Java Persistence API (JPA)

What

• An API specification (ie hibernate is written to)

• https://en.wikipedia.org/wiki/Java_Persistence_API

• A persistence entity is a lightweight Java class whose state is typically persisted to a table in a relational database

• Use of POJOs as entities

  • The pojos will need a zero arg constructor to work

  • It will need an id, which is for the jpa to interact with the database

• Handles all the JDBC and sql implementations

• https://vladmihalcea.com/best-spring-data-jparepository/

Advantages

• https://www.sitepoint.com/5-reasons-to-use-jpa-hibernate/

Negatives

• Add one more thing you have to worry about (if you have a complex database interactions).

• JPA Have limitations, that is the reason for have a Native interface, you can send Native SQL sentences to database soooooo, you can survive without JPA or any ORM.

• It’s heavyweight, it creates a complete environment that you almost never need.

• Forces domain objects to hold database specific knowledge

Linkage

• Need to override Equals and Hashcode, due to id field in entity

  • We will use the id to determine the object equality

Mappings

• Linking entity pojos, with each other in code which will be mimicd in the database ie parent child many to many

Patterns

• https://vladmihalcea.com/spring-data-findall-anti-pattern/

  • you should not really offer your clients a way to fetch an entire database table

  • define a new base interface by extending the Repository interface instead of the JpaRepository and declaring explicitly which methods are allowed to be inherited by your custom repositories

  public interface BaseJpaRepository<T, ID> extends Repository<T, ID> {
  
    Optional<T> findById(ID id);
  
    T getReferenceById(ID id);
     
    boolean existsById(ID id);
     
    void deleteById(ID id);
  
    void delete(T entity);
     
    long count(); 
  } 

  • the entities that have a large number of records can now define their specific Repository interface by extending the BaseJpaRepository

  • the entities with a small number of records can extend the default Spring Data JpaRepository

Links

• https://www.youtube.com/watch?v=mcl_nibV39s The ULTIMATE Guide for Spring Data JPA & Hibernate | 5 Hours Tutorial

• https://www.youtube.com/watch?v=exqfB1WaqIw Performance oriented Spring Data JPA & Hibernate by Maciej Walkowiak

  • https://github.com/Kehrlann/spring-security-the-good-parts

• https://www.youtube.com/watch?v=iJ2muJniikY Spring Security, demystified by Daniel Garnier Moiroux