Remove rows from child table with Class Table Inheritance in Doctrine - php

Question

I have made a really basic example with two models.
"Singer" extends from "Person"
I am using class table Inheritance with these two models:
<?php
namespace models;
/**
* #Table(name="persons")
* #entity
* #InheritanceType("JOINED")
* #DiscriminatorColumn(name="type", type="string")
* #DiscriminatorMap({"singer" = "\models\Singer"})
*/
abstract class Person {
/**
* #Id
* #Column(type="integer", nullable=false, name="id_person")
* #GeneratedValue(strategy="AUTO")
*/
protected $id;
/** #column(type="string", nullable=false) */
protected $name;
The singer model looks like:
namespace models;
/**
* #Table(name="singers")
* #entity
*/
class Singer extends Person{
/** #column(type="string", nullable=false) */
protected $gender;
}
Workflow
Consider this scenario.
In the db I have these rows:
persons table:
id_person | name | type
-----------------------
1 john singer
singers table:
id_person | gender
------------------
1 pop
I proceed to remove this singer:
$singer = $em->find('models\Singer', 1);
$em->remove($singer);
$em->flush();
After execute the code above, I check again the database and I found this:
persons table:
id_person | name | type
-----------------------
(empty)
singers table:
id_person | gender
------------------
1 pop
As you note, the row from child table was not removed as expected.
So, after searching in doctrine's documentation, it states:
When you do not use the SchemaTool to generate the required SQL you should know that deleting a class table inheritance makes use of the foreign key property ON DELETE CASCADE in all database implementations. A failure to implement this yourself will lead to dead rows in the database.
So, I proceed to alter persons table as below:
ALTER TABLE persons
ADD CONSTRAINT fk_persons_1
FOREIGN KEY (id_person)
REFERENCES singers (id_person)
ON DELETE CASCADE
ON UPDATE NO ACTION;
Now, the problems get complicated:
when I remove a singer, the information still there, even the persons table was altered in order to delete from singers table too.
When I try to insert a new singer like
$singer = new \models\Singer('Zara', 'rock');
$em->persist($singer);
$em->flush();
it throws an exception:
Fatal error: Uncaught exception 'PDOException' with message 'SQLSTATE[23000]: Integrity constraint violation: 1452 Cannot add or update a child row: a foreign key constraint fails (`practica`.`persons`, CONSTRAINT `fk_persons_1` FOREIGN KEY (`id_person`) REFERENCES `singers` (`id_person`) ON DELETE CASCADE ON UPDATE NO ACTION)' in /var/www/html/doctrine/vendor/doctrine/dbal/lib/Doctrine/DBAL/Statement.php:138 Stack trace: #0 /var/www/html/doctrine/vendor/doctrine/dbal/lib/Doctrine/DBAL/Statement.php(138): PDOStatement->execute(NULL) #1 /var/www/html/doctrine/vendor/doctrine/orm/lib/Doctrine/ORM/Persisters/JoinedSubclassPersister.php(165): Doctrine\DBAL\Statement->execute() #2 /var/www/html/doctrine/vendor/doctrine/orm/lib/Doctrine/ORM/UnitOfWork.php(929): Doctrine\ORM\Persisters\JoinedSubclassPersister->executeInserts() #3 /var/www/html/doctrine/vendor/doctrine/orm/lib/Doctrine/ORM/UnitOfWork.php(318): Doctrine\ORM\UnitOfWork->executeInserts(Object(Doctrine\ORM\Mapping\ClassMetadata)) #4 /var/www/html/doctrine/vendor/doct in /var/www/html/doctrine/vendor/doctrine/dbal/lib/Doctrine/DBAL/DBALException.php on line 47
So, basically, all I need is to remove the information in child table too in MySQL db. But I do not get it.

Answer 1

Try reversing the FOREIGN KEY i.e. remove it from your persons table and add it to your singers table
ALTER TABLE singers
ADD CONSTRAINT fk_singers_1
FOREIGN KEY (id_person)
REFERENCES persons (id_person)
ON DELETE CASCADE
ON UPDATE NO ACTION;

Answer 2

I think you probably have to ask yourself if you really need a field relating to multiple tables.
In any case, maybe is better to do it through a relation instead of using inheritance and a discriminator map, that works well with objects using the same table, but since in your case they are different tables it is probably better to use a relation instead:
<?php
namespace models;
/**
* #Table(name="persons")
* #entity
*/
class Person {
/**
* #Id
* #Column(type="integer", nullable=false, name="id_person")
* #GeneratedValue(strategy="AUTO")
*/
protected $id;
/** #column(type="string", nullable=false) */
protected $name;
/**
* #OneToOne(targetEntity="Singer")
* #JoinColumn(name="id_person", referencedColumnName="id_person")
*/
private $singer;
namespace models;
/**
* #Table(name="singers")
* #entity
*/
class Singer{
/**
* #Id
* #Column(type="integer", nullable=false, name="id_person")
* #GeneratedValue(strategy="AUTO")
*/
protected $id;
/** #column(type="string", nullable=false) */
protected $gender;
/**
* #OneToOne(targetEntity="Person", cascade={"persist", "remove", "merge"}, orphanRemoval=true)
* #JoinColumn(name="id_person", referencedColumnName="id_person")
*/
private $person;
}
By trying to attach the design to the real world you are over complicating the implementation which will make your application hard to mantain.
I did not try the code (probably needs adjustement).