java - JPA 中的 getSingleResult() 抛出异常

Question

我正在使用 JPA 查询，当我使用

query.getSingleResult();

它正在抛出异常。我很清楚，如果有多个记录与参数匹配，该方法会抛出异常，但在我的例子中，参数是一个主键，所以这意味着结果是唯一的。但是当我使用

而不是上面的方法时

query.getResultList();

我没有这样的问题。我很困惑。同样，当我使用该方法时

query.setMaxResults(some value);

然后尝试获取结果列表，我的程序抛出了很多错误......!

javax.persistence.PersistenceException: org.hibernate.exception.SQLGrammarException: You have an error in your SQL syntax; check the manual that corresponds to your MySQL server version for the right syntax to use near '2 registered0_.id as id0_, registered0_.current_status as current2_0_, registere' at line 1
    at org.hibernate.ejb.AbstractEntityManagerImpl.convert(AbstractEntityManagerImpl.java:1360)
    at org.hibernate.ejb.AbstractEntityManagerImpl.convert(AbstractEntityManagerImpl.java:1288)
    at org.hibernate.ejb.QueryImpl.getSingleResult(QueryImpl.java:313)
    at com.aces.servlets.UserStatusServlet.getStatus(UserStatusServlet.java:193)
    at com.aces.servlets.UserStatusServlet.access$0(UserStatusServlet.java:188)
    at com.aces.servlets.UserStatusServlet$1.onComplete(UserStatusServlet.java:50)
    at org.apache.catalina.core.AsyncListenerWrapper.fireOnComplete(AsyncListenerWrapper.java:40)
    at org.apache.catalina.core.AsyncContextImpl.fireOnComplete(AsyncContextImpl.java:119)
    at org.apache.coyote.AsyncStateMachine.asyncPostProcess(AsyncStateMachine.java:190)
    at org.apache.coyote.AbstractProcessor.asyncPostProcess(AbstractProcessor.java:116)
    at org.apache.coyote.AbstractProtocol$AbstractConnectionHandler.process(AbstractProtocol.java:593)
    at org.apache.tomcat.util.net.JIoEndpoint$SocketProcessor.run(JIoEndpoint.java:312)
    at java.util.concurrent.ThreadPoolExecutor.runWorker(Unknown Source)
    at java.util.concurrent.ThreadPoolExecutor$Worker.run(Unknown Source)
    at java.lang.Thread.run(Unknown Source)
Caused by: org.hibernate.exception.SQLGrammarException: You have an error in your SQL syntax; check the manual that corresponds to your MySQL server version for the right syntax to use near '2 registered0_.id as id0_, registered0_.current_status as current2_0_, registere' at line 1
    at org.hibernate.exception.internal.SQLExceptionTypeDelegate.convert(SQLExceptionTypeDelegate.java:83)
    at org.hibernate.exception.internal.StandardSQLExceptionConverter.convert(StandardSQLExceptionConverter.java:49)
    at org.hibernate.engine.jdbc.spi.SqlExceptionHelper.convert(SqlExceptionHelper.java:125)
    at org.hibernate.engine.jdbc.spi.SqlExceptionHelper.convert(SqlExceptionHelper.java:110)
    at org.hibernate.engine.jdbc.internal.proxy.AbstractStatementProxyHandler.continueInvocation(AbstractStatementProxyHandler.java:129)
    at org.hibernate.engine.jdbc.internal.proxy.AbstractProxyHandler.invoke(AbstractProxyHandler.java:81)
    at com.sun.proxy.$Proxy54.executeQuery(Unknown Source)
    at org.hibernate.loader.Loader.getResultSet(Loader.java:1962)
    at org.hibernate.loader.Loader.doQuery(Loader.java:829)
    at org.hibernate.loader.Loader.doQueryAndInitializeNonLazyCollections(Loader.java:289)
    at org.hibernate.loader.Loader.doList(Loader.java:2447)
    at org.hibernate.loader.Loader.doList(Loader.java:2433)
    at org.hibernate.loader.Loader.listIgnoreQueryCache(Loader.java:2263)
    at org.hibernate.loader.Loader.list(Loader.java:2258)
    at org.hibernate.loader.hql.QueryLoader.list(QueryLoader.java:470)
    at org.hibernate.hql.internal.ast.QueryTranslatorImpl.list(QueryTranslatorImpl.java:355)
    at org.hibernate.engine.query.spi.HQLQueryPlan.performList(HQLQueryPlan.java:196)
    at org.hibernate.internal.SessionImpl.list(SessionImpl.java:1161)
    at org.hibernate.internal.QueryImpl.list(QueryImpl.java:101)
    at org.hibernate.ejb.QueryImpl.getSingleResult(QueryImpl.java:280)
    ... 12 more
Caused by: com.mysql.jdbc.exceptions.jdbc4.MySQLSyntaxErrorException: You have an error in your SQL syntax; check the manual that corresponds to your MySQL server version for the right syntax to use near '2 registered0_.id as id0_, registered0_.current_status as current2_0_, registere' at line 1
    at sun.reflect.NativeConstructorAccessorImpl.newInstance0(Native Method)
    at sun.reflect.NativeConstructorAccessorImpl.newInstance(Unknown Source)
    at sun.reflect.DelegatingConstructorAccessorImpl.newInstance(Unknown Source)
    at java.lang.reflect.Constructor.newInstance(Unknown Source)
    at com.mysql.jdbc.Util.handleNewInstance(Util.java:411)
    at com.mysql.jdbc.Util.getInstance(Util.java:386)
    at com.mysql.jdbc.SQLError.createSQLException(SQLError.java:1052)
    at com.mysql.jdbc.MysqlIO.checkErrorPacket(MysqlIO.java:3609)
    at com.mysql.jdbc.MysqlIO.checkErrorPacket(MysqlIO.java:3541)
    at com.mysql.jdbc.MysqlIO.sendCommand(MysqlIO.java:2002)
    at com.mysql.jdbc.MysqlIO.sqlQueryDirect(MysqlIO.java:2163)
    at com.mysql.jdbc.ConnectionImpl.execSQL(ConnectionImpl.java:2624)
    at com.mysql.jdbc.PreparedStatement.executeInternal(PreparedStatement.java:2127)
    at com.mysql.jdbc.PreparedStatement.executeQuery(PreparedStatement.java:2293)
    at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
    at sun.reflect.NativeMethodAccessorImpl.invoke(Unknown Source)
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(Unknown Source)
    at java.lang.reflect.Method.invoke(Unknown Source)
    at org.hibernate.engine.jdbc.internal.proxy.AbstractStatementProxyHandler.continueInvocation(AbstractStatementProxyHandler.java:122)
    ... 27 more

Answer 1

JPA getSingleResult() or null

http://sysout.be/2011/03/09/why-you-should-never-use-getsingleresult-in-jpa/

http://www.objectdb.com/java/jpa/query/execute