Symfony3 - Delete Entity with OneToMany - relationship in Doctrine - cascade not working - symfony

Question

I have two entities:
/**
* Course
*
* #ORM\Table()
* #ORM\Entity(repositoryClass="AppBundle\Entity\Repository\CourseRepository")
*/
class Course
{
/**
* #var integer
*
* #ORM\Column(name="id", type="integer")
* #ORM\Id
* #ORM\GeneratedValue(strategy="AUTO")
*/
private $id;
/**
* #var \Doctrine\Common\Collections\ArrayCollection()
*
* #ORM\OneToMany(targetEntity="AppBundle\Entity\TimeTableEntry", mappedBy="course", cascade={"remove"}, orphanRemoval=true)
*
*/
private $timeTableEntries;
/**
* #var boolean
*
* #ORM\Column(name="enabled", type="boolean", nullable=true)
*/
private $enabled;
and
/**
* TimeTableEntry
*
* #ORM\Table()
* #ORM\Entity(repositoryClass="AppBundle\Entity\Repository\TimeTableEntryRepository")
*/
class TimeTableEntry
{
/**
* #var integer
*
* #ORM\Column(name="id", type="integer")
* #ORM\Id
* #ORM\GeneratedValue(strategy="AUTO")
*/
private $id;
/**
* #var \Doctrine\Common\Collections\ArrayCollection()
*
* #ORM\ManyToOne(targetEntity="AppBundle\Entity\Course", inversedBy="timeTableEntries", cascade={"ALL"})
* #ORM\JoinColumn(name="course_id", referencedColumnName="id", nullable=true, onDelete="CASCADE")
*/
private $course;
As you can see I tried with cascade={"ALL"}, onDelete="CASCADE" and orphanRemoval=true.
When I want to delete the Course Entity I get the error message:
SQLSTATE[23000]: Integrity constraint violation: 1451 Cannot delete or
update a parent row: a foreign key constraint fails
(edutalk.teaching_event, CONSTRAINT FK_F2B1088B57042871 FOREIGN
KEY (time_table_entry_id) REFERENCES time_table_entry (id))
What can I try to resolve this?

Answer 1

I cannot comment on your post, so I post it as an answer.
Your problem is that you have another entity TeachingEvent with a reference to TimeTableEntry. When you try to delete a TimeTableEntry, it is impossible because this time_table_entry_id is still referenced as a foreign key in the TeachingEvent table.
Before deleting the TimeTableEntry, first you should unlink it from the TeachingEvent. I don't have your code, but depending on how TimeTableEntry and TeachingEvent relate to each other, it's probably something like:
$teachingEvent->setTimeTableEntry(null);
or
$timeTableEntry->setTeachingEvent(null);