Spring Data JPA

JPA

• Java Persistence API
  • JPA is a Java specification that provides an ORM (Object-Relational-Mapping) framework to manage data in Java application
  • The common interface for different providers like Hibernate, ExlipseLink, etc.
• JPA architecture
  • 
    jpa_architecture

Spring Data JPA

• Spring Data JPA is built as an abstract layer over the JPA

• It has all features of JPA plus the Spring ease of development

• JPA vs. Spring Data JPA

• For years, developers have written boilerplate code to create a JPA DAO for basic functionalities. Spring helps to significantly reduce this amount of code by providing minimal interfaces and actual implementations

• Spring Data JPA uses Hibernate under the hood

• How to use Spring Data JPA?

  1. Config database in application.properties

     • spring.datasource.url=jdbc:postgresql://localhost:5432/jobApp
       spring.datasource.username=postgres
       spring.datasource.password=****
       spring.datasource.driver-class-name=org.postgresql.Driver
       
       spring.jpa.hibernate.ddl-auto=update
       spring.jpa.show-sql=true

  2. Define an entity

     • package com.hadjshell.JobAd.model;
       
       import jakarta.persistence.Entity;
       import jakarta.persistence.Id;
       import org.springframework.context.annotation.Scope;
       import org.springframework.stereotype.Component;
       
       @Component
       @Scope("prototype")
       @Entity
       @Table(name = "jobPost")
       public class JobPost implements Serializable {
       
           @Id		// primary key
         	// Indicate that ID should be generated automatically
         	@GeneratedValue(strategy=GenerationType.AUTO)
           private int postId;
           private String postProfile;
           private String postDesc;
         	@Column(nullable = false)
           private int reqExperience;
           private List<String> postTechStack;
       
           public JobPost(int postId, String postProfile, String postDesc, int reqExperience, List<String> postTechStack) {
               this.postId = postId;
               this.postProfile = postProfile;
               this.postDesc = postDesc;
               this.reqExperience = reqExperience;
               this.postTechStack = postTechStack;
           }
       
           protected JobPost() {
           }
       
       		// getter and setter
       }

  3. Build repository layer and create queries

     • package com.hadjshell.JobAd.repo;
       
       import com.hadjshell.JobAd.model.JobPost;
       import org.springframework.data.jpa.repository.JpaRepository;
       import org.springframework.data.jpa.repository.Query;
       import org.springframework.stereotype.Repository;
       
       import java.util.List;
       
       @Repository
       // Specify the stored object's type and its pk's type
       public interface JobRepo extends JpaRepository<JobPost, Integer> {
       
           @Query("SELECT j FROM JobPost j WHERE j.reqExperience >= :year")
           List<JobPost> findByReqExperienceGreaterOrEqualThan(@Param("year") int year);
       
         	List<JobPost> findByPostProfileContaining(String keyword);
       }

     • Spring Data JPA uses JPA to store data in a relational database

     • It is able to create repository implementations automatically, at runtime, from a repository interface

     • Spring Data JPA creates a bunch of findBy_ methods for you behind the scene when you specify them in the @Repository without specifying @Query

     • findById returns an Optional object

  4. Build service layer and controller layer