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From "Daniel John Debrunner (JIRA)" <j...@apache.org>
Subject [jira] Updated: (DERBY-1998) JDBC 4 isWrapper() and unWrap() methods allow unwrapping to Derby implementation classes.
Date Wed, 04 Jul 2007 15:47:04 GMT

     [ https://issues.apache.org/jira/browse/DERBY-1998?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel

Daniel John Debrunner updated DERBY-1998:

    Priority: Major  (was: Critical)

I think there's a slight difference between these two.

EmbedStatement es = (EmbedStatement) stmt;

EmbedStatement es = stmt.unwrap(EmbedStatement.class);

The first is just how Java works.

The second is Derby's driver api indicating that the returned statement objcet is a wrapper
for EmbedStatement.
That is not guaranteed by Derby either in a current release or in any future release, e.g.
the object used to implement java.sql.Statement could change in the next release, even on
a branch. So there is a very minor chance that an application could come to rely on it since
its information obtained from Derby's driver.

I'll drop this to major, I think that some of the changes suggested are good, just relying
on interfaces. 

Maybe something like

for Derby objects that implement Statement.

ireturn clazz == java.sql.Statement.class;

for Derby objects that implement PreparedStatement.

return  clazz == java.sql.Statement.class || clazz == java.sql.PreparedStatement.class

I agree it would be good to get EmbedStatement and other similar objects not to be public.

> JDBC 4 isWrapper() and unWrap() methods allow unwrapping to Derby implementation classes.
> -----------------------------------------------------------------------------------------
>                 Key: DERBY-1998
>                 URL: https://issues.apache.org/jira/browse/DERBY-1998
>             Project: Derby
>          Issue Type: Bug
>          Components: JDBC
>            Reporter: Daniel John Debrunner
> I do not believe that the unwrapping mechanism of JDBC 4 should allow or encourage unwrapping
a JDBC 4 object as one of Derby's pribvate implementation types.
> Since Derby does *not* wrap objects in any way I would say there is a stong case for
saying that the isWrapper() method should always return false and the unWrap() method always
throw an exception.
> For example in EmbedStatement40 this code will allow "unwrapping" to
>    EmbedStatement40, EmbedStatement, EngineStatement, ConnectionChild, Object, Statement
>    public boolean isWrapperFor(Class<?> interfaces) throws SQLException {
>         checkStatus();
>         return interfaces.isInstance(this);
>     }
>     public <T> T unwrap(java.lang.Class<T> interfaces)
>     throws SQLException{
>         checkStatus();
>         try {
>             return interfaces.cast(this);
>         } catch (ClassCastException cce) {
>             throw newSQLException(SQLState.UNABLE_TO_UNWRAP,interfaces);
>         }
>     }

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