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Posted to derby-user@db.apache.org by Tim Dudgeon <td...@informaticsmatters.com> on 2014/01/06 13:47:09 UTC

varargs functions: primitive or Object type?

I'm trying to write a function that performs aggregation and I'm not 
clear on how to handle the varargs part.
Lets assume I was wanting to write a function that does averaging, and 
handles null values correctly.
I'm defining my function like this:

CREATE FUNCTION MYAVG
( VALS DOUBLE ... )
RETURNS DOUBLE
PARAMETER STYLE DERBY
NO SQL LANGUAGE JAVA
EXTERNAL NAME 'myorg.misc.derby.functions.MyFunctions.myAverage;


What does the signature of the Java method need to be?
I've tried:

static Double myAverage(Double[] vals) { }
static Double myAverage(Double... vals) { }

Both of these fail with:
java.sql.SQLSyntaxErrorException: No method was found that matched the 
method call myorg.misc.derby.functions.MyFunctions.myAverage(double...), 
tried all combinations of object and primitive types and any possible 
type conversion for any  parameters the method call may have

Seems like its wanting
static Double myAverage(double... vals) { }
but if that's the case how are nulls handled?

Thanks
Tim

Re: varargs functions: primitive or Object type?

Posted by Tim Dudgeon <td...@informaticsmatters.com>.

On 06/01/2014 15:34, Rick Hillegas wrote:
> Maybe your problem is that your methods are not public.

Damn it your right. That one method was not public!
Sorry :-(

Tim

Re: varargs functions: primitive or Object type?

Posted by Rick Hillegas <ri...@oracle.com>.
On 1/6/14 6:09 AM, Rick Hillegas wrote:
> On 1/6/14 4:47 AM, Tim Dudgeon wrote:
>> I'm trying to write a function that performs aggregation and I'm not 
>> clear on how to handle the varargs part.
>> Lets assume I was wanting to write a function that does averaging, 
>> and handles null values correctly.
>> I'm defining my function like this:
>>
>> CREATE FUNCTION MYAVG
>> ( VALS DOUBLE ... )
>> RETURNS DOUBLE
>> PARAMETER STYLE DERBY
>> NO SQL LANGUAGE JAVA
>> EXTERNAL NAME 'myorg.misc.derby.functions.MyFunctions.myAverage;
>>
>>
>> What does the signature of the Java method need to be?
>> I've tried:
>>
>> static Double myAverage(Double[] vals) { }
>> static Double myAverage(Double... vals) { }
>>
>> Both of these fail with:
>> java.sql.SQLSyntaxErrorException: No method was found that matched 
>> the method call 
>> myorg.misc.derby.functions.MyFunctions.myAverage(double...), tried 
>> all combinations of object and primitive types and any possible type 
>> conversion for any  parameters the method call may have
>>
>> Seems like its wanting
>> static Double myAverage(double... vals) { }
>> but if that's the case how are nulls handled?
>>
>> Thanks
>> Tim
>>
>>
>>
> Thanks for tripping across this, Tim. Looks like there's a bug in 
> here. Works for Integer args but not Double args. Stand by while I 
> take a look...
>
> Thanks,
> -Rick
>
Hi Tim,

Well, I'm puzzled. Now I can't reproduce the problem I thought I was 
seeing. I have written a script which tests all possible datatypes with 
varargs. The script runs cleanly. The following small test case works 
too. Compile the following class...

public class ww
{
     public  static  Double doubleAverage( Double... vals )
     {
         double result = 0;

         for ( Double val : vals )
         {
             result += val.doubleValue();
         }

         return result / vals.length;
     }
}

...then the following script runs cleanly for me...

connect 'jdbc:derby:memory:db;create=true';

create function doubleAverage( vals double... ) returns double
language java parameter style derby no sql
external name 'ww.doubleAverage';

values doubleAverage( 1.11, 2.22, 3.33 );

values doubleAverage( 1.0, 2.0, 3.0 );

Maybe your problem is that your methods are not public.

By the way: If your ultimate problem is an aggregation problem, you may 
be interested in the user defined aggregates feature which was 
introduced by release 10.10.1: 
http://db.apache.org/derby/docs/10.10/devguide/cdevspecialuda.html

Hope this helps,
-Rick

Re: varargs functions: primitive or Object type?

Posted by Rick Hillegas <ri...@oracle.com>.
On 1/6/14 4:47 AM, Tim Dudgeon wrote:
> I'm trying to write a function that performs aggregation and I'm not 
> clear on how to handle the varargs part.
> Lets assume I was wanting to write a function that does averaging, and 
> handles null values correctly.
> I'm defining my function like this:
>
> CREATE FUNCTION MYAVG
> ( VALS DOUBLE ... )
> RETURNS DOUBLE
> PARAMETER STYLE DERBY
> NO SQL LANGUAGE JAVA
> EXTERNAL NAME 'myorg.misc.derby.functions.MyFunctions.myAverage;
>
>
> What does the signature of the Java method need to be?
> I've tried:
>
> static Double myAverage(Double[] vals) { }
> static Double myAverage(Double... vals) { }
>
> Both of these fail with:
> java.sql.SQLSyntaxErrorException: No method was found that matched the 
> method call 
> myorg.misc.derby.functions.MyFunctions.myAverage(double...), tried all 
> combinations of object and primitive types and any possible type 
> conversion for any  parameters the method call may have
>
> Seems like its wanting
> static Double myAverage(double... vals) { }
> but if that's the case how are nulls handled?
>
> Thanks
> Tim
>
>
>
Thanks for tripping across this, Tim. Looks like there's a bug in here. 
Works for Integer args but not Double args. Stand by while I take a look...

Thanks,
-Rick