JPA中的@Embedded和@Embeddable注释的使用

JPA中的@Embedded和@Embeddable注释

概念很枯燥, 通过代码理解吧

模拟场景

1.建表,插入一条数据

create table if not exists `User`(
    `id` int(4) auto_increment  not null,
    `name` varchar(8) not null,
    `city` varchar(12) not null,
    `district` varchar(12) not null,
    `street` varchar(12) not null,
    primary key(`id`)
)engine=innodb default charset=utf8;

insert into user values(1, 'Joshua', '男', 1.75, '重庆', '璧山区', 'XX街道', 'XXX小区');

2.建立对应 实体类 以及 repository接口

User类

@Entity
@Table(catalog = "jpa", name = "user")
public class User {

    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    @Column(name = "id")
    private Integer id;

    @Column(name = "name")
    private String name;

    @Column(name = "sex")
    private String sex;

    @Column(name = "height")
    private Float height;

    @Column(name = "city")
    private String city;

    @Column(name = "district")
    private String district;

    @Column(name = "street")
    private String street;

    @Column(name = "community")
    private String community;
}

UserRepository接口

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

进行环境搭建测试

@SpringBootTest
class DemoSpringApplicationTests {

    @Autowired
    private UserRepository userRepository;

    @Test
    void test01() {
        userRepository.findById(1).ifPresent(System.out::println);
        // 输出结果 => User(id=1, name=Joshua, sex=男, height=1.75, city=重庆, district=璧山区, street=XX街道, community=XXX小区)
    }
}

至此,一个简单的环境搭建成功了

那么问题来了, User类字段过多,是不是可以整合一下 ?

比如 city 、district 、street 、community这些字段，我们都可以整合为一个 Address 类,并通过@Embedded和@Embeddable注解进行关联

Address 类

@Builder
@Data
@AllArgsConstructor
@NoArgsConstructor
//以上四个注解用于构造对象,以及get/set/toString...
@Embeddable // 声明该类是可嵌入的
public class Address {

    /*
    属性名有些问题需要注意下:
    1. 尽量和数据库字段一样
    2. 如果属性名和数据库字段名不一样,加上@Column(name = "数据库字段名")
    3. 拓展: 如果Address类不仅被 User 引用,其他类也在使用,说明这些表结构类似,但是字段名在每个表不一样,可以去了解一下@AttributeOverrides注解
    */
    private String city;
    private String district;
    private String street;
    private String community;
}

改造后的 User 类

@Builder
@Data
@AllArgsConstructor
@NoArgsConstructor
@Entity
@Table(catalog = "jpa", name = "user")
public class User {

    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    @Column(name = "id")
    private Integer id;

    @Column(name = "name")
    private String name;

    @Column(name = "sex")
    private String sex;

    @Column(name = "height")
    private Float height;

    @Embedded // 其实通过测试发现,这个注解在Address使用了@Embeddable后可省略,但是防止后面出问题还是加上
    private Address address;

}

进行测试

@SpringBootTest
class DemoSpringApplicationTests {

    @Autowired
    private UserRepository userRepository;

    @Test
    void test02() {
        Address address = Address.builder()
                .city("重庆").district("合川区").street("YY街道").community("YYY小区").build();
        User user = User.builder()
       		   .id(2).name("Jack").height(1.8f).sex("男").address(address).build();
        User save = userRepository.save(user);
        System.out.println(save);
       // 输出结果 => User(id=8, name=Jack, sex=男, height=1.8, address=Address(city=重庆, district=合川区, street=YY街道, community=YYY小区))
    }
}

查看数据库发现, 这条数据成功插入