[hibernate-issues] [Hibernate-JIRA] Created: (HHH-3056) Exception with empty resultset in HQL query containing join fetch of collection

[Tony Lin (JIRA)]

Exception with empty resultset in HQL query containing join fetch of collection
-------------------------------------------------------------------------------

                 Key: HHH-3056
                 URL: http://opensource.atlassian.com/projects/hibernate/browse/HHH-3056
             Project: Hibernate3
          Issue Type: Bug
          Components: query-hql
    Affects Versions: 3.2.5
         Environment: Windows XP sp2, Java 1.6.03, Tomcat 5.5.25
            Reporter: Tony Lin
         Attachments: object.zip

When performing this query on the attached model:

select subset from com.alphait.domain.snomed.object.SubsetImpl as subset join fetch subset.members as members left join fetch members.parent where subset.id = -1

We received the following exception:

org.hibernate.exception.GenericJDBCException: could not perform sequential read of results (forward)
        at org.hibernate.exception.SQLStateConverter.handledNonSpecificException(SQLStateConverter.java:103)
        at org.hibernate.exception.SQLStateConverter.convert(SQLStateConverter.java:91)
        at org.hibernate.exception.JDBCExceptionHelper.convert(JDBCExceptionHelper.java:43)
        at org.hibernate.loader.Loader.loadSequentialRowsForward(Loader.java:398)
        at org.hibernate.impl.FetchingScrollableResultsImpl.next(FetchingScrollableResultsImpl.java:55)
        at org.hibernate.impl.FetchingScrollableResultsImpl.first(FetchingScrollableResultsImpl.java:200)
...
Caused by: java.sql.SQLException: Illegal operation on empty result set.
        at com.mysql.jdbc.SQLError.createSQLException(SQLError.java:910)
        at com.mysql.jdbc.ResultSet.checkRowPos(ResultSet.java:713)
        at com.mysql.jdbc.ResultSet.getLong(ResultSet.java:2850)
        at com.mysql.jdbc.ResultSet.getLong(ResultSet.java:2845)
        at com.mysql.jdbc.ResultSet.getLong(ResultSet.java:2960)
        at org.hibernate.type.LongType.get(LongType.java:28)
        at org.hibernate.type.NullableType.nullSafeGet(NullableType.java:163)
        at org.hibernate.type.NullableType.nullSafeGet(NullableType.java:154)
        at org.hibernate.loader.Loader.getKeyFromResultSet(Loader.java:1097)
        at org.hibernate.loader.Loader.loadSequentialRowsForward(Loader.java:387)

After investigating the source code, we found two places are problematic:

1. org.hibernate.loader.Loader's loadSequentialRowsForward method:

			if (resultSet.isAfterLast() ) {
				// don't even bother trying to read further
				return null;
			}

			if (resultSet.isBeforeFirst() ) {
				resultSet.next();
			}

	Both isBeforeFirst(), and isAfterLast() returnd false if the resultset is empty, so the code after these statements are executed before next() is called. we added the following lines to fix this problem:

			if (resultSet.getRow() < 1) {
				return null;
			}
		
2. In org.hibernate.impl.FetchingScrollableResultsImpl's next() method, it aways returns true unless maxPosition is set. Should it be something like the following?

               Object row = getLoader().loadSequentialRowsForward(
				getResultSet(),
				getSession(),
				getQueryParameters(),
				false
		);

		if (row == null) {
			return false;
		}

     .....

We have not set scroll with other position yet.


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