Pat,
the reason I am looking to test for 'Null' is I have a utility
utl_Is_Empty(->Var_or_Field) --> boolean
This utility returns true if the field or var is 'empty', if the value
is a default empty value for the field or var type (i.e. text = "").
However, as I mentioned before, something that occurred to me (I have
not run into it, personally, yet) was that it is possible that a field
(it appears a var is never null), could be Null.
The code for utl_is_empty did not check for that situation. I was
expecting a there to be a simple command, like Nil() for a pointer, a
pointer and get a boolean answer, and there is although the command is
not as simple as "Null(->Field-or_var)", the command is 'Is field value
Null', and it is a simple command that returns a boolean. However, in
my code since I am dealing blindly with a pointer to... something... I
have to do a bit more testing.
Since utl_is_Empty requires a pointer the following few lines of code
were/are needed
RESOLVE POINTER($Object_ptr;$Varname;$Table;$Field)
If ($Field>0) //this is a field
$Is_Empty:=(Is field value Null($Object->))
End if
On Sun, 3 Jun 2018 13:40:44 +0100, Pat Bensky via 4D_Tech wrote:
> Maybe try something like this:
> - Set an error handler
> - Try to use that field or variable
> - If it is null then the error handler will catch it
>
> eg:
> ON ERR CALL("errorcatcher")
> $result:=$BooleanVarOrfield=true
> ON ERR CALL("")
>
> On 2 June 2018 at 15:02, Arnaud de Montard via 4D_Tech <4d_tech@lists.4d.com
>> wrote:
>
>>
>>> Le 1 juin 2018 à 20:39, Chip Scheide via 4D_Tech <4d_tech@lists.4d.com>
>> a écrit :
>>>
>>> I meant - I was looking for a command which behaved like Nil(), but for
>>> Null.
>>
>> Hi Chip,
>> I had a bad recent experience with a legacy db in which check box "convert
>> Null to empty" was sometimes on, sometimes off… The use of QUERY command,
>> in that situation, is risky:
>> //example with date
>> QUERY($table_p->;$field_p->=!00/00/0000!)
>> $empty_l:= Records in selection($table_p->)
>> QUERY($table_p->;$field_p->#!00/00/0000!)
>> $notEmpty_l:= Records in selection($table_p->)
>> ASSERT(Records in table($table_p->)=($empty_l+$notEmpty_l);"data
>> integrity or bad Null setting")
>>
>> It's checked everywhere now.
>>
>> In a brand new DB, and *knowing what strategy has been adopted about Null
>> use*, things could be different.
>>
>> --
>> Arnaud de Montard
>>
>>
>>
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>
>
>
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