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From "Andreas Korneliussen (JIRA)" <derby-...@db.apache.org>
Subject [jira] Updated: (DERBY-1277) Call to rs.isLast() may cause rs.getXXX() return values from the last row instead of the current row in scrollable resultsets
Date Fri, 05 May 2006 16:04:28 GMT
     [ http://issues.apache.org/jira/browse/DERBY-1277?page=all ]

Andreas Korneliussen updated DERBY-1277:
----------------------------------------

     Summary: Call to rs.isLast() may cause rs.getXXX() return values from the last row instead
of the current row in scrollable resultsets  (was: Call to rs.isLast() may cause rs.getXXX()
return values from the last row instead of the current row in scrollable updatable resultsets)
     Version: 10.1.2.1
    Priority: Major  (was: Minor)

After analyzing this bug, I found that it is caused by TableScanResultSet and EmbedResultSet
sharing DataValueColumn descriptors, and that the call to isLast() will make TableScanResultSet
modify the data.

This bug was first only detected in updatable resultset, because they will have use TableScanResultSet
as source, while read-only resultsets use BulkTableScanResultSet as source.  

If the select statement contains "FOR UPDATE", also read-only scrollable resultsets will use
a TableScanResultSet as source. 

The bug is reproducable in Derby 10.1.2, ie. by modifying the select statement to contain
"FOR UPDATE", and open the resultset with concurrency CONCUR_READ_ONLY.

I will upload a patch, were ScrollInsensitiveResultSet is modified so that it will give a
reference to data which is in the hashtable.



> Call to rs.isLast() may cause rs.getXXX() return values from the last row instead of
the current row in scrollable resultsets
> -----------------------------------------------------------------------------------------------------------------------------
>
>          Key: DERBY-1277
>          URL: http://issues.apache.org/jira/browse/DERBY-1277
>      Project: Derby
>         Type: Bug

>   Components: SQL
>     Versions: 10.2.0.0, 10.1.2.1
>     Reporter: Andreas Korneliussen
>     Assignee: Andreas Korneliussen

>
> In scrollable updatable resultset, a call to rs.isLast() may cause rs.getXXX() return
values from the last row, instead of for the current row.  This may be related to the fact
that on calls to isLast() the scroll insensitive resultset moves to the last row, and then
moves back to the current row (see DERBY-1276 for related information). The call to isLast()
seems to have a sideeffect when the resultset is updatable.
> I have test which does the following:
>         Statement stmt1 = con.createStatement(ResultSet.TYPE_SCROLL_INSENSITIVE,ResultSet.CONCUR_UPDATABLE);
>         ResultSet rs = stmt1.executeQuery("select * from testRelative");
>         
>         rs.next(); // First Record
>         System.out.println("First record is: " + rs.getString("name"));
>         rs.relative(2); // Third Record        
>         System.out.println("Third record is: " + rs.getString("name"));
>         System.out.println(" isLast=" + rs.isLast());
>         System.out.println("Third record is: " + rs.getString("name"));
> The output is:
> First record is: work1
> Third record is: work3
>  isLast=false
> Third record is: work4
> isLast()==false
> The issue may also be reproduced by applying the following patch to testRelative:
> Index: java/testing/org/apache/derbyTesting/functionTests/tests/jdbcapi/testRelative.java
> ===================================================================
> --- java/testing/org/apache/derbyTesting/functionTests/tests/jdbcapi/testRelative.java
 (revision 399224)
> +++ java/testing/org/apache/derbyTesting/functionTests/tests/jdbcapi/testRelative.java
 (working copy)
> @@ -60,7 +60,7 @@
>                         pStmt.executeBatch();
>                         con.commit();
> -                       stmt1 = con.createStatement(ResultSet.TYPE_SCROLL_INSENSITIVE,ResultSet.CONCUR_READ_ONLY);
> +                       stmt1 = con.createStatement(ResultSet.TYPE_SCROLL_INSENSITIVE,ResultSet.CONCUR_UPDATABLE);
>                         rs = stmt1.executeQuery("select * from testRelative");
>                         rs.next(); // First Record

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