将唯一约束关联为JPA中的外键

Question

这是我的场景，我试图通过使用@JoinColumn与列a1, a2, a3的OneToMany关系将实体B关联到实体A，我得到了错误referenced column names not mapped to a single property。后来我尝试了@Uniqueconstraint与a1, a2和a3列在表A上，我不能成功。有谁能帮我把实体B和A关联为@ onmany关系吗?

A
--
a1
a2
a3
PrimaryKey -- a1 and a2
B
--
a1
a2
a3
b1
b2
PrimaryKey -- a1, a2, a3, and b1
@Entity
@Table(name = "A")
Class A
{
    @EmbeddedId
    private APK apk;
    @Column(name="a3")
    private Integer a3;
    @OneToMany(mappedBy="a")
    private Set<B> bSet;
}
@Embeddable
Class APK
{
    @Column(name="a1")
    private Integer a1;
    @Column(name="a2")
    private Integer a2;     
}
@Entity
@Table(name = "B")
Class B
{
    @EmbeddedId
    private BPK bpk;
    @Column(name="b2")
    private Integer b2;
    @ManyToOne
    @JoinColumns({
        @JoinColumn(name="a1", referencedColumnName="a1", insertable=false, updatable=false),
        @JoinColumn(name="a2", referencedColumnName="a2", insertable=false, updatable=false),
        @JoinColumn(name="a3", referencedColumnName="a3", insertable=false, updatable=false)
    })
    private A a;
}
@Embeddable
Class BPK
{
    @Column(name="a1")
    private Integer a1;
    @Column(name="a2")
    private Integer a2; 
    @Column(name="a3")
    private Integer a2;     
    @Column(name="b1")
    private Integer b1; 
}

Answer 1

a3不是A的主键的一部分，因此在B表中不应该需要。

有几种方法可以映射这个，但如果使用JPA 2.1，我会使用:

@Entity
@Table(name = "A")
Class A
{
    @EmbeddedId
    private APK apk;
    @Column(name="a3")
    private Integer a3;
    @OneToMany(mappedby='a')
    List bList;
}
@Embeddable
Class APK
{
    @Column(name="a1")
    private Integer a1;
    @Column(name="a2")
    private Integer a2;     
}

@Entity
@IdClass(BPK.class)
@Table(name = "B")
Class B
{
    @Id
    @Column(name="b1")
    private Integer b1; 
    @Column(name="b2")
    private Integer b2;
    @Id
    @ManyToOne
    @JoinColumns({
        @JoinColumn(name="a1", referencedColumnName="a1"),
        @JoinColumn(name="a2", referencedColumnName="a2")
    })
    private A a;
}
@Embeddable
Class BPK
{
    private APK a;     
    private Integer b1; 
}

有很多方法来映射它。