JPA is the abbreviation of Java Persistence API and an ORM specification officially proposed!

JPA specifications are all in the package path: javax persistence.* For example, @ Entity, @ Id and @ Transient are all in this path. These are also some conventional annotations of ORM commonly used in the market.

Spring Data JPA is a JPA framework developed by spring based on Hibernate. It can greatly simplify the writing method of JPA, and realize the access and operation of data almost without writing specific code. In addition to CRUD, it also includes some common functions such as paging and sorting.

pom. Adding dependencies to XML

<dependency>
  <groupId>org.springframework.boot</groupId>
  <artifactId>spring-boot-starter-data-jpa</artifactId>
</dependency>
<dependency>
  <groupId>mysql</groupId>
  <artifactId>mysql-connector-java</artifactId>
</dependency>

application.properties configuration

spring.datasource.url=jdbc:mysql://localhost:3306/rumenz_springboot
spring.datasource.username=root
spring.datasource.password=root1234
spring.datasource.driver-class-name=com.mysql.cj.jdbc.Driver

spring.jpa.hibernate.ddl-auto=update
spring.sql.init.mode=always
spring.sql.init.schema-locations=classpath:/ddl/user-book.sql
spring.sql.init.data-locations=classpath:/ddl/user-book-data.sql

spring. jpa. hibernate. Whether DDL auto updates the database according to the entity class has four attribute values

spring. sql. init. Whether mode uses SQL file to initialize the database has three values

• spring. sql. init. Schema locations specifies the SQL file for creating tables
• spring. sql. init. Data locations specifies the data SQL file

Create entity class

User.java
@Getter
@Setter
@Builder
@AllArgsConstructor
@Entity //jpa required
@DynamicInsert //Fill default
@DynamicUpdate //Fill default
@Table(name = "user") //jpa required
@NoArgsConstructor
public class User {
    @Id //jpa required
    @GeneratedValue(strategy = GenerationType.IDENTITY) //jpa required
    private Integer id;
    private String name;
    private String domain;
    @Column(name = "age",columnDefinition = "tinyint default 0")
    private Integer age;
}

@GeneratedValue(strategy = GenerationType.IDENTITY) has the following types

• TABLE: use a specific database TABLE to save the primary key.
• SEQUENCE: generate the primary key according to the SEQUENCE of the underlying database, provided that the database supports the SEQUENCE.
• IDENTITY: the primary key is automatically generated by the database (mainly automatic growth type)
• AUTO: the primary key is controlled by the program.

Create a repository

The data persistence layer is responsible for accessing the database. The methods declared here generally do not need to be implemented. SQL statements can be automatically generated as long as they comply with the specifications of Jpa.

package com.rumenz.lession15.controller.repository;

import com.rumenz.lession15.controller.entity.User;
import org.springframework.data.domain.Page;
import org.springframework.data.domain.Pageable;
import org.springframework.data.jpa.repository.JpaRepository;
import org.springframework.data.repository.PagingAndSortingRepository;
import org.springframework.stereotype.Repository;

import java.util.List;
import java.util.Optional;

/**
 * @className: UserRepository
 * @description: TODO Class description
 * @author: Entry station rumenz com
 * @date: 2021/12/14
 **/

@Repository
public interface UserRepository extends PagingAndSortingRepository<User,Integer> {


    Optional<User> findById(Integer id);
    List<User> findDistinctUserByName(String name);
    Integer countUserByName(String name);
    List<User> readDistinctByName(String name);

    Page<User> findAllByName(String name, Pageable pageable);
}

Jpa can generate corresponding sql statements through the interface name, such as find By，read... By，query... By，count... By, And get By . These methods can include other expressions, such as setting the Distinct flag on the query to be created. The first by is used as a separator to indicate the beginning of the condition. Then, various conditions of entity attributes are defined And connected with And Or. For example:

interface RumenzRepository extends JpaRepository<Rumenz, Long> {

  List<Rumenz> findByEmailAddressAndLastname(EmailAddress emailAddress, String lastname);

  // Enable the distinct flag for queries
  List<Rumenz> findDistinctPeopleByLastnameOrFirstname(String lastname, String firstname);
  List<Rumenz> findPeopleDistinctByLastnameOrFirstname(String lastname, String firstname);

  // Enable ignore case for individual attributes
  List<Rumenz> findByLastnameIgnoreCase(String lastname);
  // Enable ignore case for all attributes
  List<Rumenz> findByLastnameAndFirstnameAllIgnoreCase(String lastname, String firstname);

  // Enable static Order by for queries
  List<Rumenz> findByLastnameOrderByFirstnameAsc(String lastname);
  List<Rumenz> findByLastnameOrderByFirstnameDesc(String lastname);
}

Give some examples

There are three types of repositories

JpaRepository inherits pagingandsortingreposition, and pagingandsortingreposition inherits CrudRepository.

