具有JoinTable關系的ManyToOne無法正常作業

解釋為什么會出現奇怪的行為并給出解決方案。

我有一個部門物體，一個部門最多可以有一個地址，一個地址也是一個物體，可以在多個部門之間共享。

為了在休眠中練習多對一關系，我決定有一個 JoinTable，這是我的物體定義：

import lombok.Getter;
import lombok.Setter;

import javax.persistence.*;

@Getter
@Setter
@Entity(name = "Address")
public class Address {
    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    private Long id;

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

地址物體：

@Getter
@Setter
@Entity(name = "department")
public class Department {

    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    private Long id;

    private String name;

    @ManyToOne
    @JoinColumn(name = "person_id")
    private Person manager;


    // many departments can have the same address
    // one department should have at most one address
    // todo not working as expected, we are not fetching the address of the department
    @ManyToOne(fetch = FetchType.EAGER)
    @JoinTable(name = "department_address",
            joinColumns = @JoinColumn(name = "address_id", referencedColumnName = "id"),
            inverseJoinColumns = @JoinColumn(name = "department_id", referencedColumnName = "id"))
    private Address address;
}

Person 物體（只是為了示例的完整性而添加）：

@Getter
@Setter
@Entity(name = "person")
public class Person {

    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    private Long id;

    private String name;

    @OneToOne(cascade = CascadeType.ALL)
    @JoinColumn(name = "address_id")
    private Address address;
}

當使用 spring data jpa 從資料庫中檢索部門時，就像我們沒有獲取與部門關聯的地址資料一樣。

這是資料庫的內容：

表部

表地址

表部門地址

存盤庫定義：

public interface DepartmentRepository extends JpaRepository<Department, Long> {}

在查找給定部門時，以我為例，它是部門 23，部門/23：

Department department = departmentRepository.findById(id).get();
Address address = department.getAddress();
System.out.println("address = "   address);

地址始終為空，即使對于部門 23，在表 department_address 中有一行，這里是部門的輸出

System.out.println("department = "   department);
department = Department(id=23, name=IT, manager=Person(id=3, name=hamida, address=Address(id=3, city=kharajiv)), address=null)

這是列印的 sql 查詢：

Hibernate: select department0_.id as id1_1_0_, department0_.person_id as person_i3_1_0_, department0_.name as name2_1_0_, department0_1_.department_id as departme1_2_0_, person1_.id as id1_3_1_, person1_.address_id as address_3_3_1_, person1_.name as name2_3_1_, address2_.id as id1_0_2_, address2_.name as name2_0_2_, address3_.id as id1_0_3_, address3_.name as name2_0_3_ from department department0_ left outer join department_address department0_1_ on department0_.id=department0_1_.address_id left outer join person person1_ on department0_.person_id=person1_.id left outer join Address address2_ on person1_.address_id=address2_.id left outer join Address address3_ on department0_1_.department_id=address3_.id where department0_.id=?

uj5u.com熱心網友回復：

左外連接地址 address3_ on department0_1_.department_id=address3_.id whe

也許我看錯了，但部門 ID 和地址 ID 不匹配。它必須是 deparment0_1.address_id = address3_.id

您可以嘗試將 inversecolumn 更改為 address_id

joinColumns = @JoinColumn(name = "deparment_id", referencedColumnName = "id"),
            inverseJoinColumns = @JoinColumn(name = "address_id", referencedColumnName = "id"))
    private Address address

uj5u.com熱心網友回復：

@JoinTable 注解用于指定多對多表關系的映射。在這種情況下使用 @ManyToMany

uj5u.com熱心網友回復：

joinColumns：分配與物體（在您的情況下為部門）本身相關的第三個表的列。inverseJoinColumns：分配與關聯物體相關的第三個表的列（在您的情況下為地址）。

你的是倒置的。您在 inverseJoinColumns 中有擁有物體（部門），在 joinColumns 中有地址

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標籤：爪哇 休眠 弹簧数据-jpa

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