使用JPA和Hibernate提供程序的ManyToMany关系不会创建主键

Question

我使用Hibernate作为具有ManyToMany关系的提供程序创建了两个JPA实体(Client,InstrumentTraded).让Hibernate为MySQL生成表后,看起来ManyToMany关系表不包含两个外键的主键.这允许多对多表中的重复记录,这不是期望的结果.

生成的表:

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

首选表格:

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在不需要额外列时使用和复合主键类映射连接表@OneToMany @IdClass和其他列.这是除了我在上面的代码中包含的那个之外的唯一解决方案,它@UniqueConstraint在@ManyToMany映射中使用了两个外键列吗？像这样的常见场景所需的工作量似乎有点荒谬.谢谢!

Answer 1

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;

至

private Set<InstrumentTraded> instrumentsTraded;

不知何故,Hibernate现在为连接表生成主键.

Answer 2

这是解决问题的方法:

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;

这适用于单向映射.如果需要双向关系,请将映射更改InstrumentTraded.class为相同.

Answer 3

您的映射看起来很奇怪（特别是注释joinColumn的部分@JoinTable）。我期望这样的事情：

@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.