How to use JPA as a data persistence framework in SpringBoot

JPA is the abbreviation of Java Persistence API. The Chinese name is Java Persistence Layer API. It is a mapping relationship between JDK 5.0 annotations or XML description objects and relational tables, and persists entity objects at runtime into the database.

1. Introduction of dependencies

<!-- spring mvc -->
<dependency>
    <groupId>org.springframework.boot</groupId>
    <artifactId>spring-boot-starter-web</artifactId>
</dependency>

<!-- mysql 驱动 -->
<dependency>
    <groupId>mysql</groupId>
    <artifactId>mysql-connector-java</artifactId>
    <scope>runtime</scope>
</dependency>

<!-- lombok -->
<dependency>
    <groupId>org.projectlombok</groupId>
    <artifactId>lombok</artifactId>
</dependency>

<!-- jpa持久层 -->
<dependency>
    <groupId>org.springframework.boot</groupId>
    <artifactId>spring-boot-starter-data-jpa</artifactId>
</dependency>

2. Database connection configuration

server:
  port: 8080

spring:
  datasource:
    url: jdbc:mysql://127.0.0.1:3306/jpa-demo?useUnicode=true&useJDBCCompliantTimezoneShift=true&useLegacyDatetimeCode=false&serverTimezone=Asia/Shanghai&useSSL=true&characterEncoding=UTF-8
    driver-class-name: com.mysql.cj.jdbc.Driver
    username: root
    password: 123456
  jpa:
    hibernate:
      # 自动创建表
      ddl-auto: update

ddl-auto has a total of five optional values

• none: Do nothing

• create: Each time hibernate is loaded, the last generated table will be deleted, and then a new table will be generated based on your model class, even if it is twice This is performed even if there are no changes. This is an important reason for the loss of database table data.

• create-drop: The table is generated based on the model class every time hibernate is loaded, but the table is automatically deleted as soon as sessionFactory is closed.

• update: The most commonly used attribute. When hibernate is loaded for the first time, the table structure will be automatically established based on the model class (provided that the database is established first). When hibernate is loaded later, it will be based on the model class. The class automatically updates the table structure. Even if the table structure changes but the rows in the table still exist, the previous rows will not be deleted. It should be noted that when deployed to the server, the table structure will not be established immediately, but will wait until the application is run for the first time.

• validate: Each time hibernate is loaded, the created database table structure is verified. It will only be compared with the table in the database, and no new table will be created, but new values ​​will be inserted.

3. Data object (DO)

import lombok.Data;

import javax.persistence.*;

@Table(name = "sys_user")
@Entity
@Data
public class SysUserDO {

    /**
     * 主键-自增
     */
    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    private Long id;

    @Column(columnDefinition = "varchar(12) comment '用户名称'")
    private String name;

    @Column(columnDefinition = "varchar(50) comment '邮箱'")
    private String email;
}

• @Id, indicating that this attribute is the primary key field

• @GeneratedValue(strategy = GenerationType.IDENTITY), using the primary key auto-increment method

• @Column, specifies the attributes of the database field, you can set the data type, length, comments and other information , you can also just write an annotation, jpa will automatically identify

4. Persistence object

import com.biz.jpa.entity.SysUserDO;
import org.springframework.data.jpa.repository.JpaRepository;
import org.springframework.stereotype.Repository;

@Repository
public interface SysUserRepository extends JpaRepository<SysUserDO, Long> {
}

@Repository, indicating that this is the data access layer

5. Business layer

import com.biz.jpa.dao.SysUserRepository;
import com.biz.jpa.entity.SysUserDO;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.stereotype.Service;

@Service
public class SysUserService {

    @Autowired
    private SysUserRepository sysUserRepository;

    public SysUserDO saveUser() {
        SysUserDO sysUser = new SysUserDO();
        sysUser.setName("Asurplus");
        sysUser.setEmail("123456@qq.com");
        sysUserRepository.save(sysUser);
        return sysUser;
    }
}

We insert a piece of data into the sys_user table. Since the primary key is automatically incremented, we do not need to set the primary key. After the insertion is successful, the auto-incremented primary key will be automatically written back to the object

6. Test

import com.biz.jpa.entity.SysUserDO;
import com.biz.jpa.service.SysUserService;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.web.bind.annotation.GetMapping;
import org.springframework.web.bind.annotation.RestController;

@RestController
public class SysUserController {

    @Autowired
    private SysUserService sysUserService;

    @GetMapping("save")
    public SysUserDO save() {
        return sysUserService.saveUser();
    }
}

Access:

http://localhost:8080/save

Return:

{"id":1,"name":"Asurplus","email":"123456@qq.com"}

The insertion is successful and the auto-incremented primary key is returned. The integration of Jpa is completed here. More usage of Jpa needs to be explored in actual project development.

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