Help to apply onion architecture in codeIgniter

For dep injection, you should be able to do, more or less on both 3 and 4:
CI3 - https://forum.codeigniter.com/post-334318.html
CI4 (old article, but presumably it hasn't changed that much) - http://blog.newmythmedia.com/blog/show/2...eIgniter_4

For CI4 it'll be available for core level (aka DB and what not).

If you already have Java MVC experience, it might make it easier, because you already know the principles, or harder, because essentially PHP and Java work completely different to each other.

Effectively it's all about what code you put in models and what code you put in controllers, no?