JPA关联表映射，其中实体之一具有组合键

Question

我有以下模型需要使用JPA进行注释：

• 商家（merchant_id，...）。

• MerchantType（id1，id2，...）

• MerchantMerchantTypeAssociationTable（merchant_id，id1，id2）

我不知道如何映射关联表。 Mapping Merchant非常困难，因此我将其保留在映射之外。 其他映射如下：

MerchantType ：

@Entity
class MerchantType {

    @EmbeddedId
    @AttributeOverrides({
         @AttributeOverride(name = "e1_id", column=@Column(name="e1_id")),
         @AttributeOverride(name = "another_id", column=@Column(name="another_id"))
    })        
    MerchantTypePk id;

    @ManyToOne
    @JoinColumn(name = "e1_id", referencedColumnName = "e1_id", insertable = false, nullable = false)
    @MapsId("e1_id")
    AnotherEntity1 e1;


    @Column(name = "another_id", referencedColumnName = "another_id", insertable = false, nullable = false)
    Long anotherId;

    //Two other local fields irrelevant to the discussion here

    public MerchantType(){
        this.id = new MerchantTypePk();
    }

    //Getters and setters here.
}

//MerchantTypePk is a simple Embeddable class here below with two Long fields:
//e1_id and another_id

MerchantMerchantTypeAssociation ：

@Entity
class MerchantMerchantTypeAssociation {

     @EmbeddedId
     @AttributeOverrides({
           @AttributeOverride(name = "e1_id", column = @Column(name = "e1_id")),
           @AttributeOverride(name = "another_id", column = @Column(name = "another_id"))
           @AttributeOverride(name = "offer_id", column = @Column(name = "merchant_id"))
     })
     private MerchantMerchantTypeAssociationPk id;
     //******** HERE IS THE QUESTION
     //******** HERE IS THE QUESTION
     //******** HERE IS THE QUESTION
     @ManyToOne
     @JoinColumns({
          @JoinColumn(name = "e1_id", referencedColumnName = "e1_id", insertable = false, updatable = false),
          @JoinColumn(name = "another_id", referencedColumnName = "another_id", insertable = false, updatable = false)
     })
     @MapsId("e1_id")
     @MapsId("another_id")
     private MerchantType merchantType;

     //Similar mapping to the one above, but with only one Join Column  
     private Merchant merchant;

     //One more local field that is irrelevant to the mapping
     //but is the one that is forcing me to map a many - to - many relationship
     //in this way.

}

//MerchantMerchantTypeAssociationPk as a simple embeddable

问题：当注释“ @MapsId”不能重复且不接受多个值时，如何为此类实体进行映射？

Answer 1

您没有包括MerchantMerchantTypeAssociationPk的代码，但是我猜测它看起来像这样：

@Embeddable
public class MerchantMerchantTypeAssociationPk {
    public MerchantPk merchantPK;
    public MerchantTypePk merchantTypePK;
}

@MapsId用来指明该关系属性对应，而不是列的复合关键字中的属性 。 因此， MerchantMerchantTypeAssociation应该如下所示：

@Entity class MerchantMerchantTypeAssociation {

    @EmbeddedId
    private MerchantMerchantTypeAssociationPk id;

    @ManyToOne
    @JoinColumns({
         @JoinColumn(name = "e1_id", referencedColumnName = "e1_id",...),
         @JoinColumn(name = "e2_id", referencedColumnName = "e2_id",...)
    })
    @MapsId("merchantTypePK") // <<< *attribute* in Embeddable
    private MerchantType merchantType;

    @ManyToOne
    @JoinColumn(name = "m_id", referencedColumnName = "merchant_id",...)
    @MapsId("merchantPK") // <<< *attribute* in Embeddable
    private Merchant merchant;
}

JPA 2.1规范的第2.4.1节中讨论了派生身份。