Checking for null date

[Ruslan Zasukhin]

On 3/29/09 9:58 PM, "Steve Albin" <steve at steve-albin.com> wrote:

>>> I'm using V4RB 4 and I need to know how to tell if a date field in a cursor
>>> is
>>> null.  
>>> 
>>> I tried this:
>>> 
>>>   if VDateTime(cursor.Field(27)).Value <> nil then
>>>     Return  VDateTime(cursor.Field(27)).Value
>>>   else
>>>     Return nil
>>>   end
>>>  
>>> This returns a date field, but an invalid date which I would expect since I
>>> know the field is <NULL>.
>>> 
>>> I tried this:
>>> 
>>>   if  self.cursor.Field(27).GetString <> "" then
>>>     Return  VDateTime(cursor.Field(27)).Value
>>>   else
>>>     Return nil
>>>   end
>>>     
>>> This returns nil as expected.
>>> 
>>> I can easily change my code to check the string value, but it seems that the
>>> first way should work.  What am I doing wrong?
>> 
>> Much more easy
>> 
>>    if curs.Field(27).IsNull
> 
> That is easier.  Thanks!
> 
> But, the question was why doesn't VDateTime(cursor.Field(27)).Value return
> nil.  Is is becasue casting the date causes a date field to be created with
> unpredictable results?  This is probably an RB question more than a Valentina
> question...

No,

This is because WE did not promise you this !! :-)

Valentina PATTERN of work with NULL and value is:

  IF you know that you have NULLABLE field THEN
    
    * you MUST at first check
            fld.IsNull()        <<< this read ONE BIT from bitset file

    * then only if not NULL, you can touch
            fld.Value           <<<< reads from VALUE file,
                                this can be many bytes ...


-- 
Best regards,

Ruslan Zasukhin
VP Engineering and New Technology
Paradigma Software, Inc

Valentina - Joining Worlds of Information
http://www.paradigmasoft.com

[I feel the need: the need for speed]