In almost every modern Java textbook, data persistence is introduced with a dangerous shortcut. You are told to create an interface, extend JpaRepository<Product, UUID> , and call it a day. The result? Without even noticing, you have tightly coupled your entire application to Spring Data and Hibernate. The moment a junior developer leaks Pageable or Specification from Spring into your clean @Service layer, or worse—directly into your REST controllers (as we discussed in Chapte...