[Gambas-user] isNull()

[Benoît Minisini]

> On Thu, 25 Nov 2010 10:01:42 am Benoît Minisini wrote:
> > > I use IsNull extensively, is that going to be removed?
> > > 
> > > richard
> > 
> > No. I use it extensively too.
> > 
> > Here is the result of my thought:
> > 
> > - You can know the datatype of a variant with the TypeOf() function. You
> > don't have to use the current IsXXXX() functions.
> > 
> > - But you often need to know if a string can be converted to a number, an
> > integer, a float, a date.
> > 
> > - You normally want to know that for localized strings get from the
> > outside (i.e. the user). For non-localized strings, they are intern to
> > your program, so you should know what you are doing.
> > 
> > So:
> > 	IsNull(x) -> kept its behaviour.
> > 	IsInteger(x) -> If Val(x) returns an integer
> > 	IsFloat(x) -> If Val(x) returns a float
> > 	IsDate(x) -> If Val(x) returns a date
> > 
> > They should be enough. But I could add:
> > 	IsLong(x) -> If Val(x) returns a Long
> > 	IsSingle(x) -> If Single(x) returns a Single.
> > 
> > Regards,
> 
> Benoît,
> 
> I would like to see the generic IsNumber retained.  When dealing with
> external data sources, i.e. data from an external system source not "a
> user" the content of data fields in a database can vary widely over time.
> In different eras, a particular column may have it's type changed in the
> source database system but the existent data remains undisturbed.
> 
> Although it sounds weird, we often see data columns on mainframe and even
> on some PC based rdbms that have gone from a text (or char or varchar) to
> a numeric type, to a different numeric type and so forth.  In these
> database systems, any new inserts or updates will conform to the current
> type definition.  However, existing data is left as is.
> 
> So if "booktype" was originally char(1), then became charvar then became a
> specific structured datatype (for example, some of the custom types
> provided for in postgresql), we still see instances of, say "A" being
> returned by the dbms for booktype.  (The way we handle this is by way of
> our own postgresql "front end" database that accesses the remote dbms and
> returns text fields for any and all columns that contain suspect data
> types.)
> 
> In the main, I don't care if the field contains an integer or a float (or a
> long or single etc) just that it contains a number and not any non-numeric
> data.  I will worry about the representation after I have determined that
> it is a number.
> 
> I realise that this is a fairly arcane use of gambas, but the speed that we
> can develop (and run) filters based on this approach is why I chose gambas
> in the first place.  As I said, we use a 80-20 rule to get to the core
> issue of the data as soon as possible.  The parsing filters get more and
> more complex for each 20% left over.   So the ability to recognise
> "generic" datatypes in string values, "is it a number, good, then return
> true else start looking for other clues as to what it is supposed to
> represent ... does it look like it might be a date? If so then try to
> decipher the date structure, else does it look like a "known" construct
> (i.e IF wkstr LIKE "*(*%)*" then ...) etc etc.
> 
> 
> Oh, and by the way, I too use IsNull extensively, specifically to provide
> "lazy loads" of subordinate persisted objects, usually collections, whose
> content is not required unless specifically accessed.  For example, a
> "Book" object may have a property which is an "Author" object.  When the
> persisted book object is loaded from the database, the author object is
> not loaded until the program actually accesses the book.author property,
> viz
> 
> PRIVATE FUNCTION MyAuthor() as Author
> 	if IsNull($myAuthor)
> 		$myAuthor=NEW Author
> 		$myAuthor.LoadDB(ME.AuthorName)
> 	endif
> 	RETURN $myAuthor
> END
> 
> (obviously simplified to exclude error checking).

You must check the datatype of a column by using Result.Fields["xxx"].Type, 
not by using IsXXXX() on the value. 

Or if really you don't want, use TypeOf().

Anyway, in my list, IsFloat() does what you want IsNumber() to do, as there is 
no number higher than Float in the Gambas number hierarchy.

Regards,

-- 
Benoît Minisini