The Hibernate internals every Spring Boot developer must understand — SessionFactory vs Session thread safety, entity states, dirty checking, first-level cache, second-level cache, and LazyInitializationException.
A clear breakdown of how JPA, Hibernate, Spring Data, and Spring Data JPA relate to each other — the layer model every developer must understand before working with any of them.
What causes N+1 queries in JPA/Hibernate, how to diagnose them, and how to fix them with JOIN FETCH, @EntityGraph, DTO projections, and batch fetching.