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社区首页 >问答首页 >如何从返回单个结果？

问如何从返回单个结果？
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Stack Overflow用户
提问于 2014-03-17 20:46:57
回答 2查看 43.4K关注 0票数 16

我试图从Spring数据查询中获得一个结果。我希望从用户表中返回最大的ID。我本来希望这会很简单，但我有点迷路了。

到目前为止，基于this related SO post，我得出的结论是，我需要使用Specification来定义查询和Paged结果，并指定要检索的结果的数量。不幸的是，我得到了一个HibernateJdbcException数据访问异常。

我的Specification/Predicate应该相当简单，并反映：from User order by id

代码语言：javascript
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Page<User> result =userRepository.findAll(new Specification<User>() {
    @Override
    public Predicate toPredicate(Root<User> root, CriteriaQuery<?> query, CriteriaBuilder cb) {
        query.orderBy(cb.desc(root.get("id")));
        return query.getRestriction();
    }
}, new PageRequest(0, 10));

MatcherAssert.assertThat(result.isFirstPage(), is(true));
User u = result.getContent().get(0);

引发的异常：

代码语言：javascript
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org.springframework.orm.hibernate3.HibernateJdbcException: JDBC exception on Hibernate data access: SQLException for SQL [n/a]; SQL state [90016]; error code [90016]; could not extract ResultSet; nested exception is org.hibernate.exception.GenericJDBCException: could not extract ResultSet
    at org.springframework.orm.hibernate3.SessionFactoryUtils.convertHibernateAccessException(SessionFactoryUtils.java:651)
    at org.springframework.orm.jpa.vendor.HibernateJpaDialect.translateExceptionIfPossible(HibernateJpaDialect.java:106)
    at org.springframework.orm.jpa.AbstractEntityManagerFactoryBean.translateExceptionIfPossible(AbstractEntityManagerFactoryBean.java:403)
    at org.springframework.dao.support.ChainedPersistenceExceptionTranslator.translateExceptionIfPossible(ChainedPersistenceExceptionTranslator.java:58)
    at org.springframework.dao.support.DataAccessUtils.translateIfNecessary(DataAccessUtils.java:213)
    at org.springframework.dao.support.PersistenceExceptionTranslationInterceptor.invoke(PersistenceExceptionTranslationInterceptor.java:163)
    at org.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:172)
    at org.springframework.data.jpa.repository.support.LockModeRepositoryPostProcessor$LockModePopulatingMethodIntercceptor.invoke(LockModeRepositoryPostProcessor.java:92)
    ...
    ...
Caused by: org.hibernate.exception.GenericJDBCException: could not extract ResultSet
    at org.hibernate.exception.internal.StandardSQLExceptionConverter.convert(StandardSQLExceptionConverter.java:54)
    at org.hibernate.engine.jdbc.spi.SqlExceptionHelper.convert(SqlExceptionHelper.java:126)
    at org.hibernate.engine.jdbc.spi.SqlExceptionHelper.convert(SqlExceptionHelper.java:112)
    at org.hibernate.engine.jdbc.internal.ResultSetReturnImpl.extract(ResultSetReturnImpl.java:89)
    at org.hibernate.loader.Loader.getResultSet(Loader.java:2065)
    at org.hibernate.loader.Loader.executeQueryStatement(Loader.java:1862)
    at org.hibernate.loader.Loader.executeQueryStatement(Loader.java:1838)
    at org.hibernate.loader.Loader.doQuery(Loader.java:909)
    at org.hibernate.loader.Loader.doQueryAndInitializeNonLazyCollections(Loader.java:354)
    at org.hibernate.loader.Loader.doList(Loader.java:2553)
    at org.hibernate.loader.Loader.doList(Loader.java:2539)
    at org.hibernate.loader.Loader.listIgnoreQueryCache(Loader.java:2369)
    at org.hibernate.loader.Loader.list(Loader.java:2364)
    at org.hibernate.loader.hql.QueryLoader.list(QueryLoader.java:496)
    at org.hibernate.hql.internal.ast.QueryTranslatorImpl.list(QueryTranslatorImpl.java:387)
    at org.hibernate.engine.query.spi.HQLQueryPlan.performList(HQLQueryPlan.java:231)
    at org.hibernate.internal.SessionImpl.list(SessionImpl.java:1264)
    at org.hibernate.internal.QueryImpl.list(QueryImpl.java:103)
    at org.hibernate.jpa.internal.QueryImpl.list(QueryImpl.java:573)
    at org.hibernate.jpa.internal.QueryImpl.getResultList(QueryImpl.java:449)
    at org.hibernate.jpa.criteria.compile.CriteriaQueryTypeQueryAdapter.getResultList(CriteriaQueryTypeQueryAdapter.java:67)
    at org.springframework.data.jpa.repository.query.QueryUtils.executeCountQuery(QueryUtils.java:406)
    at org.springframework.data.jpa.repository.support.SimpleJpaRepository.readPage(SimpleJpaRepository.java:433)
    at org.springframework.data.jpa.repository.support.SimpleJpaRepository.findAll(SimpleJpaRepository.java:332)
    at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
    at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:57)
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
    at java.lang.reflect.Method.invoke(Method.java:606)
    at org.springframework.data.repository.core.support.RepositoryFactorySupport$QueryExecutorMethodInterceptor.executeMethodOn(RepositoryFactorySupport.java:358)
    at org.springframework.data.repository.core.support.RepositoryFactorySupport$QueryExecutorMethodInterceptor.invoke(RepositoryFactorySupport.java:343)
    at org.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:172)
    at org.springframework.transaction.interceptor.TransactionInterceptor$1.proceedWithInvocation(TransactionInterceptor.java:96)
    at org.springframework.transaction.interceptor.TransactionAspectSupport.invokeWithinTransaction(TransactionAspectSupport.java:260)
    at org.springframework.transaction.interceptor.TransactionInterceptor.invoke(TransactionInterceptor.java:94)
    at org.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:172)
    at org.springframework.dao.support.PersistenceExceptionTranslationInterceptor.invoke(PersistenceExceptionTranslationInterceptor.java:155)
    ... 46 more
Caused by: org.h2.jdbc.JdbcSQLException: Column "USER1_.ID" must be in the GROUP BY list; SQL statement:
/* select count(generatedAlias0) from User as generatedAlias0, User as generatedAlias1 where 1=1 order by generatedAlias1.id desc */ select count(user0_.id) as col_0_0_ from user user0_ cross join user user1_ where 1=1 order by user1_.id desc [90016-173]
    at org.h2.message.DbException.getJdbcSQLException(DbException.java:331)
    at org.h2.message.DbException.get(DbException.java:171)
    at org.h2.message.DbException.get(DbException.java:148)
    at org.h2.expression.ExpressionColumn.updateAggregate(ExpressionColumn.java:166)
    at org.h2.command.dml.Select.queryGroup(Select.java:344)
    at org.h2.command.dml.Select.queryWithoutCache(Select.java:620)
    at org.h2.command.dml.Query.query(Query.java:314)
    at org.h2.command.dml.Query.query(Query.java:284)
    at org.h2.command.dml.Query.query(Query.java:36)
    at org.h2.command.CommandContainer.query(CommandContainer.java:91)
    at org.h2.command.Command.executeQuery(Command.java:195)
    at org.h2.jdbc.JdbcPreparedStatement.executeQuery(JdbcPreparedStatement.java:106)
    at org.hibernate.engine.jdbc.internal.ResultSetReturnImpl.extract(ResultSetReturnImpl.java:80)
    ... 78 more

