主页 / 问题 / 1404815
Accepted
Sergey Zh.
Asked:2022-06-29 01:51:43 +0000 UTC2022-06-29 01:51:43 +0000 UTC

使用多对多关系和 Spring Data JPA 时重复行

  • 772

有 Person 和 Address 实体，它们之间存在 ManyToMany 关系

但是当使用spring data jpa存储库保存时，由于某种原因，在persons_addresses表中所有关系字符串都保存了两次

问题是，为什么会发生这种情况，我做错了什么？

@Entity
@Table(name = "persons")
@Data
@NoArgsConstructor
public class Person {
    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    @Column(name = "id")
    private Long id;

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

    @ManyToMany(cascade = CascadeType.ALL)
    @JoinTable(name = "persons_addresses",
            joinColumns = @JoinColumn(name = "person_id"),
            inverseJoinColumns = @JoinColumn(name = "address_id"))
    private List<Address> addresses;
}



@Entity
@Table(name = "addresses")
@Data
@NoArgsConstructor
public class Address {
    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    @Column(name = "id")
    private Long id;

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

    @ManyToMany(cascade = CascadeType.ALL)
    @JoinTable(name = "persons_addresses",
            joinColumns = @JoinColumn(name = "address_id"),
            inverseJoinColumns = @JoinColumn(name = "person_id"))
    private List<Person> persons;
}

// 在事务中使用

@Transactional
public PersonDto create(PersonDto newPerson) {
    Person person = new Person();
    person.setFullName(newPerson.getFullName());

    person.setAddresses(new ArrayList<>());
    newPerson.getAddresses().forEach(a -> {
        Address address = addressRepository.findByAddressName(a);
        if (address == null) {
            address = new Address();
            address.setAddressName(a);
            address.setPersons(new ArrayList<>());
        }
        address.getPersons().add(person);
        addressRepository.save(address);
        person.getAddresses().add(address);
    });
    return new PersonDto(personRepository.save(person));
}

在此处输入图像描述

java

0 个回答

  1. Best Answer

    @JoinTable只需要在关联的一端指定。在将管理它的那个。在您的情况下，在 Person 中执行此操作是有意义的。

    现在，由于@JoinTable那里和那里，关联表中的条目在保存时Person和保存时都被保存Address。像这样正确：

    public class Person {
    ...
    @ManyToMany(cascade = CascadeType.ALL)
    @JoinTable(name = "persons_addresses",
            joinColumns = @JoinColumn(name = "person_id"),
            inverseJoinColumns = @JoinColumn(name = "address_id"))
    private List<Address> addresses;
}
public class Address {
    ...
    @ManyToMany(mappedBy="addresses")
    private List<Person> persons;
}

    mappedBy表示另一端（即 Person）是所有者并管理关联（即在保存时创建记录等）。

    为了简化关联的工作并保持内存中对象的一致性，通常会创建一个方法：

    class Person {
     public void addAddress(Address address) {
        this.addresses.add(address);
        address.getPersons().add(this);
     }
}
    • 1

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