使用@IdClass的实体休眠@ManyToOne

如何解决使用@IdClass的实体休眠@ManyToOne

我刚刚在项目中添加了一个新实体，但现在它没有启动。我认为这与使@ManyToOne成为复合键的一部分有关，但是我不确定。我将问题归结为以下实体：

A.class：

@Table(name = "A")
@Entity
@IdClass(KeyA.class)
public class A {
    
   @Id
   private String aId;
    
   @Id
   @ManyToOne
   private B b;
    
   public String getaId() {
      return aId;
   }
    
   public void setaId(String aId) {
      this.aId = aId;
   }
    
   public B getB() {
      return b;
   }
    
   public void setB(B b) {
      this.b = b;
   }
}

B.class：

@Table(name = "B")
@Entity
@IdClass(KeyB.class)
public class B {
    
   @Id
   String bId;
    
   @Id
   String bId2;
    
   public String getbId() {
      return bId;
   }
    
   public void setbId(String bId) {
      this.bId = bId;
   }
    
   public String getbId2() {
      return bId2;
   }
    
   public void setbId2(String bId2) {
      this.bId2 = bId2;
   }
}

KeyA.class：

public class KeyA implements Serializable {
    
   private String aId;
   private String b;
}

KeyB.class

public class KeyB implements Serializable{
    
   public String bId;
   public String bId2;
}

引发异常：

        Error creating bean with name 'entityManagerFactory' defined in class path resource
        [...]
        Caused by: org.hibernate.HibernateException: Unable to instantiate default tuplizer [org.hibernate.tuple.component.PojoComponentTuplizer]
    [...]
    Caused by: java.lang.reflect.InvocationTargetException: null
        at sun.reflect.NativeConstructorAccessorImpl.newInstance0(Native Method) ~[na:1.8.0_201]
        at sun.reflect.NativeConstructorAccessorImpl.newInstance(NativeConstructorAccessorImpl.java:62) ~[na:1.8.0_201]
        at sun.reflect.DelegatingConstructorAccessorImpl.newInstance(DelegatingConstructorAccessorImpl.java:45) ~[na:1.8.0_201]
        at java.lang.reflect.Constructor.newInstance(Constructor.java:423) ~[na:1.8.0_201]
        at org.hibernate.tuple.component.ComponentTuplizerFactory.constructTuplizer(ComponentTuplizerFactory.java:104) ~[hibernate-core-5.4.12.Final.jar:5.4.12.Final]
        ... 43 common frames omitted
    Caused by: org.hibernate.PropertyNotFoundException: Could not locate field name [bId] on class [java.lang.String]
        at org.hibernate.internal.util.ReflectHelper.findField(ReflectHelper.java:371) ~[hibernate-core-5.4.12.Final.jar:5.4.12.Final]
        at org.hibernate.property.access.internal.PropertyAccessFieldImpl.<init>(PropertyAccessFieldImpl.java:34) ~[hibernate-core-5.4.12.Final.jar:5.4.12.Final]
        at org.hibernate.property.access.internal.PropertyAccessstrategyFieldImpl.buildPropertyAccess(PropertyAccessstrategyFieldImpl.java:26) ~[hibernate-core-5.4.12.Final.jar:5.4.12.Final]
        at org.hibernate.mapping.Property.getGetter(Property.java:311) ~[hibernate-core-5.4.12.Final.jar:5.4.12.Final]
        at org.hibernate.tuple.component.PojoComponentTuplizer.buildGetter(PojoComponentTuplizer.java:141) ~[hibernate-core-5.4.12.Final.jar:5.4.12.Final]

我尝试了一切，包括导入最新的javassist。我正在Java 1.8上运行Spring Boot 2.2.5.RELEASE（也发生在11中）

解决方法

您的A组合键

public class KeyA implements Serializable {

    private String aId;
    private String b;
}

的结构就好像B仅具有一个字符串ID（在此称为b），而实际上它本身具有复合键

public class KeyB implements Serializable{

    public String bId;
    public String bId2;
}

因此您必须更改KeyA才能正确表示该关系：

public class KeyA implements Serializable {

    private String aId;
    private KeyB keyB;
}

您应在KeyA中使用与拥有实体中标记为@Id完全相同的字段名称/类型。

因此，您应该通过以下方式更正KeyA：

public class KeyA implements Serializable {

    private String aId;
    private B b;
}

请参见documentation中的进一步说明和示例。