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"

  # The object cache supports time-based expiration
  Category->meta->cached_objects_expire_in('15 minutes');

  $cat1 = Category->new(id => 123);
  $cat1->save or $cat1->die;

  $cat1->load; # loaded from cache

  $cat2 = Category->new(id => 123);
  $cat2->load; # loaded from cache

  <15 minutes pass>

  $cat3 = Category->new(id => 123);
  $cat3->load; # NOT loaded from cache

  ...

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 also support for simple time-based cache expiration. See the clear_object_cache and cached_objects_expire_in methods in the Rose::DB::Object::Metadata documentation for more information.

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

OBJECT METHODS

delete [PARAMS]

This method works like the delete method from Rose::DB::Object except that it also calls the forget method if the object was deleted successfully or did not exist in the first place.

forget

Delete the current object from the memory cache.

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. The true value returned on success will be the object itself. If the object overloads its boolean value such that it is not true, then a true value will be returned instead of the object itself.

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
    remember

If you have a column with one of these names, you must alias it. See the Rose::DB::Object documentation for more information on column aliasing and reserved methods.

AUTHOR

John C. Siracusa (siracusa@mindspring.com)

COPYRIGHT

Copyright (c) 2006 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.