使用 JPA 和 Hibernate 提供程序的多对多关系不会创建主键

Question

我使用 Hibernate 作为提供者创建了两个具有多对多关系的 JPA 实体（客户端、InstrumentTraded）。在让 Hibernate 为 MySQL 生成表之后，ManyToMany 关系表似乎不包含两个外键的主键。这允许多对多表中的重复记录，这不是我们想要的结果。

生成的表格：

client(id,name)  
instrument_traded(id,name)  
client_instrument_traded(FK client_id, FK instrument_traded_id)

首选表：

client_instrument_traded(PK,FK client_id, PK,FK instrument_traded_id)

实体：

@Entity
public class Client extends AbstractEntity<Integer> {

    private static final long serialVersionUID = 1L;

    @Basic(optional = false)
    @Column(nullable = false, length = 125)
    private String name;

    @ManyToMany(fetch = FetchType.LAZY)
    @JoinTable(joinColumns = {
        @JoinColumn}, inverseJoinColumns = {
        @JoinColumn(name = "instrument_traded_id")}, uniqueConstraints =
    @UniqueConstraint(name = "UK_client_instruments_traded_client_id_instrument_traded_id",
    columnNames = {"client_id", "instrument_traded_id"}))
    @ForeignKey(name = "FK_client_instruments_traded_client_id",
    inverseName = "FK_client_instruments_traded_instrument_traded_id")
    private List<InstrumentTraded> instrumentsTraded;

    public Client() {
    }

    public List<InstrumentTraded> getInstrumentsTraded() {
        return instrumentsTraded;
    }

    public void setInstrumentsTraded(List<InstrumentTraded> instrumentsTraded) {
        this.instrumentsTraded = instrumentsTraded;
    }

    ...
}



@Entity
@Table(uniqueConstraints = {
    @UniqueConstraint(name = "UK_instrument_traded_name", columnNames = {"name"})})
public class InstrumentTraded extends AbstractEntity<Integer> {

    private static final long serialVersionUID = 1L;

    @Basic(optional = false)
    @Column(nullable = false, length = 50)
    private String name;

    @ManyToMany(mappedBy = "instrumentsTraded", fetch = FetchType.LAZY)
    private List<Client> clients;

    public InstrumentTraded() {
    }

    public List<Client> getClients() {
        return clients;
    }

    public void setClients(List<Client> clients) {
        this.clients = clients;
    }

    ...

}

在做了一些研究之后，看起来唯一的解决方案是mapping a join table with additional columns 在我不需要其他列时使用@OneToMany @IdClass 和复合主键类。这是除了我在上面的代码中包含的唯一解决方案之外的唯一解决方案，它使用@UniqueConstraint 和@ManyToMany 映射上的两个外键列？像这样的常见场景所需的工作量似乎有点荒谬。谢谢！

Answer 1

您的映射看起来很奇怪（尤其是 @JoinTable 注释的 joinColumn 部分）。我希望是这样的：

@ManyToMany(fetch = FetchType.LAZY)
@JoinTable(
    joinColumns= 
        @JoinColumn(name="CLIENT_ID", referencedColumnName="ID"), 
    inverseJoinColumns=
        @JoinColumn(name="instrument_traded_id", referencedColumnName="ID"),
    uniqueConstraints=
        @UniqueConstraint(
            name="UK_client_instruments_traded_client_id_instrument_traded_id",
            columnNames = {"client_id", "instrument_traded_id"}
        )
)
@ForeignKey(name = "FK_client_instruments_traded_client_id",
inverseName = "FK_client_instruments_traded_instrument_traded_id")
private List<InstrumentTraded> instrumentsTraded;

但除非你想覆盖默认值（我猜你会这样做），否则我会跳过 @JoinTable。

Answer 2

或将您的@ManyToMany 拆分为@OneToMany - @ManyToOne 关系请参阅here 如何完成此映射

Answer 3

这里有一个解决问题的方法：

Client.java：

 @ManyToMany(fetch = FetchType.EAGER,cascade = CascadeType.ALL)
 @JoinTable(
        joinColumns = {@JoinColumn(name = "client_id")},
        inverseJoinColumns = {@JoinColumn(name = "instrument_traded_id")},
        uniqueConstraints = {@UniqueConstraint(
            columnNames = {"client_id", "instrument_traded_id"})}
)
 private List<InstrumentTraded> instrumentsTraded;

这用于单向映射。如果您想要双向关系，请将InstrumentTraded.class 中的映射更改为相同。

Answer 4

我遇到了类似的问题。我所做的只是将集合类型从 List 更改为 Set：

private List<InstrumentTraded> instrumentsTraded;

到

private Set<InstrumentTraded> instrumentsTraded;

Hibernate 现在以某种方式为连接表生成主键。