I was tweeting something about having separate “DDD” and “ORM” entities in a project in a project, and that I don’t understand this. There were some great comments and questions, thanks a lot for that! To be honest, I understand more about it now. In this article I’ll try to provide some more information about this.

I’m glad many developers want to use input from the book “Domain-Driven Design” by Eric Evans to improve their domain model. I recommend reading this book and getting your information from the source, because unfortunately the internet, tweets, e-books, including my own books, aren’t able to reflect a full, nor a correct view of everything there is to find out about this topic. All too often DDD is completely misinterpreted to be “an elitist, dogmatic approach to programming, where we use DTOs, layers, and CQRS”…

I’d like to start this article with a quote from Ross Tuck’s article “Persisting Value Objects in Doctrine”. He describes different ways of persisting value objects when using Doctrine ORM. At the end of the page he gives us the following option - the “nuclear” one:

[…] Doctrine is great for the vast majority of applications but if you’ve got edge cases that are making your entity code messy, don’t be afraid to toss Doctrine out. Setup an interface for your repositories and create an alternate implementation where you do the querying or mapping by hand. It might be a PITA but it might also be less frustration in the long run.

It appears that I didn’t make myself clear while writing about entity managers and manager registries yesterday. People were quick to reply that instead you should inject entity repositories. However, I wasn’t talking about entity repositories here. I was talking about classes that get an EntityManager injected because they want to call persist() or flush(). The point of my previous post was that in those cases you should inject the manager registry, because you don’t know beforehand which entity manager manages the entities you are trying to persist. By injecting a manager registry you also make your code useful in contexts where another Doctrine persistence library is used.

Please also read my next article about injecting entity managers.

Or: how to make your persistence-related code more reusable

You probably know that you should trim your controllers as much as possible. This usually means extracting some classes from the semi-procedural code inside your controller class. You create services for the extracted classes and inject the necessary dependencies into them. You can no longer use the convenient $this->getDoctrine()->getManager(). Instead you inject the doctrine.orm.default_entity_manager service into every service that needs the EntityManager to persist data in your relational database: