My understanding of how ORM persist works:

//ORM "persist" oversimplification
function persist(&$entity)
{
    ...
    $insertId = api_actual_db_insert(...);
    $entity->setId($insertId);
}

//usage of ORM later ...
$this->getEntityManager()->persist($entity);
print $entity->getId();  //prints ID of newly inserted record

But why not ..

function persist($entity)
{
    ...
    $insertId = api_actual_db_insert(...);
    return $insertId;
}

//later ...
$insertId = $this->getEntityManager()->persist($entity);
$entity->setId($insertId);
print $entity->getId();

Both ways work. My issue is with “references”. I can perhaps see a little bit why and what the reasoning is behind why ORMs work this way .., but my question stems from writing my own similar domain specific functionality that I have decided to mimic after the ORM concepts and I am having “issues” with using references. Not technical issues but moral and computer sciency-issues as far as reasoning and rationale for using them in this context.

To be precise, examining Doctrine’s own code (my choice of ORM), I did not see an explicit Entity reference being passed, so the mechanics of an ORM may use some other different technique. My question will stand though regardless of the method. What’s of interest to me is that Entity is populated with the insert_id, and insert_id is not returned explicitly.

My code

I have a concept of Selection object that contains a lot of stuff. Maybe later it may become a true Entity, but right now it’s not (lots of refactoring work to be done before it is ready), so I have to manage it manually, without ORM backing. I wrote my own persist function that is similar and my question is basically what I’ve already stated above. I may understand why an ORM works this way but I do not understand if I should implement my own storage the same way or not.

Question

To be explicit … is there any particular or specific reason why an ORM would use this specific technique of populating Entity with insert_id without an explicit return statement, opposed to returning insert_id explicitly via return statement to the caller? If I do choose to return insert_id explicitly, what will I be missing/breaking?