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mirror of synced 2024-12-15 15:46:02 +03:00

Extended details on how to remove entities and their associations

This commit is contained in:
beberlei 2010-07-10 08:33:12 +02:00
parent 50e35e6bdc
commit 1017e2c6c7

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@ -117,6 +117,30 @@ The semantics of the remove operation, applied to an entity X are as follows:
* If X is a removed entity, it is ignored by the remove operation.
* A removed entity X will be removed from the database as a result of the flush operation.
Removing an entity will also automatically delete any exisiting records in many-to-many
join tables that link this entity. The action taken depends on the value of the `@joinColumn`
mapping attribute "onDelete". Either Doctrine issues a dedicated `DELETE` statement
for records of each join table or it depends on the foreign key semantics of
onDelete="CASCADE".
Deleting an object with all its associated objects can be achieved in multiple
ways with very different performance impacts.
1. If an association is marked as `CASCADE=REMOVE` Doctrine 2 will fetch this
association. If its a Single association it will pass this entity to
´EntityManager#remove()`. If the association is a collection, Doctrine will loop over all
its elements and pass them to `EntityManager#remove()`. In both cases the
cascade remove semantics are applied recursively. For large object graphs
this removal strategy can be very costly.
2. Using a DQL `DELETE` statement allows you to delete multiple entities of a
type with a single command and without hydrating these entities. This
can be very efficient to delete large object graphs from the database.
3. Using foreign key semantics `onDelete="CASCADE"` can force the database
to remove all associated objects internally. This strategy is a bit
tricky to get right but can be very powerful and fast. You should be aware
however that using strategy 1 (`CASCADE=REMOVE`) completly by-passes
any foreign key `onDelete=CASCADE` option, because Doctrine will fetch and remove
all associated entities explicitly nevertheless.
++ Detaching entities