Transaction Boundaries A transaction boundary is the point where a transaction starts and where it ends. In Spring, boundaries are defined by @Transactional on service methods. HTTP Request └── Controller (no transaction) └── @Transactional Service method ← transaction OPENS here ├── Repository call 1 ├── Repository call 2 └── method returns ← transaction COMMITS here Everything inside the @Transactional method runs in the same database transaction. The persistence context (first-level cache) lives for the duration of that transaction.

Most Spring Boot applications need to read and write data to a relational database. Spring Data JPA makes this dramatically simpler by generating the boilerplate data access code for you. This article explains what it is, how it fits together, and how to get started. The Stack: JPA, Hibernate, and Spring Data JPA These three things work together — understanding the layering matters: Your Code (Repository interfaces, @Entity classes) │ ▼ Spring Data JPA (generates repository implementations, adds convenience methods) │ ▼ JPA (Jakarta Persistence API) (standard specification: @Entity, @Id, EntityManager, JPQL) │ ▼ Hibernate (JPA implementation) (translates JPA operations to SQL, manages sessions) │ ▼ JDBC (Java Database Connectivity) (sends SQL to the database) │ ▼ PostgreSQL / MySQL / H2 / etc.