java - 可嵌入对象未持久保存到辅助表中

Question

在我的真实项目中，有一个具有约 15 个属性(列)的实体。我需要存储大约 10 个与实体相关的属性。为了避免在同一个表中创建新列，一种方法是将新属性存储在另一个实体中，并通过一对一关系将它们链接起来。 Here我找到了另一种方法，这意味着将可嵌入对象存储在辅助表中。问题在于，具有未初始化属性的可嵌入对象不会持久化到数据库中。我已在 demo project 中重现了该问题:

@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

<小时/>

@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

<小时/>

@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;
    }

}

<小时/>

@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);
    }
}

<小时/>

POST localhost:8080/student/nonEmptyAddress 返回预期输出:

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)

<小时/>

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

<小时/>

GET localhost:8080/student/4 返回上面的结果。现在让我们创建一个带有 Address 对象的学生，其中所有属性均未初始化:

POST localhost:8080/student/nonEmptyAddress 返回预期输出:

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)

<小时/>

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

但是，当我调用 GET 端点时，我收到另一个结果。获取本地主机:8080/student/5:

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

<小时/>

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

<小时/>

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，但地址为空。当 Address 对象中至少有一个初始化属性时，用地址更新学生可以按预期进行。但是，如果您使用所有属性都为空的地址更新学生 (PUT localhost:8080/student/3/emptyAddress)，则表 ADDRESSES 甚至不会被更新。

上面的例子有什么问题吗？我认为使用 @Embeddable 和 @Secondary 表来达到预期结果不是正确的方法。

Answer 1

在将类实现为 @Embeddable 时，Hibernate 会在该表上创建一个左外连接，仅选择四个可为空的字段。因为这些值为 null，所以不会返回任何内容，并且对象也为 null(尽管它们是表中的记录)。

尝试在Address表中使用@Column添加字段的外键映射。由于此列始终被填充，因此尽管所有字段都为空，查询仍会选取整行并正确构造对象。