休眠继承问题

Question

我在使用DiscriminatorColumn时从数据库加载表时遇到了问题。就实体扩展我的超类（ObjectA）而言，数据加载没有问题。新值出现在没有表扩展名的鉴别器列中时发生问题。我试图加载ObjctA的鉴别值不同于它在注解中指定的（ObjectTypes.GENERIC_OBJECT）。因为我正在使用IngeritanceType.JOINED我知道应该有一个带有id的子表来连接这些表，但是没有这样的表。我也不能添加它（需求）。

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我想要做的是加载ObjectA类的鉴别值不同于注释中指定的。我知道价值只接受一个价值。我还尝试创建扩展ObjectA的空类，并将dicriminator值设置为期望值。没有成功。 Hibernate把它当作实体并且找不到它。

有没有针对该场景的解决方法？

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我的实体是这样的：

@MappedSuperclass 
public abstract class AbstractEntity implements Serializable 
{... 

@Entity 
@Table(name = "objecta") 
@Inheritance(strategy = InheritanceType.JOINED) 
@DiscriminatorColumn(name = "objectclass", discriminatorType = DiscriminatorType.INTEGER) 
@DiscriminatorValue(ObjectTypes.GENERIC_OBJECT) 
@NamedQueries({...}) 
public class ObjectA extends AbstractEntity { 
... 

@Entity 
@Table(name = "objectb") 
@DiscriminatorValue(ObjectTypes.OBJECT_B) 
@NamedQueries({...}) 
public class ObjectB extends ObjectA{ 

public class ObjectTypes{ 
    public static final String GENERIC_OBJECT = "0"; 
    public static final String OBJECT_B= "1"; 
    public static final String OBJECT_C = "2";//no extension table for that object type, 
//it is the same as GENERI_OBJECT (no additional properties) 
    public static final String OBJECT_C = "3"; 
...} 

---

（编辑）问题：

我不能执行原生查询加载对象A的对象（但我可以加载它，当对象A作为子对象扩展装载）：

@NamedQueries({ @NamedQuery(name = ObjectA.FIND_BY_ID, query = "SELECT t FROM ObjectA t WHERE t.id = :id"), 
     @NamedQuery(name = ObjectA.FIND_ALL, query = "SELECT t FROM ObjectA t"), 
     @NamedQuery(name = ObjectA.TOTAL_RESULT, query = "SELECT count(t) from ObjectA t"), 
     @NamedQuery(name = ObjectA.FIND_BY_OBJECT_TYPE, query = "SELECT t FROM ObjectA t WHERE t.objecttype = :objectType") }) 
public class ObjectA extends AbstractEntity { 

    private static final long serialVersionUID = 8831394270398606926L; 
    public static final String FIND_BY_ID = "ObjectA.find"; 
    public static final String FIND_ALL = "ObjectA.findAll"; 
... 

//loading part 
    public List<ObjectA> findByObjectType(ObjectTypes objectType) { 
     return em.createNamedQuery(ObjectA.FIND_BY_OBJECT_TYPE, ObjectA.class).setParameter("objectType", objectType).getResultList(); 
    } 

