java Hibernate原生查询与5.2.10

Question

在冬眠状态下<；在5.2中，可以使用通用SQL查询，如

String sql = "select a, b, sum (c) csum from a group by a, b";
SQLQuery q = session.createSqlQuery (sql);
q
    .addScalar ("a", IntegerType.INSTANCE)
    .addScalar ("b", IntegerType.INSTANCE)
    .addScalar ("csum", IntegerType.INSTANCE);
q.setResultTransformer (new AliasToBeanResultTransformer (RankingModel.class));
List<RankingModel> results = q.list ();

其中RankingModel看起来像：

public class RankingModel
{
    public int a, b, csum;
}

然而，在5.2中，addScalar()，setResultTransformer()都被弃用，建议使用session.createNativeQuery()。与上述内容最接近的等价物是：

String sql = "select a, b, sum (c) csum from a group by a, b";
NativeQuery<RankingModel> q = session.createNativeQuery (sql, RankingModel.class);
List<RankingModel> results = q.list ();

但是，此代码在以下情况下失败：

org.hibernate.MappingException: Unknown entity: ... RankingModel] with root cause
org.hibernate.MappingException: Unknown entity: ... RankingModel
    at org.hibernate.metamodel.internal.MetamodelImpl.entityPersister(MetamodelImpl.java:620)
    at org.hibernate.engine.spi.SessionFactoryImplementor.getEntityPersister(SessionFactoryImplementor.java:335)
    at org.hibernate.loader.custom.sql.SQLQueryReturnProcessor.getSQLLoadable(SQLQueryReturnProcessor.java:358)
    at org.hibernate.loader.custom.sql.SQLQueryReturnProcessor.processRootReturn(SQLQueryReturnProcessor.java:411)
    at org.hibernate.loader.custom.sql.SQLQueryReturnProcessor.processReturn(SQLQueryReturnProcessor.java:378)
    at org.hibernate.loader.custom.sql.SQLQueryReturnProcessor.process(SQLQueryReturnProcessor.java:180)
    at org.hibernate.loader.custom.sql.SQLCustomQuery.<init>(SQLCustomQuery.java:71)
    at org.hibernate.engine.query.internal.NativeQueryInterpreterStandardImpl.createQueryPlan(NativeQueryInterpreterStandardImpl.java:70)
    at org.hibernate.engine.query.spi.QueryPlanCache.getNativeSQLQueryPlan(QueryPlanCache.java:213)
    at org.hibernate.internal.AbstractSharedSessionContract.getNativeQueryPlan(AbstractSharedSessionContract.java:550)
    at org.hibernate.internal.AbstractSharedSessionContract.list(AbstractSharedSessionContract.java:992)
    at org.hibernate.query.internal.NativeQueryImpl.doList(NativeQueryImpl.java:148)

有人知道我错过了什么吗

Answer 1

为了告诉Hibernate使用像RankingModel.java这样的自定义实体（数据bean）类，必须根据JPA规范，用@Entity注释每个这样的类，用@Id或@Column注释每个可赋值列（字段）。事实上，Hibernate尽最大努力尊重JPA2.0契约，并支持javax.persistence包中的所有相关Java注释

执行此操作时，请确保每个实体类都有一个唯一的标识符字段，如hibernate exception: org.hibernate.AnnotationException: No identifier specified for entity: com..domain.idea.MAE_MFEView

以下是实体类的外观：

@Entity
public class RankingModel
{
    @Id
    public int id;

    @Column
    public int a;

    @Column
    public int b;

    @Column
    public int csum;
}

如果要将实体持久化到数据库中，那么类也必须用@Table注释。这会明确地告诉Hibernate实体持久化要使用哪个数据库表。我认为，对于仅获取数据而言，注释是不必要的

最后，告诉Hibernate实际查找所有（带注释的）实体类。这可以通过从hbm.xml引用它们来实现，或者，对于像我这样的Java纯粹主义者，可以通过将要扫描的Java包列为LocalSessionFactoryBean构造函数的参数来实现，正如How to scan packages for Hibernate entities instead of using hbm.xml?中很好地解释的那样

Answer 2

String sql = "SELECT a, b, sum(c) csum FROM a GROUP BY a, b";
NativeQuery<RankingModel> q = session.createNativeQuery(sql, RankingModel.class);
List<RankingModel> results = q.list();

Answer 3

你可以尝试使用

String sql = "select a, b, sum (c) csum from a group by a, b";
NativeQuery<?> q = session.createNativeQuery (sql);
List<RankingModel> results = (List<RankingModel>)q.list ();

它可以工作，但在IDE中会发出警告

或者

String sql = "select a, b, sum (c) csum from a group by a, b";
    NativeQuery<?> q = session.createNativeQuery (sql).addSynchronizedEntityClass( RankingModel.class );
    List<RankingModel> results = (List<RankingModel>)q.list ();