I only studied spring data jpa.. When I was doing a project and there was a part I didn't know or was confused about, I would always look it up and it would always be like this...what the heck...what is that...what is that? It was hard because it was just concepts that I couldn't understand at all. The more I looked for it, the more I got stuck in the swamp instead of knowing anything. But this lecture is very helpful because it gives me the overall concept of the things I was looking for! Oh, I didn't know jpa was this profound and systematic..