堆栈跟踪：

Caused by: javax.persistence.PersistenceException: org.hibernate.type.SerializationException: could not deserialize 
    at org.hibernate.jpa.spi.AbstractEntityManagerImpl.convert(AbstractEntityManagerImpl.java:1692) 
    at org.hibernate.jpa.spi.AbstractEntityManagerImpl.convert(AbstractEntityManagerImpl.java:1602) 
    at org.hibernate.jpa.internal.QueryImpl.getResultList(QueryImpl.java:492) 
    at com.mypackage.repository.ObjectARepository.findAll(ObjectARepository.java:38) 
    at com.mypackage.database.DatabaseManager.init(DatabaseManager.java:77) 
    ... 240 more 
Caused by: org.hibernate.type.SerializationException: could not deserialize 
    at org.hibernate.internal.util.SerializationHelper.doDeserialize(SerializationHelper.java:243) 
    at org.hibernate.internal.util.SerializationHelper.deserialize(SerializationHelper.java:287) 
    at org.hibernate.type.descriptor.java.SerializableTypeDescriptor.fromBytes(SerializableTypeDescriptor.java:138) 
    at org.hibernate.type.descriptor.java.SerializableTypeDescriptor.wrap(SerializableTypeDescriptor.java:113) 
    at org.hibernate.type.descriptor.java.SerializableTypeDescriptor.wrap(SerializableTypeDescriptor.java:27) 
    at org.hibernate.type.descriptor.sql.VarbinaryTypeDescriptor$2.doExtract(VarbinaryTypeDescriptor.java:60) 
    at org.hibernate.type.descriptor.sql.BasicExtractor.extract(BasicExtractor.java:47) 
    at org.hibernate.type.descriptor.converter.AttributeConverterSqlTypeDescriptorAdapter$2.extract(AttributeConverterSqlTypeDescriptorAdapter.java:121) 
    at org.hibernate.type.AbstractStandardBasicType.nullSafeGet(AbstractStandardBasicType.java:238) 
    at org.hibernate.type.AbstractStandardBasicType.nullSafeGet(AbstractStandardBasicType.java:234) 
    at org.hibernate.type.AbstractStandardBasicType.nullSafeGet(AbstractStandardBasicType.java:224) 
    at org.hibernate.type.AbstractStandardBasicType.hydrate(AbstractStandardBasicType.java:300) 
    at org.hibernate.persister.entity.AbstractEntityPersister.hydrate(AbstractEntityPersister.java:2738) 
    at org.hibernate.loader.Loader.loadFromResultSet(Loader.java:1729) 
    at org.hibernate.loader.Loader.instanceNotYetLoaded(Loader.java:1655) 
    at org.hibernate.loader.Loader.getRow(Loader.java:1544) 
    at org.hibernate.loader.Loader.getRowFromResultSet(Loader.java:727) 
    at org.hibernate.loader.Loader.processResultSet(Loader.java:972) 
    at org.hibernate.loader.Loader.doQuery(Loader.java:930) 
    at org.hibernate.loader.Loader.doQueryAndInitializeNonLazyCollections(Loader.java:336) 
    at org.hibernate.loader.Loader.doList(Loader.java:2617) 
    at org.hibernate.loader.Loader.doList(Loader.java:2600) 
    at org.hibernate.loader.Loader.listIgnoreQueryCache(Loader.java:2429) 
    at org.hibernate.loader.Loader.list(Loader.java:2424) 
    at org.hibernate.loader.hql.QueryLoader.list(QueryLoader.java:501) 
    at org.hibernate.hql.internal.ast.QueryTranslatorImpl.list(QueryTranslatorImpl.java:371) 
    at org.hibernate.engine.query.spi.HQLQueryPlan.performList(HQLQueryPlan.java:216) 
    at org.hibernate.internal.SessionImpl.list(SessionImpl.java:1326) 
    at org.hibernate.internal.QueryImpl.list(QueryImpl.java:87) 
    at org.hibernate.jpa.internal.QueryImpl.list(QueryImpl.java:606) 
    at org.hibernate.jpa.internal.QueryImpl.getResultList(QueryImpl.java:483) 
    ... 242 more 
Caused by: java.io.StreamCorruptedException: invalid stream header: 7B227363 
    at java.io.ObjectInputStream.readStreamHeader(ObjectInputStream.java:806) 
    at java.io.ObjectInputStream.<init>(ObjectInputStream.java:299) 
    at org.hibernate.internal.util.SerializationHelper$CustomObjectInputStream.<init>(SerializationHelper.java:309) 
    at org.hibernate.internal.util.SerializationHelper$CustomObjectInputStream.<init>(SerializationHelper.java:299) 
    at org.hibernate.internal.util.SerializationHelper.doDeserialize(SerializationHelper.java:218) 
    ... 272 more 

Answer 1

当使用InheritanceType.JOINED没有必要对DiscriminatorColumn（这是为SINGLE_TABLE继承）。

为InheritanceType.JOINED，你需要在你的子类中的以下内容：

@PrimaryKeyJoinColumn(name = "parent_id", referencedColumnName = "id") 

为你的子类的表然后将需要的列parent_id，这既是primary key的表，该列的foreign keyid（主键）对应于超类的表中。