Doctrine integration

THere's probably going to be a lot of collision that will have to be handled. I haven't ever used Doctrine, but from your example above it looks like Doctrine might need its own APPPATH? That would cause problems with the framework for sure. I would recommend looking into Composer integration for starters, as that will handle the autoloading. Also read up on namespaces and how CI4 is different than CI3 when it comes to loading and the super object (e.g. you can't use $this->doctrine):
https://codeigniter4.github.io/CodeIgnit...dules.html

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I guess I should add that I have a module to help with adding relationship loading to CI4. I'm not a fan of ORM but this might get at some of the eager/lazy loading and easy access that ORMs provide:
https://github.com/tattersoftware/codeig...-relations
Note that there's a major release in the works on branch develop, so the current stable release will differ some.