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Lesson 6 - Passing dependencies with Dependency Injection

In the previous lesson, Wrong ways of passing dependencies - Singleton and SL, we completed a walk through the wrong ways of passing dependencies in multi-tier applications. Overall, it was about using any static class members, including Singleton, but also about passing dependencies through a container, known as the Service Locator pattern, or different variations of these approaches. Today, we're gonna show how to do it right on our car example as always.

Laborious ways

So far, the only right way we know is to pass dependencies manually one by one. This is also the approach we showed at the very beginning of the course. We created a database instance in index.php and passed it to the controller and through the controller to the model where it was needed. Although this approach is correct from the software-design point of view, you can certainly imagine how much work it would take to pass several dependencies like this even in a medium-sized application. And since controllers are created automatically by the router, we 'd also need to identify which dependencies should be passed to which controller. Last time, I promised I would stop bothering you with the wrong solutions and questions any more. Today's lessons will bring answers to everything. Really :)

What was wrong?

In all the presented solutions, we tried to hack the code so we didn't have to pass dependencies. This CANNOT be achieved without negative impacts. All such attempts will always result in failures. If we don't pass


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Article description

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This tutorial explains what we did wrong till now, what Inversion of Control is and how the Dependency Injection pattern works in practice.

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Article has been written for you by David Capka
The author is a programmer, who likes web technologies and being the lead/chief article writer at He shares his knowledge with the community and is always looking to improve. He believes that anyone can do what they set their mind to.
Unicorn university David learned IT at the Unicorn University - a prestigious college providing education on IT and economics.