NAME
Data::ObjectDriver - Simple, transparent data interface, with caching
SYNOPSIS
## Set up your database driver code.
package FoodDriver;
sub driver {
Data::ObjectDriver::Driver::DBI->new(
dsn => 'dbi:mysql:dbname',
username => 'username',
password => 'password',
)
}
## Set up the classes for your recipe and ingredient objects.
package Recipe;
use base qw( Data::ObjectDriver::BaseObject );
__PACKAGE__->install_properties({
columns => [ 'recipe_id', 'title' ],
datasource => 'recipe',
primary_key => 'recipe_id',
driver => FoodDriver->driver,
});
package Ingredient;
use base qw( Data::ObjectDriver::BaseObject );
__PACKAGE__->install_properties({
columns => [ 'ingredient_id', 'recipe_id', 'name', 'quantity' ],
datasource => 'ingredient',
primary_key => [ 'recipe_id', 'ingredient_id' ],
driver => FoodDriver->driver,
});
## And now, use them!
my $recipe = Recipe->new;
$recipe->title('Banana Milkshake');
$recipe->save;
my $ingredient = Ingredient->new;
$ingredient->recipe_id($recipe->id);
$ingredient->name('Bananas');
$ingredient->quantity(5);
$ingredient->save;
## Needs more bananas!
$ingredient->quantity(10);
$ingredient->save;
## Shorthand constructor
my $ingredient = Ingredient->new(recipe_id=> $recipe->id,
name => 'Milk',
quantity => 2);DESCRIPTION
Data::ObjectDriver is an object relational mapper, meaning that it maps object-oriented design concepts onto a relational database.
It's inspired by, and descended from, the MT::ObjectDriver classes in Six Apart's Movable Type and TypePad weblogging products. But it adds in caching and partitioning layers, allowing you to spread data across multiple physical databases, without your application code needing to know where the data is stored.
It's currently considered ALPHA code. The API is largely fixed, but may seen some small changes in the future. For what it's worth, the likeliest area for changes are in the syntax for the search method, and would most likely not break much in the way of backwards compatibility.
METHODOLOGY
Data::ObjectDriver provides you with a framework for building database-backed applications. It provides built-in support for object caching and database partitioning, and uses a layered approach to allow building very sophisticated database interfaces without a lot of code.
You can build a driver that uses any number of caching layers, plus a partitioning layer, then a final layer that actually knows how to load data from a backend datastore.
For example, the following code:
my $driver = Data::ObjectDriver::Driver::Cache::Memcached->new(
cache => Cache::Memcached->new(
servers => [ '127.0.0.1:11211' ],
),
fallback => Data::ObjectDriver::Driver::Partition->new(
get_driver => \&get_driver,
),
);creates a new driver that supports both caching (using memcached) and partitioning.
It's useful to demonstrate the flow of a sample request through this driver framework. The following code:
my $ingredient = Ingredient->lookup([ $recipe->recipe_id, 1 ]);would take the following path through the Data::ObjectDriver framework:
The caching layer would look up the object with the given primary key in all of the specified memcached servers.
If the object was found in the cache, it would be returned immediately.
If the object was not found in the cache, the caching layer would fall back to the driver listed in the fallback setting: the partitioning layer.
The partitioning layer does not know how to look up objects by itself--all it knows how to do is to give back a driver that does know how to loko up objects in a backend datastore.
In our example above, imagine that we're partitioning our ingredient data based on the recipe that the ingredient is found in. For example, all of the ingredients for a "Banana Milkshake" would be found in one partition; all of the ingredients for a "Chocolate Sundae" might be found in another partition.
So the partitioning layer needs to tell us which partition to look in to load the ingredients for $recipe->recipe_id. If we store a partition_id column along with each $recipe object, that information can be loaded very easily, and the partitioning layer will then instantiate a DBI driver that knows how to load an ingredient from that recipe.
Using the DBI driver that the partitioning layer created, Data::ObjectDriver can look up the ingredient with the specified primary key. It will return that key back up the chain, giving each layer a chance to do something with it.
The caching layer, when it receives the object loaded in Step 3, will store the object in memcached.
The object will be passed back to the caller. Subsequent lookups of that same object will come from the cache.
HOW IS IT DIFFERENT?
Data::ObjectDriver differs from other similar frameworks (e.g. Class::DBI) in a couple of ways:
It has built-in support for caching.
It has built-in support for data partitioning.
Drivers are attached to classes, not to the application as a whole.
This is essential for partitioning, because your partition drivers need to know how to load a specific class of data.
But it can also be useful for caching, because you may find that it doesn't make sense to cache certain classes of data that change constantly.
The driver class != the base object class.
All of the object classes you declare will descend from Data::ObjectDriver::BaseObject, and all of the drivers you instantiate or subclass will descend from Data::ObjectDriver itself.
This provides a useful distinction between your data/classes, and the drivers that describe how to act on that data, meaning that an object based on Data::ObjectDriver::BaseObject is not tied to any particular type of driver.
USAGE
Class->lookup($id)
Looks up/retrieves a single object with the primary key $id, and returns the object.
$id can be either a scalar or a reference to an array, in the case of a class with a multiple column primary key.
Class->lookup_multi(\@ids)
Looks up/retrieves multiple objects with the IDs \@ids, which should be a reference to an array of IDs. As in the case of lookup, an ID can be either a scalar or a reference to an array.
Returns a reference to an array of objects in the same order as the IDs you passed in. Any objects that could not successfully be loaded will be represented in that array as an undef element.
So, for example, if you wanted to load 2 objects with the primary keys [ 5, 3 ] and [ 4, 2 ], you'd call lookup_multi like this:
Class->lookup_multi([
[ 5, 3 ],
[ 4, 2 ],
]);And if the first object in that list could not be loaded successfully, you'd get back a reference to an array like this:
[
undef,
$object
]where $object is an instance of Class.
Class->search(\%terms [, \%options ])
Searches for objects matching the terms %terms. In list context, returns an array of matching objects; in scalar context, returns a reference to a subroutine that acts as an iterator object, like so:
my $iter = Ingredient->search({ recipe_id => 5 });
while (my $ingredient = $iter->()) {
...
}The keys in %terms should be column names for the database table modeled by Class (and the values should be the desired values for those columns).
%options can contain:
sort
The name of a column to use to sort the result set.
Optional.
direction
The direction in which you want to sort the result set. Must be either
ascendordescend.Optional.
limit
The value for a LIMIT clause, to limit the size of the result set.
Optional.
offset
The offset to start at when limiting the result set.
Optional.
fetchonly
A reference to an array of column names to fetch in the SELECT statement.
Optional; the default is to fetch the values of all of the columns.
for_update
If set to a true value, the SELECT statement generated will include a FOR UPDATE clause.
Class->add_trigger($trigger, \&callback)
Adds a trigger to all objects of class Class, such that when the event $trigger occurs to any of the objects, subroutine &callback is run. Note that triggers will not occur for instances of subclasses of Class, only of Class itself. See TRIGGERS for the available triggers.
Class->call_trigger($trigger, [@callback_params])
Invokes the triggers watching class Class. The parameters to send to the callbacks (in addition to Class) are specified in @callback_params. See TRIGGERS for the available triggers.
$obj->save
Saves the object $obj to the database.
If the object is not yet in the database, save will automatically generate a primary key and insert the record into the database table. Otherwise, it will update the existing record.
If an error occurs, save will croak.
Internally, save calls update for records that already exist in the database, and insert for those that don't.
$obj->remove
Removes the object $obj from the database.
If an error occurs, remove will croak.
Class->remove(\%terms, \%args)
Removes objects found with the %terms. So it's a shortcut of:
my @obj = Class->search(\%terms, \%args);
for my $obj (@obj) {
$obj->remove;
}However, when you pass nofetch option set to %args, it won't create objects with search, but issues DELETE SQL directly to the database.
## issues "DELETE FROM tbl WHERE user_id = 2"
Class->remove({ user_id => 2 }, { nofetch => 1 });This might be much faster and useful for tables without Primary Key, but beware that in this case Triggers won't be fired because no objects are instanciated.
Class->bulk_insert([col1, col2], [[d1,d2], [d1,d2]]);
Bulk inserts data into the underlying table. The first argument is an array reference of columns names as specified in install_properties
$obj->add_trigger($trigger, \&callback)
Adds a trigger to the object $obj, such that when the event $trigger occurs to the object, subroutine &callback is run. See TRIGGERS for the available triggers. Triggers are invoked in the order in which they are added.
$obj->call_trigger($trigger, [@callback_params])
Invokes the triggers watching all objects of $obj's class and the object $obj specifically for trigger event $trigger. The additional parameters besides $obj, if any, are passed as @callback_params. See TRIGGERS for the available triggers.
TRIGGERS
Data::ObjectDriver provides a trigger mechanism by which callbacks can be called at certain points in the life cycle of an object. These can be set on a class as a whole or individual objects (see USAGE).
Triggers can be added and called for these events:
pre_save -> ($obj, $orig_obj)
Callbacks on the pre_save trigger are called when the object is about to be saved to the database. For example, use this callback to translate special code strings into numbers for storage in an integer column in the database. Note that this hook is also called when you
removethe object.Modifications to $obj will affect the values passed to subsequent triggers and saved in the database, but not the original object on which the save method was invoked.
post_save -> ($obj, $orig_obj)
Callbaks on the post_save triggers are called after the object is saved to the database. Use this trigger when your hook needs primary key which is automatically assigned (like auto_increment and sequence). Note that this hooks is NOT called when you remove the object.
pre_insert/post_insert/pre_update/post_update/pre_remove/post_remove -> ($obj, $orig_obj)
Those triggers are fired before and after $obj is created, updated and deleted.
post_load -> ($obj)
Callbacks on the post_load trigger are called when an object is being created from a database query, such as with the lookup and search class methods. For example, use this callback to translate the numbers your pre_save callback caused to be saved back into string codes.
Modifications to $obj will affect the object passed to subsequent triggers and returned from the loading method.
Note pre_load should only be used as a trigger on a class, as the object to which the load is occuring was not previously available for triggers to be added.
pre_search -> ($class, $terms, $args)
Callbacks on the pre_search trigger are called when a content addressed query for objects of class $class is performed with the search method. For example, use this callback to translate the entry in $terms for your code string field to its appropriate integer value.
Modifications to $terms and $args will affect the parameters to subsequent triggers and what objects are loaded, but not the original hash references used in the search query.
Note pre_search should only be used as a trigger on a class, as search is never invoked on specific objects.
The return values from your callbacks are ignored.
Note that the invocation of callbacks is the responsibility of the object driver. If you implement a driver that does not delegate to Data::ObjectDriver::Driver::DBI, it is your responsibility to invoke the appropriate callbacks with the call_trigger method.
PROFILING
For performance tuning, you can turn on query profiling by setting $Data::ObjectDriver::PROFILE to a true value. Or, alternatively, you can set the DOD_PROFILE environment variable to a true value before starting your application.
To obtain the profile statistics, get the global Data::ObjectDriver::Profiler instance:
my $profiler = Data::ObjectDriver->profiler;Then see the documentation for Data::ObjectDriver::Profiler to see the methods on that class.
EXAMPLES
A Partitioned, Caching Driver
package Ingredient;
use strict;
use base qw( Data::ObjectDriver::BaseObject );
use Data::ObjectDriver::Driver::DBI;
use Data::ObjectDriver::Driver::Partition;
use Data::ObjectDriver::Driver::Cache::Cache;
use Cache::Memory;
use Carp;
our $IDs;
__PACKAGE__->install_properties({
columns => [ 'ingredient_id', 'recipe_id', 'name', 'quantity', ],
datasource => 'ingredients',
primary_key => [ 'recipe_id', 'ingredient_id' ],
driver =>
Data::ObjectDriver::Driver::Cache::Cache->new(
cache => Cache::Memory->new( namespace => __PACKAGE__ ),
fallback =>
Data::ObjectDriver::Driver::Partition->new(
get_driver => \&get_driver,
pk_generator => \&generate_pk,
),
),
});
sub get_driver {
my($terms) = @_;
my $recipe;
if (ref $terms eq 'HASH') {
my $recipe_id = $terms->{recipe_id}
or Carp::croak("recipe_id is required");
$recipe = Recipe->lookup($recipe_id);
} elsif (ref $terms eq 'ARRAY') {
$recipe = Recipe->lookup($terms->[0]);
}
Carp::croak("Unknown recipe") unless $recipe;
Data::ObjectDriver::Driver::DBI->new(
dsn => 'dbi:mysql:database=cluster' . $recipe->cluster_id,
username => 'foo',
pk_generator => \&generate_pk,
);
}
sub generate_pk {
my($obj) = @_;
$obj->ingredient_id(++$IDs{$obj->recipe_id});
1;
}
1;LICENSE
Data::ObjectDriver is free software; you may redistribute it and/or modify it under the same terms as Perl itself.
AUTHOR & COPYRIGHT
Except where otherwise noted, Data::ObjectDriver is Copyright 2005-2006 Six Apart, cpan@sixapart.com. All rights reserved.