Symfony 3/Doctrine: Sorting by non-persistent columns - doctrine

Question

I have two Models that are related to each other:
class Product
{
//...
/**
* #var Collection<Key>
* One Product has Many Keys.
* #ORM\OneToMany(targetEntity="Key", mappedBy="product")
*/
private $keys;
public function getKeyNumber()
{
return count($this->keys);
}
//...
}
class Key
{
//...
/**
* #var Product
*
* Many Keys have One Product.
* #ORM\ManyToOne(targetEntity="Product", inversedBy="keys")
* #ORM\JoinColumn(referencedColumnName="id")
*/
private $product;
/**
* #var int
* #ORM\Column(type="integer")
*/
private $product_id;
//...
}
I am able to get the number of Keys with Product::getKeyNumber(). Now I'd like to use this value for sorting in the query.
I've tried something like that (DQL Query):
SELECT a, COUNT(a.keys) AS keyNumber FROM AppBundle\Entity\Product a ORDER BY keyNumber ASC;
which returns:
[Semantical Error] line 0, col 18 near 'keys) AS keyNumber': Error: Invalid PathExpression. StateFieldPathExpression or SingleValuedAssociationField expected.
When I try:
SELECT a FROM AppBundle\Entity\Product a ORDER BY count(a.keys) ASC
it says:
[Syntax Error] line 0, col 50: Error: Expected known function, got 'count'
Any ideas? :)
Thanks.

Answer 1

You can try doing something like this (just an idea, not a verified code)
SELECT a, COUNT(b.id) AS keyNumber FROM AppBundle:Product a JOIN a.keys b ORDER BY keyNumber ASC;
As soon as COUNT() expects single value field you can explicitly join the keys table and count on something in it (I assume it has ID or you can use whatever is there).

Answer 2

I wonder if it has to do with composite keys? I read something about that. I don't know what your key identifier is, but I show a.id below. Can you try this:
SELECT IDENTITY(a.id), a, COUNT(a.keys) AS keyNumber FROM AppBundle:Product a ORDER BY keyNumber ASC
Note, I've reduced AppBundle\Entity\Product to simply AppBundle:Product and got rid of the semicolon at the end.
Let me know if that works, it may not.