使用JPA與Hibernate提供程序的ManyToMany關係不會創建主鍵

Question

我已經創建了兩個使用Hibernate作爲具有ManyToMany關係的提供程序的JPA實體（Client，InstrumentTraded）。讓Hibernate爲MySQL生成表之後，似乎ManyToMany關係表不包含這兩個外鍵的主鍵。這允許多對多表中的重複記錄，這不是所需的結果。

表生成：

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

優選表：

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

實體：

@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; 
    } 

    ... 

} 

做一些後研究它看起來像唯一的解決方案是mapping a join table with additional columns使用@OneToMany@IdClass和複合主鍵類，當我不需要額外的列。除了上面代碼中包含的解決方案之外，這是唯一的解決方案，它使用@UniqueConstraint以及@ManyToMany映射中的兩個外鍵列？對於像這樣的常見場景所需的工作量似乎有點荒謬。謝謝！

Answer 1

您的映射看起來很奇怪（特別是@JoinTable批註的joinColumn部分）。我希望這樣的事情：

@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，除非你想覆蓋缺省值（和我猜你這樣做），我只想跳過@JoinTable。

Answer 2

或者分裂您@ManyToMany到@OneToMany - @ManyToOne關係見here如何完成這個映射

Answer 3

下面就來解決這個問題的方法：

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; 

這是用於單向映射。如果您想要雙向關係，請將InstrumentTraded.class中的映射更改爲相同。

Answer 4

我有類似的問題。我所做的只是我從名單改變了集合類型設置：

private List<InstrumentTraded> instrumentsTraded; 

到

private Set<InstrumentTraded> instrumentsTraded; 

不知怎麼現在的Hibernate生成的連接表的主鍵。