Delete child entity when modifying parent entity - symfony

Question

I'm working in modify file action in my controller. Child entity(StrOrigin) has the following relationship with File entity:
/**
* #ORM\ManyToOne(targetEntity="File" )
* #ORM\JoinColumn(name="STOR_FILE", referencedColumnName="id", onDelete="CASCADE")
*/
Now in my modify action in the controller, I get the file to modify, set the form and do some tests then upload the file, persist file entity and override the StrOrigin (which is many strings from file) with the new modified file. I'm stuck in how to override the StrOrigin. I've tried deleting the old file when submitting and persisting the new one:
$this_file_STROR=$em->getRepository('File')->find(array('id'=>$idfile));
$em->remove($this_file_STROR);
$em->flush();
But that didn't seem to work.

Answer 1

Following up on the comments:
You don't want to remove your actual file. You are misinterpreting the onDelete="CASCADE"! It means that when you delete a file, all StrOrigin will also get deleted. It has nothing to do with what you want to achieve.
What you want is the following:
$this_file_STROR=$em->getRepository('File')->find($idfile);
foreach($this_file_STROR->getStrOrigins() AS $strOrigin){
$em->remove($strOrigin);
}
// now $this_file_STROR as no StrOrigins anymore
$em->flush();
Also note that you don't need to flush at this point. A flush is simply persisting your current objects to the database. As long as you work with the objects, there is no need to flush. Normally you can flush right before your script ends, e.g. before you call render in your controller. If you flush several times, your application may be slow due to interaction with the database.

Answer 2

I found another solution which may be much faster:
It's described here and is called orphan removal. The idea is to simply remove the association and tell doctrine that related entities which are not refered to anymore shall be removed. In your case, you would do the following:
/**
* #ORM\ManyToOne(targetEntity="File" )
* #ORM\JoinColumn(name="STOR_FILE", referencedColumnName="id", orphanRemoval=true)
*/
public function deleteStrOrigins(){
$this->strOrigins = new ArrayCollection(); // you can also try to use = null. I'm using ArrayCollections, so this is my way and I never tried the null approach.
}
Now calling in your code
$this_file_STROR=$em->getRepository('File')->find($idfile);
$this_file_STROR->deleteStrOrigins();
$em->flush();
should delete all related StrOrigins as long as they are not related anywhere else.