• CrudRepository provides CRUD functions
• Pagingandsorting repository provides paging and sorting capabilities
• JPA repository provides JPA related methods, such as refreshing persistent data, batch deletion, etc.

service

The business logic layer is responsible for calling the Repository to process data and complete the business.

package com.rumenz.lession15.controller.service;

import com.rumenz.lession15.controller.entity.User;
import org.springframework.data.domain.Page;

import java.util.List;

/**
 * @className: UserService
 * @description: TODO Class description
 * @author: Entry station rumenz com
 * @date: 2021/12/14
 **/
public interface UserService {
    Integer save(User user);

    User get(Integer id);

    List<User> listByName(String name);

    Integer countByName(String name);

    List<User> readDistinctByName(String name);

    Page<User> listByNamePage(String name, Integer page, Integer pageSize);
}


//Implementation class


package com.rumenz.lession15.controller.service.lmpl;

import com.rumenz.lession15.controller.entity.User;

import com.rumenz.lession15.controller.repository.UserRepository;
import com.rumenz.lession15.controller.service.UserService;
import org.springframework.beans.factory.annotation.Autowired;

import org.springframework.data.domain.Page;
import org.springframework.data.domain.PageRequest;
import org.springframework.data.domain.Pageable;
import org.springframework.data.domain.Sort;
import org.springframework.stereotype.Service;

import java.util.List;
import java.util.Optional;

/**
 * @className: UserServiceImpl
 * @description: TODO Class description
 * @author: Entry station rumenz com
 * @date: 2021/12/14
 **/
@Service
public class UserServiceImpl implements UserService {

    @Autowired
    UserRepository userRepository;


    @Override
    public Integer save(User user) {
        User save = userRepository.save(user);
        return save.getId();
    }

    @Override
    public User get(Integer id) {
        Optional<User> opt = userRepository.findById(id);

        return opt.isPresent()?opt.get():null;
    }

    @Override
    public List<User> listByName(String name) {
        List<User> res = userRepository.findDistinctUserByName(name);
        return res;
    }

    @Override
    public Integer countByName(String name) {
        return userRepository.countUserByName(name);
    }

    @Override
    public List<User> readDistinctByName(String name) {

        return userRepository.readDistinctByName(name);
    }

    @Override
    public Page<User> listByNamePage(String name, Integer page, Integer pageSize) {

        Sort sort = Sort.by("id").descending();
        Pageable pageable= PageRequest.of(page-1, pageSize, sort);
        Page<User> res = userRepository.findAllByName(name, pageable);
        return res;
    }
}

Controller

The front-end controller is responsible for receiving the front-end request, calling service and returning data.

package com.rumenz.lession15.controller;

import com.rumenz.lession15.controller.entity.User;
import com.rumenz.lession15.controller.service.UserService;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.data.domain.Page;
import org.springframework.data.domain.Pageable;
import org.springframework.web.bind.annotation.GetMapping;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.RequestParam;
import org.springframework.web.bind.annotation.RestController;

import java.util.List;

/**
 * @className: RumenzController
 * @description: TODO Class description
 * @author: Entry station rumenz com
 * @date: 2021/12/14
 **/
@RestController
@RequestMapping("/rumenz")
public class RumenzController {

    @Autowired
    UserService userService;

    //Save data
    //If the data with id=1 does not exist, add it
    //If the data with id=1 exists, it will be updated
    @RequestMapping("/save")
    public String save(){
        User user=User.builder().id(1).name("Entry station 123").domain("https://rumenz.com").build();
        Integer save = userService.save(user);
        return save.toString();
    }
    //Query data by id
    @GetMapping("/get")
    public User get(@RequestParam("id") Integer id){
        return userService.get(id);
    }


    //Band query condition
    @GetMapping("/listByName")
    public List<User> get(@RequestParam("name") String name){
        return userService.listByName(name);
    }

    //Query qualified quantity by criteria
    @GetMapping("/countByName")
    public Integer countByName(@RequestParam("name") String name){
        return userService.countByName(name);
    }

    //Band query condition
    @GetMapping("/readDistinctByName")
    public List<User> readDistinctByName(@RequestParam("name") String name){
        return userService.readDistinctByName(name);
    }

    //Paging query
    //Band query condition
    @GetMapping("/listByNamePage")
    public Page<User> listByNamePage(@RequestParam("name") String name, @RequestParam("page") Integer page, @RequestParam("pageSize") Integer pageSize){
        return userService.listByNamePage(name,page,pageSize);
    }

}

Source code address of this summary:

• GitHub:https://github.com/mifunc/springboot/tree/main/lession15
• Gitee:https://gitee.com/rumenz/springboot/tree/master/lession15
• https://rumenz.com/rumenbiji/springboot-jpa-base.html