PHP OOP core framework

Solution 1:

The original question

The first part, about the URLs is something called: Routing or Dispatching. There is quite good article about it in relationship with Symfony 2.x, but the the idea behind it is what matters. Also, you might looks at ways how other frameworks implement it.

As for your original URL examples, galleries will be stored in DB. Won't they? And they will have a unique ID. Which makes this, /backend/projects/edit/5/gallery/2 quite pointless. Instead your URL should look more like:

/backend/gallery/5/edit         // edit gallery with ID 5
/backend/project/3              // view project with ID 3
/backend/galleries/project/4    // list galleries filtered by project with ID 4

The URL should contain only the information you really need.

This also would indicate 3 controllers:

single gallery management
single project management
dealing with lists of galleries

And the example URLs would have pattern similar to this:

/backend(/:controller(/:id|:page)(/:action(/:parameter)))

Where the /backend part is mandatory, but the controller is optional. If controller is found , then id ( or page, when you deal with lists ) and action is optional. If action is found, additional parameter is optional. This structure would let you deal with majority of your routes, if written as a regular expression.

OOP beyond classes

Before you start in on using or writing some sort of PHP framework, you should learn how to write proper object oriented code. And that does not mean "know how to write a class". It means, that you have to actually understand, what is object oriented programming, what principles it is based on, what common mistakes people make and what are the most prevalent misconceptions. Here are few lecture that might help you with it:

Inheritance, Polymorphism, & Testing
Advanced OO Patterns ^(slides)
Unit Testing
The Principles of Agile Design
Global State and Singletons
Don't Look For Things!
Beyond Frameworks ^(slide)
Agility and Quality ^(slides)
Clean Code I: Arguments
Clean Code III: Functions

This should give you some overview of the subject .. yeah, its a lot. But is suspect that you will prefer videos over books. Otherwise, some reading materials:

PHP Object-Oriented Solutions
Design Patterns Explained
Patterns of Enterprise Application Architecture

You will notice that a lot of materials are language-agnostic. That's because the theory, for class-based object oriented languages, is the same.

P.S.

Be careful with extends keyword in your code. It means "is a". It is OK, if class Oak extends Tree, because all oaks are trees. But if you have class User extends Database, someone might get offended. There is actually an OOP principle which talks about it: Liskov substitution principle .. also there is a very short explanation

Solution 2:

If this project has images, where should I load the image class to handle those? Should I load it in the project_model like $this->images = new Images(); and have a function inside the model

Yes. The goal of the model is to encapsulate business logic so that you only need to write the algorithms once, and share them multiple times. What I would do if I were you is to add a getImages() method to the Project model as the images are a direct attribute to a project, this makes it so that each project knows how to retrieve it's own images.

Your code is missing a few key concepts compared to ORMS I have worked with (hydration and peer/table) classes, so I will try to stick with your code. You can retrieve the images through the Project object, then reference the images via the view 1 of 2 ways:

// Controller
$this->project = new Project();
$this->projectImages = $project->getImages(); // Implemenation #2

// View

// Implemenation #1 (reference to object initialized in controller)
<?php foreach ($project->getImages() as $image): ?>
<img src="<?php echo $image['path'] ?>" />
<?php endforeach ?>

// Implemenation #2 (reference to separate variable initialized in controller)
<?php foreach ($projectImages as $image): ?>
<img src="<?php echo $image['path'] ?>" />
<?php endforeach ?>

Above is demonstrative only, but should give you an idea. I would suggest that you take a look at Doctrine. It is a proven and stable ORM which provides much of what you are attempting to write, plus it adds the missing components that I mentioned earlier; hydration, object relations, and Table classes, along with many other features such as nested sets.