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

Question

我已经创建了两个使用Hibernate作为具有ManyToMany关系的提供程序的JPA实体（Client，InstrumentTraded）。让Hibernate为MySQL生成表之后，似乎ManyToMany关系表不包含这两个外键的主键。这允许多对多表中的重复记录，这不是所需的结果。

表生成：

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

优选表：

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; 
    } 

    ... 

} 

做一些后研究它看起来像唯一的解决方案是mapping a join table with additional columns使用@OneToMany@IdClass和复合主键类，当我不需要额外的列。除了上面代码中包含的解决方案之外，这是唯一的解决方案，它使用@UniqueConstraint以及@ManyToMany映射中的两个外键列？对于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（特别是@JoinTable批注的joinColumn部分）。我希望这样的事情：

@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; 

但是，除非你想覆盖缺省值（和我猜你这样做），我只想跳过@JoinTable。

Answer 2

或者分裂您@ManyToMany到@OneToMany - @ManyToOne关系见here如何完成这个映射

Answer 3

下面就来解决这个问题的方法：

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; 

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

Answer 4

我有类似的问题。我所做的只是我从名单改变了集合类型设置：

private List<InstrumentTraded> instrumentsTraded; 

到

private Set<InstrumentTraded> instrumentsTraded; 

不知怎么现在的Hibernate生成的连接表的主键。