我被Hibernate错误弄糊涂了--它要求一个group子句。我猜想这与我创建谓词的方式有关，但我不知道如何创建这样一个简单的谓词。

编辑

正如@OliverGierke所建议的，我试图删除root = query.from(User.class)，但是hibernate仍然抛出相同的错误(我启用了完全hibernate查询跟踪)。然而，奇怪的是，这一次生成的SQL中没有GROUP BY，所以我比以前更加困惑。

代码语言：javascript
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2014-03-18 11:59:44,475 [main] DEBUG org.hibernate.SQL - 
    /* select
        count(generatedAlias0) 
    from
        User as generatedAlias0 
    order by
        generatedAlias0.id desc */ select
            count(user0_.id) as col_0_0_ 
        from
            user user0_ 
        order by
            user0_.id desc
Hibernate: 
    /* select
        count(generatedAlias0) 
    from
        User as generatedAlias0 
    order by
        generatedAlias0.id desc */ select
            count(user0_.id) as col_0_0_ 
        from
            user user0_ 
        order by
            user0_.id desc
2014-03-18 11:59:44,513 [main] WARN  hibernate.engine.jdbc.spi.SqlExceptionHelper - SQL Error: 90016, SQLState: 90016
2014-03-18 11:59:44,513 [main] ERROR hibernate.engine.jdbc.spi.SqlExceptionHelper - Column "USER0_.ID" must be in the GROUP BY list; SQL statement:
/* select count(generatedAlias0) from User as generatedAlias0 order by generatedAlias0.id desc */ select count(user0_.id) as col_0_0_ from user user0_ order by user0_.id desc [90016-173]
spring-data
spring-data-jpa
java
jpa
EN

回答 2

Stack Overflow用户

回答已采纳

发布于 2014-03-18 07:31:01

您没有使用传递到Specification实例的Specification来调用.get(…)方法。这会使实例无法注册正在使用的id，从而透明地将其添加到结果集中。

简单地删除root = query.from(User.class);就可以做到这一点。

令我困惑的是，您提到您打算构建一个"find“查询。你实际上正在构建的是一个“查找全部由id命令”。如果确实是您想要的前者，则可以在findOne(…)上使用预定义的CrudRepository方法。

考虑到下面的注释，您真正想要实现的似乎是找到一个拥有最小id的用户。这也可以通过简单地扩展PagingAndSortingRepository，然后使用如下客户端代码来实现：

代码语言：javascript
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interface UserRepository extends PagingAndSortingRepository<User, Long> { … }

Page<User> users = repository.findAll(new PageRequest(0, 1, Direction.ASC, "id"));
User user = users.getContent.get(0);

这将将结果限制为第一页的页面大小为1，并按id进行升序。

票数 12
EN

Stack Overflow用户

发布于 2014-03-19 13:11:28

我不知道为什么要获取一个集合来获得一个结果。如果我错了，请纠正我，但正如我所解释的，解决问题的方法很容易使用@Query解决。将以下内容添加到存储库接口中。

代码语言：javascript
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@Query("SELECT max(t.id) FROM #{#entityName} t")
Integer getMaxId();
票数 13
EN
页面原文内容由Stack Overflow提供。腾讯云小微IT领域专用引擎提供翻译支持
原文链接：

https://stackoverflow.com/questions/22465018

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