can be cleared for an individual object or all objects of the same class. There is no automatic cache expiration, however. You must clear the cache manually as you see fit.

Only the methods that are overridden are documented here. See the Rose::DB::Object documentation for the rest.

CLASS METHODS

forget_all

Clear the memory cache for all objects of this class.

OBJECT METHODS

forget

Delete the current object from the memory cache.

forget_all

Clear the memory cache for all objects of this class.

load [PARAMS]

Load an object based on either a primary key or a unique key.

If the object exists in the memory cache, the current object "becomes" the cached object. See the synopsis or description above for more information.

If the object is not in the memory cache, it is loaded from the database. If the load succeeds, it is also written to the memory cache.

PARAMS are name/value pairs, and are optional. Valid parameters are:

• refresh

  If set to a true value, then the data is always loaded from the database rather than from the memory cache. If the load succeeds, the object replaces whatever was in the cache. If it fails, the cache is not modified.

Returns true if the object was loaded successfully, false if the row could not be loaded or did not exist in the database.

remember

Save the current object to the memory cache without saving it to the database as well.

save [PARAMS]

This method does the same thing as the Rose::DB::Object method of the same name, except that it also saves the object to the memory cache if the save succeeds. If it fails, the memory cache is not modified.

RESERVED METHODS

In addition to the reserved methods listed in the Rose::DB::Object documentation, the following method names are also reserved for objects that inherit from this class:

forget
forget_all
remember

AUTHOR

John C. Siracusa (siracusa@mindspring.com)

COPYRIGHT

Copyright (c) 2005 by John C. Siracusa. All rights reserved. This program is free software; you can redistribute it and/or modify it under the same terms as Perl itself.