Joshua Thijssen has a recent post to his site about the MultiParamConverter available for the Symfony 2 framework - a tool he's created to make working with multiple slugs and entities.
If you know Symfony2, you probably are using (or at least, have heard of) the @paramConverter annotation from the SensioFrameworkExtraBundle. This is a really simple way to convert slugs into entities. But lots of times I find myself having multiple slugs inside my routes, and this is something the @paramConverter annotation cannot do. So that's why I've created the multiParamConverter.
To review (or introduce it for those new to it) he talks a bit about the normal "paramConverter" (including a bit of code) and shows how it can replace the fetch of an entity based off a parameter via a DocBlock annotation. Due to the inflexibility of this method, his "MultiParamConverter" lets you define the association for multiple parameters For those that want a peek "under the covers", he includes a section on how it all works and what parts of the framework it uses.