day 05

Spring Boot JPA

• JPA is not a framework. It defines a concept that can be implemented by any framework.
• Spring Boot JPA is a Java specification for managing relational data in Java applications. It allows us to access and persist data between Java object/ class and relational database. JPA follows Object-Relation Mapping (ORM). It is a set of interfaces. It also provides a runtime EntityManager API for processing queries and transactions on the objects against the database. It uses a platform-independent object-oriented query language JPQL (Java Persistent Query Language).
• Features
  - It is a powerful repository and custom object-mapping abstraction.
  - It supports for cross-store persistence. It means an entity can be partially stored in MySQL and Neo4j (Graph Database Management System).
  - It dynamically generates queries from queries methods name.
  - The domain base classes provide basic properties.
  - It supports transparent auditing.
  - Possibility to integrate custom repository code.
  - It is easy to integrate with Spring Framework with the custom namespace.
• JPA annotations
  - @Repository
  - @Entity
  - @Id
  - @GeneratedValue
  - @OneToMany
  - @ManyToOne
  - @Query

Pagination in JPA

      Pageable pageable = PageRequest.of(int pageNum, int size, (Sort sort));
      Page<T> pageT = xxService.findAllByxx(X xx, pageable);
      List<T> listT = xxService.findAllByxx(X xx, pageable);
      // Page<T> obtain some extra information about page object, sum of T objects etc.