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From "Bryan Pendleton (JIRA)" <j...@apache.org>
Subject [jira] Updated: (DERBY-4062) Remove single-argument getDataValue overrides from DataValueFactory interface
Date Wed, 06 May 2009 17:50:30 GMT

     [ https://issues.apache.org/jira/browse/DERBY-4062?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
]

Bryan Pendleton updated DERBY-4062:
-----------------------------------

    Attachment: removeSingleArgOverrides.diff

Knut, thanks for the feedback. You're right, that was a typo in my previous comment,
I had meant to suggest the alternative of switching to the 2-argument getDataValue() call.

But I also feel that the 4th alternative, the one which directly invokes the SQLtype constructor,
is the cleanest, so I went ahead with a prototype of this approach.

Attached is removeSingleArgOverrides.diff, a patch proposal. I think it's appealing
because not only does it remove the core problem that this issue is concerned with
(ambiguity in method overriding in the DataValueFactory interface), but it also does
so by deleting code (which is good), and by making the code more self-evident, I think.

For example, consider this bit from SYSCONGLOMERATESRowFactory.java:

The current code says:

                /* 3rd column is CONGLOMERATENUMBER (long) */
                row.setColumn(3, dvf.getDataValue(conglomNumber));

The new code says:
                /* 3rd column is CONGLOMERATENUMBER (long) */
                row.setColumn(3, new SQLLongint(conglomNumber));

I think that the new code is clearer.

Please have a look at the patch and let me know what you think.


> Remove single-argument getDataValue overrides 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, getDataValueCalls.out, removeSingleArgOverrides.diff
>
>
> [ Issue title edited to reflect the discussion about how to clarify the use of this interface.
]
> 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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