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 Chapter 1)—your clean architecture is officially dead. Your core module now depends on the database infrastructure framework.
If tomorrow you want to switch a high-throughput read-heavy path to raw JDBC, or migrate a specific sub-domain to MongoDB, you will realize your business logic is trapped in a framework prison.
In Chapter 3 of our Evolutionary Architecture series, we are building the Dao API Module. A zero-dependency, pure Java module that strictly defines the contracts for persistence and querying, without knowing a single thing about SQL, Hibernate, or Spring.
