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From "Knut Anders Hatlen (JIRA)" <j...@apache.org>
Subject [jira] Commented: (DERBY-4062) Method override missing from DataValueFactory interface
Date Wed, 18 Feb 2009 10:39:01 GMT

    [ https://issues.apache.org/jira/browse/DERBY-4062?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12674567#action_12674567
] 

Knut Anders Hatlen commented on DERBY-4062:
-------------------------------------------

I find this change confusing too. I'd say we should either remove all the methods without
a previous parameter, or we should keep all of them. The existence of a catch-all method (getDataValue(Object))
that silently returns another data type than expected makes it too risky to have the mix that
we have now, in my opinion.

If we follow the pattern of the 540791 commit, we should replace calls to dvf.getDataValue()
without a previous argument with a direct call to the constructor of the data type we want.
So we would change

  row.setColumn(SYSXPLAIN_RESULTSET_NO_OPENS, dvf.getDataValue(no_opens));

to

  row.setColumn(SYSXPLAIN_RESULTSET_NO_OPENS, new SQLInteger(no_opens));

I see that that's what many other row factories do as well, and in some ways I think it's
easier to read as you immediately see what's the intended data type for that column. And the
SQL* classes are in the same iapi package as the DataValueFactory interface, so it's not like
we're exposing implementation details by making such a change.

> Method override missing from DataValueFactory interface
> -------------------------------------------------------
>
>                 Key: DERBY-4062
>                 URL: https://issues.apache.org/jira/browse/DERBY-4062
>             Project: Derby
>          Issue Type: Sub-task
>            Reporter: Bryan Pendleton
>            Assignee: Bryan Pendleton
>            Priority: Minor
>         Attachments: addToInterface.diff
>
>
> I believe the problem involves o.a.d.iapi.types.DataValueFactory.
> This interface defines dozens and dozens of overloads of the method
> getDataValue(), for lots of different combinations of datatypes.
> For most of the Java "boxed" types (Short, Long, Float, Double, etc.),
> DataValueFactory defines a pair of getDataValue() methods. For example,
> here are the method pair that the interface defines for Short:
>         /**
>          * Get a SQL smallint with the given value.  A null argument means get
>          * a SQL null value.  The second form uses the previous value (if non-null)
>          * to hold the return value.
>          *
>          */
>         NumberDataValue         getDataValue(Short value);
>         NumberDataValue         getDataValue(Short value, NumberDataValue previous)
>                                                         throws StandardException;
> HOWEVER, for the Integer type, DataValueFactory doesn't define both overloads,
> but only defines the 'previous'-style overload:
>         /**
>          * Get a SQL int with the given value.  A null argument means get
>          * a SQL null value.  Uses the previous value (if non-null)
>          * to hold the return value.
>          *
>          */
>         NumberDataValue         getDataValue(Integer value, NumberDataValue previous)
>                                                         throws StandardException;
> The actual implementation, in o.a.d.iapi.types.DataValueFactoryImpl, though,
> does implement both the Integer overloads. But this method is NOT present
> in the DataValueFactory interface:
>         NumberDataValue         getDataValue(Integer value);
>  Because this method is not present in the interface, code such as
>    row.setColumn(SYSXPLAIN_RESULTSET_NO_OPENS, dvf.getDataValue(no_opens));
> which the code anticipates will invoke the above method, instead calls the method
>    public UserDataValue getDataValue(Object value); 
> which has a very different behavior (instead of returning a SQLInteger, it returns a
UserType).
> This accidental invocation of the wrong implementation method was causing data corruption
> errors in regression tests for the DERBY-2487 patch, which uses the above setColumn call.
> Instead of inserting SQLInteger values into the system table, the code was inserting
> java.lang.Integer UserType values; since those values don't match the defined type of
> the column(s) in the system catalog, the table appeared to be corrupt.
> I believe that this problem never affects external Derby applications, but only internal
Derby code,
> as the DataValueFactory interface is an internal interface only. Still, since it appeared
to
> cause data corruption and invalid query results, it is potentially a quite serious problem.
> See this thread in the derby-dev archives for a bit more discussion:
> http://mail-archives.apache.org/mod_mbox/db-derby-dev/200902.mbox/%3C4997818E.3080007@amberpoint.com%3E

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