springboot之JPA初识

说明：此处JPA之spring data jpa,springboot版本为2.1.3.RELEASE，springdata jpa版本为2.1.5.RELEASE
1、首先创建一个基本的springboot项目，添加mysql和JPA依赖，具体的pom.xml，如下：

    <dependencies>
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-data-jpa</artifactId>
        </dependency>
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-web</artifactId>
        </dependency>

        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-devtools</artifactId>
            <scope>runtime</scope>
        </dependency>
        <dependency>
            <groupId>mysql</groupId>
            <artifactId>mysql-connector-java</artifactId>
            <scope>runtime</scope>
        </dependency>
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-configuration-processor</artifactId>
            <optional>true</optional>
        </dependency>
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-test</artifactId>
            <scope>test</scope>
        </dependency>
    </dependencies>

2、添加配置，此处使用application.yml为配置文件，配置数据源及JPA信息如下：

spring:
  datasource:
    driver-class-name: com.mysql.cj.jdbc.Driver
    url: jdbc:mysql://127.0.0.1:3306/jpa?useUnicode=true&characterEncoding=utf-8&serverTimezone=UTC
    username: root
    password: 1234
  jpa:
    hibernate:
      ddl-auto: update
    show-sql: true
    properties:
      hibernate:
        format_sql: true

此处需要特别注意的是mysql驱动类为com.mysql.cj.jdbc.Driver
3、创建实体类

@Entity
@Table(name="d_demo")
public class Demo implements Serializable{

    private static final long serialVersionUID = 4676210938649473427L;
    
    @Id
    @GeneratedValue(strategy=GenerationType.IDENTITY)
    private Integer id;
    
    private String name;
    
    private Boolean flag;

    public Integer getId() {
        return id;
    }

    public void setId(Integer id) {
        this.id = id;
    }

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    public Boolean getFlag() {
        return flag;
    }

    public void setFlag(Boolean flag) {
        this.flag = flag;
    }

    @Override
    public String toString() {
        return "Demo [id=" + id + ", name=" + name + ", flag=" + flag + "]";
    }
}

简单说明：@Entity标注为实体，@Table标注表名，@Id主键，@GeneratedValue主键生成策略；如果字段名与实体名不一致，需要使用@Column。
数据表：

image.png

4、创建DAO

public interface DemoRepository extends JpaRepository<Demo, Integer>{

}

此处不需要使用@Repository
5、测试
此处为简单测试不再创建service
新建

    @Autowired
    private DemoRepository demoRepository;
    
    @Test
    public void testInsert() {
        Demo demo = new Demo();
        demo.setName("AA");
        demo.setFlag(true);
        demo = demoRepository.save(demo);
        System.out.println(demo);
    }

执行结果

image.png

查询

    @Test
    public void testSelect() {
        Demo demo = demoRepository.findById(26).get();
        System.out.println(demo);
    }

执行结果

image.png

findById返回对象为Optional，Optional为1.8新特性，需要再执行get()返回实体。
更新

    @Test
    public void testUpdate() {
        Demo demo = demoRepository.findById(26).get();
        demo.setName("AA-New");
        demoRepository.save(demo);
        System.out.println(demo);
    }

执行结果

image.png

删除

    @Test
    public void testDelete() {
        demoRepository.deleteById(26);
    }

执行结果

image.png