无法保存实体可嵌入 ID答案

【问题标题】：Can't save entity Embeddable Id无法保存实体可嵌入 ID
【发布时间】：2019-03-01 00:07:58
【问题描述】：

我有EcranChamp 实体

@Entity
@IdClass(EcranChampId.class)
public class EcranChamp {

@Id
@ManyToOne(fetch = FetchType.LAZY)
@JoinColumn(name = "ecran")
Ecran ecran;


@Id
@ManyToOne(fetch = FetchType.LAZY)
@JoinColumn(name = "champ")
Champ champ;

...

还有EcranChampId

@Embeddable
public class EcranChampId implements Serializable  {    
private Champ champ;  
private Ecran ecran;
...

每次我尝试保存 EcranChamp 元素时都会出现以下错误

2018-09-25 12:15:42.889 WARN 14216 --- [nio-8092-exec-8] .wsmsDefaultHandlerExceptionResolver：无法转换请求元素：org.springframework.beans.ConversionNotSupportedException：无法转换属性值'java.lang.Long' 类型的属性'ecran' 需要类型'com.kepler.porttailclient.domain.model.Ecran'；嵌套异常是 java.lang.IllegalStateException：无法将类型“java.lang.Long”的值转换为属性“ecran”所需的类型“com.kepler.porttailclient.domain.model.Ecran”：找不到匹配的编辑器或转换策略 2018-09-25 12:15:42.889 WARN 14216 --- [nio-8092-exec-8] .wsmsDefaultHandlerExceptionResolver：已解决由处理程序执行引起的异常：org.springframework.beans.ConversionNotSupportedException：无法转换类型的属性值'java.lang.Long' 为属性'ecran' 所需的类型'com.kepler.porttailclient.domain.model.Ecran'；嵌套异常是 java.lang.IllegalStateException：无法将类型“java.lang.Long”的值转换为属性“ecran”所需的类型“com.kepler.porttailclient.domain.model.Ecran”：找不到匹配的编辑器或转换策略

【问题讨论】：

您使用@IdClass 注释指定实体的id 类为EcranChampId。因此，您必须将@Id 字段设为EcramChampId。添加@Id 类型为Ecran 和Champ 的两个字段不起作用。
请为这个问题添加一个解决方案，我会尝试一下
见How to create and handle composite primary key in JPA

标签： java spring spring-boot spring-data-jpa

【解决方案1】：

试试这样的：

@Entity
@Table(name = "<entity name>")
public class EcranChamp {

    @EmbeddedId
    @AttributeOverrides({ @AttributeOverride(name = "id_ecran", column = @Column(name = 
        "<column name>", nullable = false)),
    @AttributeOverride(name = "id_champ", column = @Column(name = "<column name>", nullable = false)) })
    EcranChampId id

    @ManyToOne(fetch = FetchType.LAZY)
    @JoinColumn(name = "id_ecran")
    Ecran ecran;

    @ManyToOne(fetch = FetchType.LAZY)
    @JoinColumn(name = "id_champ")
    Champ champ; 
   //getters & setters 
 }   


@Embeddable
public class EcranChampId implements Serializable  {   
  @Column(name = "id_champ", nullable = false) 
  private Long id_champ; 
  @Column(name = "id_ecran", nullable = false)  
  private Long id_ecran; 
  //getters & setters 
}

【讨论】：

一个附加问题如何避免为ecran 和id_ecran 创建两个列。
我不知道你的确切型号。但是您不需要在 EcramChamp 表中创建两列，只需字段 id_ecram。我认为 id_ecram 是您表中 PK/FK 的名称。编辑：我已经编辑我的答案更正确。 (@JoinColumn(name = "id_ecran")
我可以用private Ecran id_ecran;替换可嵌入元素private Long id_ecran; 吗？！？

【解决方案2】：

你应该使用@EmbeddedId注解。

请将您的 EcranChampId 类更改为：

@Embeddable
public class EcranChampId implements Serializable  {  

    @ManyToOne
    private Champ champ;

    @ManyToOne
    private Ecran ecran;

    //getters and setters
}

并将您的 EcranChamp 类更改为：

@Entity
@Table(name = "champ_has_ecran_table_name")
@AssociationOverrides({
    @AssociationOverride(name = "pk.champ", joinColumns = @JoinColumn(name = "champ_id"))
    @AssociationOverride(name = "pk.ecran", joinColumns = @JoinColumn(name = "ecran_id"))
})
public class EcranChamp {

    @EmbeddedId
    private EcranChampId pk;

    public EcranChamp() {
        pk = new EcranChampId();
    }

    public EcranChampId getPk() {
        return pk;
    }

    public void setPk(EcranChampId pk) {
        this.pk = pk;
    }

    @Transient
    public Champ getChamp() {
        return pk.getChamp();
    }

    public void setChamp(Champ champ) {
        pk.setChamp(champ);
    }

    @Transient
    public Ecran getEcran() {
        return pk.getEcran();
    }

    public void setChamp(Ecran ecran) {
        pk.setEcran(ecran);
    }
}

并像这样使用它：

public class Champ {

    @OneToMany(mappedBy = "pk.champ")
    private Collection<EcranChamp> ecranChamps;

    //getters and setters
}

另外，如果EcranChamp 或EcranChampId 没有其他字段，我建议您使用@ManyToMany 注释而不是EcranChamp 类，如下所示：

public class Champ {

    @ManyToMany
    @JoinTable(
        name = "champ_has_ecran_table_name",
        joinColumns = @JoinColumn(name = "champ_id", referencedColumnName = "id", nullable = false),
        inverseJoinColumns = @JoinColumn(name = "ecran_id", referencedColumnName = "id", nullable = false)
    )
    private Collection<Ecran> ecrans;

    //getters and setters
}

【讨论】：