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如何從Spring-Data-JPA返回單個結果？

[英]How to return a single result from Spring-Data-JPA?

 原文  2014-03-17 20:46:57  9   2    java/ jpa/ spring-data/ spring-data-jpa

問題描述

我試圖從Spring Data查詢中獲得單個結果。 我想從用戶表中返回最大的ID。 我希望它會很簡單，但我有點失落。

到目前為止，基於這個相關的SO帖子 ，我得出結論，我需要使用Specification來定義我的查詢和Page d結果，指定我想要檢索的結果數。 不幸的是，我得到了一個HibernateJdbcException數據訪問異常。

我的Specification / Predicate應該相當簡單並反映： from User order by id ： 

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);

異常拋出： 

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

我有點迷失Hibernate錯誤 - 它要求一個group子句。 我認為它與我創建謂詞的方式有關，但我不知道如何創建這樣的簡單謂詞。

編輯

正如@OliverGierke所建議的，我試圖刪除root = query.from(User.class)但是hibernate仍然會拋出相同的錯誤（我啟用了完整的hibernate查詢跟蹤）。 然而，奇怪的是，這次，生成的SQL中沒有GROUP BY ，所以我比以前更加困惑。 

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]

2 個解決方案

解決方案1
 12  2014-03-19 13:11:28

我不確定你為什么要獲取一個集合來獲得單個結果。 如果我錯了，請糾正我，但正如我所解釋的那樣，解決問題的方法很容易使用@Query來解決。 將以下內容添加到存儲庫界面。 

@Query("SELECT max(t.id) FROM #{#entityName} t")
Integer getMaxId();

解決方案2
 11 已采納  2014-03-18 07:31:01

你沒有使用root進入Specification實例來調用.get(…)方法。 這使實例無法注冊正在使用的id ，從而透明地將其添加到結果集中。

只需刪除root = query.from(User.class); 應該做的伎倆。

令我感到困惑的是，你提到你打算建立一個“通過id查找”查詢。 你實際建立的是“按ID排序”。 如果它真的是你想要的前者，那么你可以使用CrudRepository上預定義的findOne(…)方法。

鑒於以下評論，您實際上想要實現的是找到ID最小的單個用戶。 這也可以通過簡單地擴展PagingAndSortingRepository然后使用像這樣的客戶端代碼來實現： 

interface UserRepository extends PagingAndSortingRepository<User, Long> { … }

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

這會將結果限制為第一頁的頁面大小為1，並按ID遞增排序。

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