Doctrine2: Best way to handle many-to-many with extra columns in reference table

Question

I\'m wondering what\'s the best, the cleanest and the most simply way to work with many-to-many relations in Doctrine2.

Let\'s assume that we\'ve got an album like

Answer 1

I think I would go with @beberlei's suggestion of using proxy methods. What you can do to make this process simpler is to define two interfaces:

interface AlbumInterface {
    public function getAlbumTitle();
    public function getTracklist();
}

interface TrackInterface {
    public function getTrackTitle();
    public function getTrackDuration();
}

Then, both your Album and your Track can implement them, while the AlbumTrackReference can still implement both, as following:

class Album implements AlbumInterface {
    // implementation
}

class Track implements TrackInterface {
    // implementation
}

/** @Entity whatever */
class AlbumTrackReference implements AlbumInterface, TrackInterface
{
    public function getTrackTitle()
    {
        return $this->track->getTrackTitle();
    }

    public function getTrackDuration()
    {
        return $this->track->getTrackDuration();
    }

    public function getAlbumTitle()
    {
        return $this->album->getAlbumTitle();
    }

    public function getTrackList()
    {
        return $this->album->getTrackList();
    }
}

This way, by removing your logic that is directly referencing a Track or an Album, and just replacing it so that it uses a TrackInterface or AlbumInterface, you get to use your AlbumTrackReference in any possible case. What you will need is to differentiate the methods between the interfaces a bit.

This won't differentiate the DQL nor the Repository logic, but your services will just ignore the fact that you're passing an Album or an AlbumTrackReference, or a Track or an AlbumTrackReference because you've hidden everything behind an interface :)

Hope this helps!