DevShed concludes their three-part series about building an ORM in PHP with this latest article. It introduces the idea of dependency injection into the mix, showing how it can be used in the relationships between entities.

if you've already read the two installments that precede this one, it's probable that you’re familiar with the inner workings of this sample ORM. In those chapters I implemented the ORM's data access and mapping layers, along with a simple domain model. To be frank, the development of this last tier is entirely optional; however, it's useful for demonstrating the ORM's actual functionality in the deployment of a blog program, which naturally will handle some "typical" domain objects, namely blog entries, comments and authors.

They share the code for creating proxy objects and, using a "poor man's dependency injection container" made from a factory method, interfaces and service classes to handle the results.