Doctrine_manual-1-2-en

Chapter 7: Defining Models 95
# ...
relations:
# ...
Addresses:
class: Address
local: id
foreign: user_id
cascade: [delete]
The cascade option is used to specify the operations that are cascaded to the related objects
on the application-level.
Please note that the only currently supported value is delete, more options will be added
in future releases of Doctrine.
In the example above, Doctrine would cascade the deletion of a User to it's associated
Addresses. The following describes the generic procedure when you delete a record through
$record->delete():
1. Doctrine looks at the relations to see if there are any deletion cascades it needs to apply. If
there are no deletion cascades, go to 3).
2. For each relation that has a delete cascade specified, Doctrine verifies that the objects that
are the target of the cascade are loaded. That usually means that Doctrine fetches the related
objects from the database if they're not yet loaded.(Exception: many-valued associations are
always re-fetched from the database, to make sure all objects are loaded). For each
associated object, proceed with step 1).
3. Doctrine orders all deletions and executes them in the most efficient way, maintaining
referential integrity.
From this description one thing should be instantly clear: Application-level cascades happen
on the object-level, meaning operations are cascaded from one object to another and in order
to do that the participating objects need to be available.
This has some important implications:
• Application-level delete cascades don't perform well on many-valued associations
when there are a lot of objects in the related collection (that is because they need to
be fetched from the database, the actual deletion is pretty efficient).
• Application-level delete cascades do not skip the object lifecycle as database-level
cascades do (see next chapter). Therefore all registered event listeners and other
callback methods are properly executed in an application-level cascade.
Database-Level Cascades
Some cascading operations can be done much more efficiently at the database level. The best
example is the delete cascade.
Database-level delete cascades are generally preferrable over application-level delete
cascades except:
• Your database does not support database-level cascades (i.e. when using MySql with
MYISAM tables).
• You have listeners that listen on the object lifecycle and you want them to get
invoked.
Database-level delete cascades are applied on the foreign key constraint. Therefore they're
specified on that side of the relation that owns the foreign key. Picking up the example from
above, the definition of a database-level cascade would look as follows:
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