Question

我有以下问题：

我有一个带有复合主键的基类（用作超类）。现在我正在尝试从基类中正确设置子类，但这不起作用！有人能帮帮我吗？感谢

以下是我的课程：

BasePK.java

@Embeddable
public class BasePK implements Serializeable {
  protected String base1;
  protected Timestamp base2;
  ..
}

Base.java

@MappedSuperclass
@Inheritance(strategy=InheritanceType.TABLE_PER_CLASS)
public abstract class Base implements Serializeable {
  @EmbeddedId
  protected BasePK id;
  ..
}

SubClassA.java

@Entity
public class SubClassA extends Base implements Serializeable {

  @OneToMany(cascade=CascadeType.ALL, fetch=FetchType.EAGER, mappedBy="attrA")
  protected List<SubClassB> attrsB;

  protected String attrA1;
  protected String attrA2;
  ..
}

SubClassB.java

@Entity
public class SubClassB extends Base implements Serializeable {

  @ManyToOne(fetch=FetchType.LAZY)
  private SubClassA attrA;

  protected String attrB1;
  protected String attrB2;
  ..
}

SubClassC.java

@Entity
public class SubClassC extends SubClassA implements Serializeable {


  protected String attrC1;
  protected String attrC2;
  ..
}

当我尝试运行项目时，会进行以下排除：

[EL Info]: 2012-11-01 23:31:18.739--ServerSession(2063330336)--EclipseLink, version: Eclipse Persistence Services - 2.4.1.v20121003-ad44345
[EL Warning]: metadata: 2012-11-01 23:31:19.199--ServerSession(2063330336)--Reverting the lazy setting on the OneToOne or ManyToOne attribute [controlledObject] for the entity class [class logyourlife.entities.ChangeRecord] since weaving was not enabled or did not occur.
[EL Severe]: 2012-11-01 23:31:19.229--ServerSession(2063330336)--Exception [EclipseLink-0] (Eclipse Persistence Services - 2.4.1.v20121003-ad44345): org.eclipse.persistence.exceptions.IntegrityException
Descriptor Exceptions: 
---------------------------------------------------------

Exception [EclipseLink-48] (Eclipse Persistence Services - 2.4.1.v20121003-ad44345): org.eclipse.persistence.exceptions.DescriptorException
Exception Description: Multiple writable mappings exist for the field [SUBCLASSB.BASE1].  Only one may be defined as writable, all others must be specified read-only.
Mapping: org.eclipse.persistence.mappings.ManyToOneMapping[attrA]
Descriptor: RelationalDescriptor(test.entities.SubClassB --> [DatabaseTable(SUBCLASSB)])

Exception [EclipseLink-48] (Eclipse Persistence Services - 2.4.1.v20121003-ad44345): org.eclipse.persistence.exceptions.DescriptorException
Exception Description: Multiple writable mappings exist for the field [SUBCLASSB.BASE2].  Only one may be defined as writable, all others must be specified read-only.
Mapping: org.eclipse.persistence.mappings.ManyToOneMapping[attrA]
Descriptor: RelationalDescriptor(test.entities.SubClassB --> [DatabaseTable(SUBCLASSB)])

fyi：所有类都会覆盖equals和hashcode方法。

Answer 1

首先，删除Base上的@Inheritance注释。它没有任何用途。

然后，尝试明确定义ManyToOne关联的连接列。对于嵌入式ID字段和与SubClassA的多对一关联，EclipseLink似乎默认使用相同的列名。有关使用此注释的示例，请参阅http://docs.oracle.com/javaee/6/api/javax/persistence/JoinColumn.html。

附注：复合ID既低效又难以处理。您应该考虑为所有实体使用自动生成的单列ID。一切都会容易得多。

尝试在Superclass中使用EmbeddedId

1 个答案: