无法使用 @IdClass 转换实体中的请求元素答案

【问题标题】：Failed to convert request element in entity with @IdClass无法使用 @IdClass 转换实体中的请求元素
【发布时间】：2017-01-04 06:54:51
【问题描述】：

我有以下设置：

@Entity
@IdClass(MemberAttributePk.class)
public class MemberAttribute {
    @Id
    @ManyToOne @JoinColumn(name="member_id")
    protected Member member;

    @Id
    protected String name;

    private String value;

    public MemberAttribute() {}

    // get & set
}

还有id类：

public class MemberAttributePk implements Serializable {
    protected Member member;
    protected String name;

    public MemberAttributePk() {}

    // get & set
}

我已经为MemberAttribute 定义了一个简单的 Spring Data 存储库：

@Repository
public interface MemberAttributeRepo extends JpaRepository<MemberAttribute, MemberAttributePk> {
}

现在，我要做的就是将成员属性持久化到数据库中：

public void saveAttribute(Member member, String name, String value) {
    MemberAttribute attr = new MemberAttribute(member, name, value);
    attributeRepo.save(attr);
}

但是，我最终得到了这个服务器异常：

2016-08-28 00:24:20.673  WARN 5656 --- [nio-8080-exec-8] .w.s.m.s.DefaultHandlerExceptionResolver : 
Failed to convert request element: org.springframework.beans.ConversionNotSupportedException: 
Failed to convert property value of type [java.lang.Long] to required type [com.example.Member] for property 'member'; nested exception is java.lang.IllegalStateException: 
Cannot convert value of type [java.lang.Long] to required type [com.example.Member] for property 'member': 
no matching editors or conversion strategy found

知道我做错了什么吗？谢谢！

【问题讨论】：

标签： java spring hibernate spring-data

【解决方案1】：

只是您的代码不符合 JPA。问题的原因是您使用Member 作为您的PK 的一部分。 PK只能由以下Java类型的字段组成

原语 : boolean , byte , char , int , long , short

java.lang : Boolean , Byte , Character , Integer , Long , Short , String , Enum , StringBuffer

java.math：BigInteger java.sql：日期、时间、时间戳

java.util：日期、货币、语言环境、时区、UUID

java.net：URI、URL

javax.jdo.spi：PersistenceCapable

这应该可行：

@Embeddable
public class MemberAttributePk implements Serializable {
    @Column(name = "member_id")
    protected Long memberId;
    @Column(name = "name")
    protected String name;

    public MemberAttributePk() {}

    // get & set
}

@Entity
public class MemberAttribute {

    @EmbeddedId
    protected MemberAttributePk memberAttributePk;

    @ManyToOne 
    @JoinColumn(name="member_id")
    protected Member member;

    private String value;

    public MemberAttribute() {}

    // get & set
}

或者@ClassId也一样

public class MemberAttributePk implements Serializable {
    protected Long memberId;
    protected String name;

    public MemberAttributePk() {}

    // get & set
}

@Entity
@IdClass(MemberAttributePk.class)
public class MemberAttribute {
    @Id
    @Column(name = "member_id")
    protected Long memberId;

    @Id
    @Column(name = "name")
    protected String name;

    @ManyToOne 
    @JoinColumn(name="member_id")
    protected Member member;

    private String value;

    public MemberAttribute() {}

    // get & set
}

【讨论】：

谢谢！而已。顺便提一下Member 应该映射为：@ManyToOne @JoinColumn(name="member_id", insertable = false, updatable = false)

【解决方案2】：

您可以尝试使用您的 MemberRepository 保存它，因为我相信您的 Member 类和 MemberAttribute 类具有一对多的关系引用，下面是示例

会员等级

@Entity
public class Member {

    @Id
    @GeneratedValue(strategy = GenerationType.AUTO)
    public long id;

    @OneToMany(mappedBy = "Member", cascade = CascadeType.ALL)
     private Set<MemberAttribute> mMemberAttributes = new HashSet<>();

     public void setMemberAttributes(Set<MemberAttribute> mMemberAttributes){
        this.mMemberAttributes = mMemberAttributes;
     }

     public Set<MemberAttribute> getMemberAttributes(){
         return mMemberAttributes;
     }

     // other code
}

MemberRepository 类

public interface MemberRepository extends JpaRepository<Member, Long> {

}

保存函数中的代码

public void saveAttribute(Member member, String name, String value) {
    MemberAttribute attr = new MemberAttribute(member, name, value);
    member.getMemberAttributes().add(attr);
    memberRepository.save(member);
}

【讨论】：