Hibernate继承问题(Hibernate inheritance issue)
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释中指定的（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）。
我正在尝试做的是加载ObjectA类，其识别符值与注释中指定的不同。 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。
有没有解决方案？
我的实体如下所示：
@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：
我无法通过执行本机查询加载ObjectA对象（但是我可以在ObjectA作为子对象扩展加载时加载它）：
@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 moreI have problem loading tables from database while using DiscriminatorColumn. As far as there is entity extending my super class (ObjectA), there is no problem with data loading. Problem occurred when new values appeared in discriminator column which do not have it table extension. I am trying to load ObjctA with discriminator value different than it is specified in annotation (ObjectTypes.GENERIC_OBJECT). Since I am using IngeritanceType.JOINED I know there should be a child table with the id to join these tables, but there is no such table. I can not add it also (requirements).
What I am trying to do, is to load ObjectA classes with discriminator value different than specified in annotation. I know that Value accepts only one value. I also tried to create empty class that extends ObjectA, and set dicriminator value to desired one. No success. Hibernate treat that as entity and can not find it.
Is there any workaround for that scenario?
My entities looks like this:
@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"; ...}
(edit)Issue:
I can not load ObjectA objects by executing native queries (but I can load it when ObjectA is loaded as child object extension):
@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(); }Stack trace:
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
原文：https://stackoverflow.com/questions/41826938
更新时间：2022-04-10 15:04
最满意答案
boost::iterator_range<directory_iterator> rng(directory_iterator(p), directory_iterator());这声明了一个函数不是一个对象。
您可以将其更改为：
boost::iterator_range<directory_iterator> rng = boost::iterator_range<directory_iterator>(directory_iterator(p), directory_iterator());或者在C ++ 11中：
auto rng = boost::iterator_range<directory_iterator>(directory_iterator(p), directory_iterator());但使用工厂功能更好：
boost::iterator_range<directory_iterator> rng = boost::make_iterator_range(directory_iterator(p), directory_iterator());通过使用
make_iterator_range你不需要命名迭代器的类型，它将从参数类型中推导出来。另一个问题是你正在写一个空的列表，这是未定义的行为，你应该使用插入迭代器来调用
push_back()就像在你的工作代码中一样。 把它放在一起：std::list<directory_entry> datFiles; boost::copy( boost::make_iterator_range(directory_iterator(p), directory_iterator()), std::back_inserter(datFiles) );在C ++ 11中它更简洁：
std::list<directory_entry> datFiles; boost::copy( boost::make_iterator_range(directory_iterator(p), {}), std::back_inserter(datFiles) );现在你可以很容易地添加过滤器：
std::list<directory_entry> datFiles; boost::copy( boost::make_iterator_range(directory_iterator(p), {}) | some_dir_filter, std::back_inserter(datFiles) );This line is hitting is the Most Vexing Parse:
boost::iterator_range<directory_iterator> rng(directory_iterator(p), directory_iterator());That declares a function not an object.
You can change it to:
boost::iterator_range<directory_iterator> rng = boost::iterator_range<directory_iterator>(directory_iterator(p), directory_iterator());Or in C++11:
auto rng = boost::iterator_range<directory_iterator>(directory_iterator(p), directory_iterator());But it's even better to use the factory function for it:
boost::iterator_range<directory_iterator> rng = boost::make_iterator_range(directory_iterator(p), directory_iterator());By using
make_iterator_rangeyou don't need to name the type of iterator, it will be deduced from the argument types.The other problem is that you're writing to an empty list, which is undefined behaviour, you should use an insert iterator to call
push_back()like in your working code. Putting it all together:std::list<directory_entry> datFiles; boost::copy( boost::make_iterator_range(directory_iterator(p), directory_iterator()), std::back_inserter(datFiles) );In C++11 it's more concise:
std::list<directory_entry> datFiles; boost::copy( boost::make_iterator_range(directory_iterator(p), {}), std::back_inserter(datFiles) );Now you could add the filter pretty easily:
std::list<directory_entry> datFiles; boost::copy( boost::make_iterator_range(directory_iterator(p), {}) | some_dir_filter, std::back_inserter(datFiles) );
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