Bug Report

Summary

The order in which the UoW wants to delete children is somehow missing a dependency when there is an association to the same class even if you specified cascade: ['remove'].
Given you have

• Parent -> has an association to children with cascade: ['remove']
• Child 1
• Child 2 -> has an association to Child 1 with cascade: ['remove'].

Now you delete the parent.
Doctrine tries to remove Child 1 first instead of Child 2 causing a foreign constraint violation:

Uncaught PDOException: SQLSTATE[23000]: Integrity constraint violation: 1451 Cannot delete or update a parent row: a foreign key constraint fails (test.child_entities, CONSTRAINT FK_DAEB194156A273CC FOREIGN KEY (origin_id) REFERENCES child_entities (id))

How to reproduce

I've created a test setup because I'm not familiar with the internals of ORM at all. So here we go:

1. Clone https://github.com/Toflar/doctrine-orm-bug-reproducer
2. Run composer install
3. Adjust dummy mysql connection example in bootstrap.php.
4. Run bin/doctrine orm:schema-tool:drop --force && bin/doctrine orm:schema-tool:create
5. Run php test.php.

Expected behavior

It should not throw an exception. Doctrine should remove Child 2 first.