[Mondrian] CurrentDateMember udf

[Rushan Chen]

If expanding the UDF interface to use Mondrian exp cache is not 
recommended, I will try to cache this locally(inside the UDF), so that 
the user of this UDF does not have to worry about caching.

Rushan

Julian Hyde wrote:
>  
>
>   
>> The caching I was thinking of adding does use the dependency 
>> interface 
>> to declare that CurrentDateMember/CurrentDateString UDFs are not 
>> dependent on any dimension value.
>>     
>
> I don't think 'interface UserDefinedFunction' has a method for declaring
> dependencies. Nor should it have, because dependencies are difficult to mere
> mortals to understand.
>
>   
>> I will add the timestamp to RolapResult because it will make any 
>> computation requiring the current time consistent. However, 
>> itself alone 
>> will not help with the time consuming part of the UDF, i.e. issuing a 
>> SQL to look up whether the member value corresponding the (cached) 
>> timestamp string exists. Expression caching will still be a good 
>> addition here.
>>     
>
> If CurrentDateMember cannot declare its dependencies - and it can't because
> it's a UDF - expression caching will be ineffective. You should either cache
> within the function, or add this new Cache() function which knows to ignore
> dependencies and force caching.
>
> Julian
>
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