Doctrine ORM - Find Many to Many Objects Without a Relationship

Hmmm, does the title of this post make sense? Probably not but it’s not an easy concept to squeeze into a few words. Here’s the scenario, I have two tables A and B in Doctrine ORM with a many-to-many relationship defined in table AB. Now, I want to find all objects in A that do not have a relationship with an object in B via AB. Here’s what I have:

Doctrine_Query::create()
    ->from( 'A a' )
    ->leftJoin( 'A.AB ab' )
    ->where( 'ab.id IS NULL' )
    ->fetchArray()

This works but is it the best way?