Symfony2 QueryBuilder join ON and WITH difference

Question

I'm new with Symfony2 and I built successfully my first join through QueryBuilder and Doctrine 2. Probably this is a stupid question but both on-line and in the Symfony2's methods I was unable to find anything for understanding the difference between the join clauses "WITH" and "ON".

For example this is my join code:

->leftJoin('EcommerceProductBundle:ProductData', 'pdata', 'WITH', 'prod.id = IDENTITY(pdata.product)')

It works good but if I put ON instead of WITH I get the following error:

[Syntax Error] line 0, col 200: Error: Expected Doctrine\ORM\Query\Lexer::T_WITH, got 'ON'

Why? I've seen among the objects that there are both the T_ON and T_WITH like join clauses, but which is their usage difference? What is their uses like?

Answer 1

@florian gave you the correct answer but let me try to explain it on example:

In sql, joins are done like this:

SELECT * FROM category
    LEFT JOIN product ON product.category_id = category.id

(or something like this)

Now in Doctrine, you don't need to use ON clause because doctrine knows that from relations annotations in your entities. So above example would be:

// CategoryRepository.php
public function getCategoriesAndJoinProducts() 
{
    return $this->createQueryBuilder("o")
        ->leftJoin("o.products", "p")->addSelect("p") 
        ->getQuery()->getResult() ;
}

Both would fetch all categories and join products associated with them.

Now comes the WITH clause. If you want to join only products with price bigger than 50, you would do this in SQL:

SELECT * FROM category
    LEFT JOIN product ON product.category_id = category.id AND product.price>50

In Doctrine:

// CategoryRepository.php
public function getCategoriesAndJoinProductsWithPriceBiggerThan($price) 
{
    return $this->createQueryBuilder("o")
        ->leftJoin("o.products", "p", "WITH", "p.price>:price")
            ->setParameter("price", price)->addSelect("p") 
        ->getQuery()->getResult() ;
}

So, in reality you should never, ever use ON if you are using Doctrine. If you have a need for something like that, you can be almost sure that you screwed something else.

Answer 2

In theory, ON permits you to give the full join criterias, while WITH permits to add additional criterias to the default ones (IMHO).

But, what DQL permits is to avoid giving the JOIN criterias:

You just have to say: $qb->leftJoin('prod.pdata', 'pdata');

And doctrine2 will handle the join correctly.

Here is a related question about that: Can I use "ON" keyword in DQL or do I need to use Native Query?