Question

这是我的场景，我试图通过OneToMany关系使用@JoinColumn将实体B与实体A关联，其中列a1，a2，a3和i得到错误referenced column names not mapped to a single property。后来我在表A上尝试了@Uniqueconstraint a1，a2和a3列，但我无法成功。你们中的任何人可以帮助我将实体B与A关联为@OnToMany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主键的一部分，所以不应该在B表中使用。

有几种方法可以映射它，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; 
}

虽然有许多方法可以映射它。

将Uniqueconstraint作为JPA中的外键关联

1 个答案: