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From "Bryan Pendleton (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (DERBY-5872) Inconsistency between isWrapperFor() and unwrap() in logical statements
Date Sat, 21 Jul 2012 17:44:34 GMT

    [ https://issues.apache.org/jira/browse/DERBY-5872?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13419891#comment-13419891
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Bryan Pendleton commented on DERBY-5872:
----------------------------------------

Looks quite thorough and complete. Thanks for cleaning this up; I'm always pleased
to see patches that remove redundant code!

I'm not that familiar with java.sql.Wrapper. It is a JDBC4/JDK6 feature, is that right?

I tried to look back through svn history to figure out when these wrapper methods were
introduced, and it looks like it was at least 5 years ago. It's interesting that nobody
encountered these problems until now; I suppose this means that the Wrapper
interface isn't heavily used?

Regardless, thanks again for cleaning up the implementation and adding the extra tests.
                
> Inconsistency between isWrapperFor() and unwrap() in logical statements
> -----------------------------------------------------------------------
>
>                 Key: DERBY-5872
>                 URL: https://issues.apache.org/jira/browse/DERBY-5872
>             Project: Derby
>          Issue Type: Bug
>          Components: JDBC
>    Affects Versions: 10.4.1.3, 10.5.1.1, 10.6.1.0, 10.7.1.1, 10.8.1.2, 10.9.1.0
>            Reporter: Knut Anders Hatlen
>            Assignee: Knut Anders Hatlen
>         Attachments: derby-5872-1a.diff
>
>
> I noticed this when I refactored the logical statement classes in DERBY-5868. The isWrapperFor()
method forwards calls to the underlying physical statement, but the unwrap() method works
purely at the logical level.
> For example, if you produce a LogicalPreparedStatement40 instance with this code
>         ClientConnectionPoolDataSource ds = new ClientConnectionPoolDataSource();
>         ds.setDatabaseName("testdb");
>         ds.setCreateDatabase("create");
>         ds.setMaxStatements(10);
>         PooledConnection pc = ds.getPooledConnection();
>         Connection c = pc.getConnection();
>         PreparedStatement ps = c.prepareStatement("values 1");
> you'll see that
>         System.out.println(ps.isWrapperFor(LogicalPreparedStatement40.class));
> prints false, telling that ps is not a wrapper for LogicalPreparedStatement40. However,
trying to unwrap ps as a LogicalPreparedStatement succeeds:
>         LogicalPreparedStatement40 lps = ps.unwrap(LogicalPreparedStatement40.class);
> On the other hand
>         System.out.println(ps.isWrapperFor(PreparedStatement40.class));
> prints true, indicating that ps is a wrapper for PreparedStatement40, but trying to unwrap
it as one, fails:
>         PreparedStatement40 ps4 = ps.unwrap(PreparedStatement40.class);
> Exception in thread "main" java.sql.SQLException: Unable to unwrap for 'class org.apache.derby.client.am.PreparedStatement40'
> 	at org.apache.derby.client.am.SQLExceptionFactory40.getSQLException(SQLExceptionFactory40.java:108)
> 	at org.apache.derby.client.am.SqlException.getSQLException(SqlException.java:364)
> 	at org.apache.derby.client.am.LogicalStatementEntity.unwrap(LogicalStatementEntity.java:258)
> 	at org.apache.derby.client.am.LogicalPreparedStatement.unwrap(LogicalPreparedStatement.java:57)
> 	at Test.main(Test.java:37)
> Caused by: org.apache.derby.client.am.SqlException: Unable to unwrap for 'class org.apache.derby.client.am.PreparedStatement40'
> 	... 3 more

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