Doctrine2 - Cannot delete an entity with a unidirectional oneToMany relation

Question

I'm getting a foreign constraint violation when trying to delete an entity, containing unidirectional one-to-many associations. I have the following simple class:

class Dealer{

/**
 * @ManyToMany(targetEntity="Car", cascade={"persist", "remove"})
 * @JoinTable(name="dealer_cars",
 *      joinColumns={@JoinColumn(name="dealer_id", referencedColumnName="id")},
 *      inverseJoinColumns={@JoinColumn(name="car_id", referencedColumnName="id",
        unique=true)}
 *    )
 **/
  protected cars;
}

The Car object should not contain a relation to its owner in this case (hence the unidirectional relationship). If I try to delete a Dealer object containing associations to cars, I get the following constraint violation:

Cannot delete or update a parent row: a foreign key constraint fails 
(`application`.`dealer_cars`, CONSTRAINT `FK_E1BCEEEBC3C6F69F`
 FOREIGN KEY (`car_id`) REFERENCES `car` (`id`))'

I would get the same message if I tried to delete the dealer row manually from the database table, but I thought Doctrine, using cascade="remove", would take care of this for me.

If I change the association to a bidirectional association it works. Why does this not work with unidirectional associations?

unidirectional one-to-many associations ? this looks more like bi-directional many-to-many to me :D Did you drop your database and recreate or did you have any fixtures/data-leftovers in the database when you changed the schema ? — Nicolai Fröhlich, May 28 '13 at 00:15
you want to delete the dealer without the car being lost , do i get this right? — Nicolai Fröhlich, May 28 '13 at 00:20
It is Doctrines definition of unidirectional one-to-many. It is a many-to-many with a unique constraint. I want to delete the car, when the dealer is deleted as well. — Frederik Wordenskjold, May 28 '13 at 00:22
But I found the problem. I needed to add a `onDelete="cascade"` attribute to the car_id column in the foreign key table. Which obviously makes sense! Thanks for the interest :) — Frederik Wordenskjold, May 28 '13 at 00:23

score 17 · Accepted Answer · edited May 23 '17 at 12:26

Use the Database level onDelete option with Doctrine

@ORM\JoinColumn(name="dealer_id", referencedColumnName="id",  onDelete="SET NULL")

explanation from here:

CASCADE will propagate the change when the parent changes. (If you delete a row, rows in constrained tables that reference that row will also be deleted, etc.)
SET NULL sets the column value to NULL when a parent row goes away.
RESTRICT causes the attempted DELETE of a parent row to fail.

... update your database schema prior to complaining it's not working :-)

app/console doctrine:schema:update --force

if this is not working due to foreign key errors go the hard way (in this order) :

app/console doctrine:database:drop
app/console doctrine:database:create
app/console doctrine:schema:update --force
( optional: app/console doctrine:fixtures:load )

yeah, this was it. I guess "SET NULL" would work out just as well as "cascade". — Frederik Wordenskjold, May 28 '13 at 00:25

Doctrine2 - Cannot delete an entity with a unidirectional oneToMany relation

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