可嵌入的对象没有被持久化到辅助表上。

问题描述 投票：0回答：1

在我的真实项目中，有一个实体，有大约15个属性（列）。我需要再存储10个与该实体相关的属性。为了避免在同一个表中创建新的列，一种方法是将新的属性存储在另一个实体中，并用一对一的关系将它们连接起来。下面是 我发现了另一种方法，它意味着将一个可嵌入对象存储在一个辅助表中，问题是一个没有初始化属性的可嵌入对象不能持久化到数据库中。我已经将这个问题重现在 示范工程:

@Entity
@Table(name = "STUDENTS")
@SecondaryTable(
        name = ADDRESSES,
        pkJoinColumns = @PrimaryKeyJoinColumn(name = "STUDENT_ID")
)
public class Student {

    @Id
    @GeneratedValue
    private Long id;

    private String firstName;
    private String lastName;

    @Embedded // not needed
    private Address address;
    
    //constructors, getters and setters

@Embeddable
public class Address {

    public static final String ADDRESSES = "ADDRESSES";

    @Column(table = ADDRESSES)
    private String country;
    @Column(table = ADDRESSES)
    private String city;
    @Column(table = ADDRESSES)
    private String street;
    @Column(table = ADDRESSES)
    private Integer houseNumber;
    
    //constructors, getters and setters

@Service
@Transactional
public class StudentService {

    @Autowired
    private StudentRepository studentRepository;

    @Transactional(readOnly = true)
    public List<Student> findAll() {
        return studentRepository.findAll();
    }

    public Student createStudentWithEmptyAddress() {
        Student student = new Student("Caleb", "Baker", new Address());
        return studentRepository.save(student);
    }

    public Student createStudentWithNonEmptyAddress() {
        Address address = new Address("France", "Paris", "Rue Vieille Du Temple", 88);
        Student student = new Student("Cayden", "Hoover", address);
        return studentRepository.save(student);
    }

    public Student findById(Long id) {
        return studentRepository
                .findById(id)
                .orElseThrow(() -> new RuntimeException("Student with id: " + id + " was not found"));
    }

    public Student updateStudentWithEmptyAddress(Long id) {
        Student student = findById(id);
        student.setAddress(new Address());
        return student;
    }

    public Student updateStudentWithNonEmptyAddress(Long id) {
        Student student = findById(id);
        Address address = new Address("USA", "New York", "Stanton Street", 17);
        student.setAddress(address);
        return student;
    }

}

@RestController
@RequestMapping("/student")
public class StudentController {

    @Autowired
    private StudentService studentService;

    @GetMapping("/all")
    @ResponseStatus(OK)
    public List<Student> findAll() {
        return studentService.findAll();
    }

    @GetMapping("/{id}")
    @ResponseStatus(OK)
    public Student findOne(@PathVariable Long id) {
        return studentService.findById(id);
    }

    @PostMapping("/emptyAddress")
    @ResponseStatus(CREATED)
    public Student createStudentWithEmptyAddress() {
        return studentService.createStudentWithEmptyAddress();
    }

    @PostMapping("/nonEmptyAddress")
    @ResponseStatus(CREATED)
    public Student createStudentWithNonEmptyAddress() {
        return studentService.createStudentWithNonEmptyAddress();
    }

    @PutMapping("/{id}/emptyAddress")
    @ResponseStatus(OK)
    public Student updateStudentWithEmptyAddress(@PathVariable Long id) {
        return studentService.updateStudentWithEmptyAddress(id);
    }

    @PutMapping("/{id}/nonEmptyAddress")
    @ResponseStatus(OK)
    public Student updateStudentWithNonEmptyAddress(@PathVariable Long id) {
        return studentService.updateStudentWithNonEmptyAddress(id);
    }
}

POST localhost:8080studentnonEmptyAddress返回预期的输出。

jdbc.sqlonly: insert into students (first_name, last_name, id) values ('Cayden', 'Hoover', 4) 
jdbc.sqlonly: insert into addresses (city, country, house_number, street, student_id) values ('Paris', 'France', 88, 'Rue Vieille Du Temple', 4)

{
    "id": 4,
    "firstName": "Cayden",
    "lastName": "Hoover",
    "address": {
        "country": "France",
        "city": "Paris",
        "street": "Rue Vieille Du Temple",
        "houseNumber": 88
    }
}

GET localhost:8080student4 返回上述结果。现在让我们用一个Address对象创建一个学生，在这个对象中，所有的属性都没有初始化。

POST localhost:8080studentnonEmptyAddress 返回预期的输出。

jdbc.sqlonly: insert into students (first_name, last_name, id) values ('Caleb', 'Baker', 5)
jdbc.sqlonly: insert into addresses (city, country, house_number, street, student_id) values (NULL, NULL, NULL, NULL, 5)

{
    "id": 5,
    "firstName": "Caleb",
    "lastName": "Baker",
    "address": {
        "country": null,
        "city": null,
        "street": null,
        "houseNumber": null
    }
}

然而，当我调用GET端点时，我收到了另一个结果。GET localhost:8080student5 。

jdbc.sqlonly: select student0_.id as id1_1_0_, student0_.first_name as first_na2_1_0_, student0_.last_name as last_nam3_1_0_, student0_1_.city as city1_0_0_, student0_1_.country as country2_0_0_, student0_1_.house_number as house_nu3_0_0_, student0_1_.street as street4_0_0_ from students student0_ left outer join addresses student0_1_ on student0_.id=student0_1_.student_id where student0_.id=5

{
    "id": 5,
    "firstName": "Caleb",
    "lastName": "Baker",
    "address": null
}

Content of ADRESSES table:
    CITY    COUNTRY     HOUSE_NUMBER    STREET                     STUDENT_ID  
    Paris   France          88          Rue Vieille Du Temple           4
    null    null            null        null                            5

尽管ADRESSES表中存在第二条记录，但地址是空的.当地址对象中至少有一个初始化的属性时，用地址更新学生的工作与预期的一样。然而，如果你更新一个学生的地址，其中所有属性都是空的（PUT localhost:8080student3emptyAddress），那么ADRESSES表甚至没有被更新。

上面的例子有什么问题？我认为使用@Embeddable和@Secondary表来达到预期的效果是不对的。

java hibernate spring-boot jpa embeddable
1个回答
0
投票

当实现一个类为@Embeddable时，Hibernate在该表上创建了一个左外连接，只选择了四个可空字段。因为这些值是空的，所以什么也不返回，对象是空的（尽管它们是表中的一条记录）。

试着使用地址表中的@Column添加字段的外键映射。由于这一列总是被填充，所以尽管所有字段都是空的，查询还是会拾取整行并正确构造对象。

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