Exception in thread "main" org.hibernate.QueryException: illegal attempt to dereference collection

今天在使用HQL查询时一直报错：

Exception in thread "main" org.hibernate.QueryException: illegal attempt to dereference collection [person0_.person_id.myEvent] with element property reference [title] [from com.mao.Person p where p.myEvent.title > :title]
	at org.hibernate.QueryException.generateQueryException(QueryException.java:137)
	at org.hibernate.QueryException.wrapWithQueryString(QueryException.java:120)
	at org.hibernate.hql.internal.ast.QueryTranslatorImpl.doCompile(QueryTranslatorImpl.java:234)
	at org.hibernate.hql.internal.ast.QueryTranslatorImpl.compile(QueryTranslatorImpl.java:158)
	at org.hibernate.engine.query.spi.HQLQueryPlan.(HQLQueryPlan.java:131)
	at org.hibernate.engine.query.spi.HQLQueryPlan.(HQLQueryPlan.java:93)
	at org.hibernate.engine.query.spi.QueryPlanCache.getHQLQueryPlan(QueryPlanCache.java:167)
	at org.hibernate.internal.AbstractSessionImpl.getHQLQueryPlan(AbstractSessionImpl.java:301)
	at org.hibernate.internal.AbstractSessionImpl.createQuery(AbstractSessionImpl.java:236)
	at org.hibernate.internal.SessionImpl.createQuery(SessionImpl.java:1836)
	at com.mao.join.HqlQuery.findPersons(HqlQuery.java:31)
	at com.mao.join.HqlQuery.main(HqlQuery.java:17)
Caused by: org.hibernate.QueryException: illegal attempt to dereference collection [person0_.person_id.myEvent] with element property reference [title]
	at org.hibernate.hql.internal.ast.tree.DotNode$1.buildIllegalCollectionDereferenceException(DotNode.java:73)
	at org.hibernate.hql.internal.ast.tree.DotNode.checkLhsIsNotCollection(DotNode.java:618)
	at org.hibernate.hql.internal.ast.tree.DotNode.resolve(DotNode.java:252)
	at org.hibernate.hql.internal.ast.tree.FromReferenceNode.resolve(FromReferenceNode.java:126)
	at org.hibernate.hql.internal.ast.tree.FromReferenceNode.resolve(FromReferenceNode.java:121)
	at org.hibernate.hql.internal.ast.HqlSqlWalker.resolve(HqlSqlWalker.java:959)
	at org.hibernate.hql.internal.antlr.HqlSqlBaseWalker.expr(HqlSqlBaseWalker.java:1267)
	at org.hibernate.hql.internal.antlr.HqlSqlBaseWalker.exprOrSubquery(HqlSqlBaseWalker.java:4686)
	at org.hibernate.hql.internal.antlr.HqlSqlBaseWalker.comparisonExpr(HqlSqlBaseWalker.java:4228)
	at org.hibernate.hql.internal.antlr.HqlSqlBaseWalker.logicalExpr(HqlSqlBaseWalker.java:2104)
	at org.hibernate.hql.internal.antlr.HqlSqlBaseWalker.whereClause(HqlSqlBaseWalker.java:796)
	at org.hibernate.hql.internal.antlr.HqlSqlBaseWalker.query(HqlSqlBaseWalker.java:597)
	at org.hibernate.hql.internal.antlr.HqlSqlBaseWalker.selectStatement(HqlSqlBaseWalker.java:301)
	at org.hibernate.hql.internal.antlr.HqlSqlBaseWalker.statement(HqlSqlBaseWalker.java:249)
	at org.hibernate.hql.internal.ast.QueryTranslatorImpl.analyze(QueryTranslatorImpl.java:278)
	at org.hibernate.hql.internal.ast.QueryTranslatorImpl.doCompile(QueryTranslatorImpl.java:206)
	... 9 more

相关HQL部分代码：

List pl = sess.createQuery("from Person p where p.myEvent.title > :title")
			// 执行setString()方法为HQL语句的参数赋值
			.setString("title", " ")
			//Query调用list()方法访问查询的全部实例
			.list();

报错原因：

在Hibernate3.2.3以前的版本中对所有的关联实体自动使用隐式连接。对于以下HQL语句：

List pl = sess.createQuery("from Person p where p.myEvent.title > :title")

无论如何Hibernate都会对p.myEvent.title自动使用隐式连接，所以以上HQL语句总是有效。

但是Hibernate3.2.2版本以后，Hibernate改变了默认的隐式策略，改为：（以上面的HQL语句为例）

1：如果myEvent是普通组件属性，或者单个的关联实体，则Hibernate会自动生成隐式内连接，也就是上面的HQL语句依然有效。

2：如果myEvent是一个集合，包括1—N、N-1关联，那么系统就会抛出

Exception in thread "main" org.hibernate.QueryException: illegal attempt to dereference collection异常

解决方案：

1：退回使用Hibernate3.2.3版本（当然不太推荐）

2：改为显示连接。

以上面的HQL为例改为：

String hql="from Person p inner join p.myEvent e where e.title > :title";

保存--->运行--->成功