JPA

• The Java Persistence API (JPA) is a specification that defines how to persist data in Java applications.
• The primary focus of JPA is the ORM layer.
• ref: https://www.baeldung.com/learn-jpa-hibernate

JPA implementations/providers

• Hibernate
• EclipseLink
• Apache OpenJPA
• TopLink
• JDO

Spring Data JPA

• https://docs.spring.io/spring-data/jpa/reference/

Hibernate

• https://docs.jboss.org/hibernate/orm/6.1/userguide/html_single/Hibernate_User_Guide.html

Spring Data JPA and Hibernate

• With Hibernate you get:
  • declarative transaction management using JPA/Hibernate transactions
  • exception translation
  • the JPA EntityManager or the Hibernate SessionFactory as injectable beans
• With Spring Data JPA, you get the above plus:
  • interface-only repositories, using method names to infer queries automatically
  • @Query annotation to define the query that an interface method should return
  • automatic handling of Pageable queries
  • base classes for standard crud repositories
• Spring Data JPA adds an extra layer of abstraction on the top of our JPA provider like Hibernate

Libraries

• org.springframework.boot:spring-boot-starter-data-jpa
  • It includes spring data, hibernate, HikariCP, JPA API, JPA Implementation (default is hibernate), JDBC and other required libraries.
• com.h2database:h2 (for H2 database)
• mysql:mysql-connector-java (for MySQL)
• org.springframework.boot:spring-boot-starter-data-mongodb (MongoDB)

More to discover

• EntityManager and SessionFactory
• Entity vs Table
• JPQL
• Native Query
• Parametrized Query
• Pagination

Transactions

• https://stackoverflow.com/questions/1099025/spring-transactional-what-happens-in-background

Object–relational impedance mismatch

• Set of difficulties going between data in relational data stores and data in domain-driven object models.