Since version 2.2.0, Doctrine ships with a really handy listener, ResolveTargetEntityListener that lets you keep your bundles separated, while still letting you define loose relationships between different entities.

What this listener allows you to do is define a relationship target in your entities that will be replaced at runtime. This becomes very useful when you’ve got different bundles doing different things, and want to have relationships between them, but not defining dependencies between those bundles.

Note that because of the version of Doctrine2 that this listener ships with, you will need to be using Symfony2.1.

Background

In the following example, the situation is we have an InvoiceBundle which provides invoicing functionality, and a CustomerBundle that contains customer management tools. We want to keep these separated, because they can be used in other systems without each other, but for our application we want to use them together.

In this case, we have an Invoice entity with a relationship to a non-existant object, an InvoiceSubjectInterface. The goal is to get the ResolveTargetEntityListener to replace any mention of the interface with a real object that implements that interface.

Set up

We’re going to use the following basic entities (which are incomplete for brevity) to explain how to set up and use the RTEL.

Next, we need to configure the listener. DoctrineBundle lets us configure the listener

Final Thoughts

With the ResolveTargetEntityListener, we are able to decouple our bundles, keeping them usable by themselves, but still being able to define relationships between different objects. By using this method, I’ve found my bundles end up being easier to maintain independently.