java - 如何使用 Hibernate 仅获取一列的值

Question

我刚刚开始使用 Hibernate 进行开发，在尝试选择表中的列时遇到问题。我有一个表，其中有一列名为“nome”，它是一个字符串。我想要做的就是获取表中该列的所有值。为此，我创建了方法:

public List<String> obtemNomePorQuery(String query) {

        EntityManager manager = getEntityManager();

        Session session = manager.unwrap(Session.class);    

        List<String> listResult = (List<String>) session.createQuery(query).list();
        manager.close();

        return listResult;
    }

在这种情况下，我在查询参数中传递“select nome from lojas”。在 MySQL 中，我可以运行这个查询，它会返回我想要的一切。使用 Hibernate 我得到以下日志:

org.springframework.web.util.NestedServletException: Request processing failed; nested exception is org.hibernate.hql.internal.ast.QuerySyntaxException: lojas is not mapped [select nome from lojas]
    org.springframework.web.servlet.FrameworkServlet.processRequest(FrameworkServlet.java:656)
    org.springframework.web.servlet.FrameworkServlet.doGet(FrameworkServlet.java:549)
    javax.servlet.http.HttpServlet.service(HttpServlet.java:621)
    javax.servlet.http.HttpServlet.service(HttpServlet.java:728)
root cause

org.hibernate.hql.internal.ast.QuerySyntaxException: lojas is not mapped [select nome from lojas]
    org.hibernate.hql.internal.ast.util.SessionFactoryHelper.requireClassPersister(SessionFactoryHelper.java:180)
    org.hibernate.hql.internal.ast.tree.FromElementFactory.addFromElement(FromElementFactory.java:110)
    org.hibernate.hql.internal.ast.tree.FromClause.addFromElement(FromClause.java:93)
    org.hibernate.hql.internal.ast.HqlSqlWalker.createFromElement(HqlSqlWalker.java:326)
    org.hibernate.hql.internal.antlr.HqlSqlBaseWalker.fromElement(HqlSqlBaseWalker.java:3252)
    org.hibernate.hql.internal.antlr.HqlSqlBaseWalker.fromElementList(HqlSqlBaseWalker.java:3141)
    org.hibernate.hql.internal.antlr.HqlSqlBaseWalker.fromClause(HqlSqlBaseWalker.java:694)
    org.hibernate.hql.internal.antlr.HqlSqlBaseWalker.query(HqlSqlBaseWalker.java:550)
    org.hibernate.hql.internal.antlr.HqlSqlBaseWalker.selectStatement(HqlSqlBaseWalker.java:287)
    org.hibernate.hql.internal.antlr.HqlSqlBaseWalker.statement(HqlSqlBaseWalker.java:235)
    org.hibernate.hql.internal.ast.QueryTranslatorImpl.analyze(QueryTranslatorImpl.java:248)
    org.hibernate.hql.internal.ast.QueryTranslatorImpl.doCompile(QueryTranslatorImpl.java:183)
    org.hibernate.hql.internal.ast.QueryTranslatorImpl.compile(QueryTranslatorImpl.java:136)
    org.hibernate.engine.query.spi.HQLQueryPlan.<init>(HQLQueryPlan.java:101)
    org.hibernate.engine.query.spi.HQLQueryPlan.<init>(HQLQueryPlan.java:80)
    org.hibernate.engine.query.spi.QueryPlanCache.getHQLQueryPlan(QueryPlanCache.java:119)
    org.hibernate.internal.AbstractSessionImpl.getHQLQueryPlan(AbstractSessionImpl.java:214)
    org.hibernate.internal.AbstractSessionImpl.createQuery(AbstractSessionImpl.java:192)
    org.hibernate.internal.SessionImpl.createQuery(SessionImpl.java:1537)
    com.puccamp.projetofinal.persistence.Dao.obtemNomePorQuery(Dao.java:198)
    com.puccamp.projetofinal.controller.LojaController.gerenciaLoja(LojaController.java:63)
    sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
    sun.reflect.NativeMethodAccessorImpl.invoke(Unknown Source)
    sun.reflect.DelegatingMethodAccessorImpl.invoke(Unknown Source)
    java.lang.reflect.Method.invoke(Unknown Source)
    org.springframework.web.bind.annotation.support.HandlerMethodInvoker.invokeHandlerMethod(HandlerMethodInvoker.java:176)
    org.springframework.web.servlet.mvc.annotation.AnnotationMethodHandlerAdapter.invokeHandlerMethod(AnnotationMethodHandlerAdapter.java:426)
    org.springframework.web.servlet.mvc.annotation.AnnotationMethodHandlerAdapter.handle(AnnotationMethodHandlerAdapter.java:414)
    org.springframework.web.servlet.DispatcherServlet.doDispatch(DispatcherServlet.java:790)
    org.springframework.web.servlet.DispatcherServlet.doService(DispatcherServlet.java:719)
    org.springframework.web.servlet.FrameworkServlet.processRequest(FrameworkServlet.java:644)
    org.springframework.web.servlet.FrameworkServlet.doGet(FrameworkServlet.java:549)
    javax.servlet.http.HttpServlet.service(HttpServlet.java:621)
    javax.servlet.http.HttpServlet.service(HttpServlet.java:728)

我可能做错了什么？

Answer 1

您使用的方法需要 HQL，而不是 SQL。是否存在与 lojas 表关联的持久对象？如果不是，HQL 不适合您，您将需要获得与数据库的 native 连接来执行 SQL。您是否尝试过 Session 的 createSQLQuery(String queryString) 方法？这是javadoc:http://docs.jboss.org/hibernate/orm/3.5/javadoc/org/hibernate/Session.html