JPA - @MapKey和@EmbeddedId

Question

我有以下DB结构：

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​

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其中FESTIVAL_ID和LANG是复合PK，FESTIVAL_ID是节日的FK。

在我的Java代码中，我有以下实体：

@Embeddable
public class FestivalTranslationId {

    @Column(name = "FESTIVAL_ID")
    Long festivalId;

    @Column(name = "LANG")
    String lang;

    ...
}

public class FestivalTranslation {

    @EmbeddedId
    FestivalTranslationId id = new FestivalTranslationId();

    @MapsId(value = "festivalId")
    @ManyToOne
    @JoinColumn(name = "FESTIVAL_ID", referencedColumnName = "ID")
    Festival festival;

    @Column(name = "LANG")
    String lang;

    ...
}


@Entity
@Table(name = "FESTIVAL")
public class Festival {

    @OneToMany(mappedBy = "festival")
    @MapKey(name="lang")
    Map<String, FestivalTranslation> translations;

    ...
}

但是当我尝试获得节日实体时，我有一个例外：

com.mysql.jdbc.exceptions.jdbc4.MySQLSyntaxErrorException: Unknown column 'translatio0_.ID' in 'field list'

在hibernate日志中，我看到了疯狂的sql查询：

SELECT translatio0_.FESTIVAL_ID AS FESTIVAL1_14_0_,
       translatio0_.FESTIVAL_ID AS FESTIVAL1_15_0_,
       translatio0_.LANG AS LANG2_15_0_,
       translatio0_.ID AS ID3_15_0_,
       translatio0_.FESTIVAL_ID AS FESTIVAL1_15_1_,
       translatio0_.LANG AS LANG2_15_1_,
       translatio0_.ID AS ID3_15_1_
  FROM FESTIVAL_TRANSLATION translatio0_
 WHERE translatio0_.FESTIVAL_ID = ?

我的问题是，对于@EmbeddedId的实体是否可以使用Map，其中key是复合PK的一部分？

Answer 1

示例方法可以如下所示：

@Embeddable
public class FestivalId implements Serializable {
    @Column(name = "FESTIVAL_ID")
    private int id;
    ...
}

@Embeddable
public class FestivalTranslationId implements Serializable {
    @Embedded
    private FestivalId festivalId;

    @Column(name = "LANG")
    private String lang;
    ...
}

@Entity
@Table(name = "FESTIVAL")
public class Festival {
    @EmbeddedId
    @AttributeOverride(name = "id", column = @Column(name = "ID"))
    private FestivalId festivalId;

    @MapsId(value = "festivalId")
    @OneToMany(mappedBy = "festival")
    @MapKey(name = "festivalTranslationId")
    private Map<String, FestivalTranslation> translations;
    ...
}

@Entity
@Table(name = "FESTIVAL_TRANSLATION")
public class FestivalTranslation {
    @EmbeddedId
    private FestivalTranslationId festivalTranslationId;

    @ManyToOne
    private Festival festival;
    ...
}

上述实体编制了以下表格：

FESTIVAL            FESTIVAL_TRANSLATION
--------            --------------------
ID    PK            FESTIVAL_ID    FK PK
                    LANG              PK

用Hibernate 4.3.8进行测试。

Answer 2

如果您想从lang实体访问Festival属性，就不能直接这样做，因为Festival中没有lang映射。您必须这样做：@MapKey(name="id.lang")，因为它是通过FestivalTranslationId访问的。

有一个非常类似的问题描述了这里。但是，看起来可能存在一些问题，因为lang映射既存在于映射的键中，也存在于映射的值中(这取决于实际使用的JPA提供程序--Hibernate中存在问题)。