[fpc-pascal] How to detect supported data types in dataset?

Reinier Olislagers reinierolislagers at gmail.com
Thu Sep 8 05:42:55 CEST 2011

Hi list,

Possible newbie question so feel free to educate me ;)
(Away for some days, so may not read response until back)

A patch by Ludo Brands on bufdataset (mantis 19930) got me thinking:

  ftSupported = [ftString,ftGuid,... and so on];

procedure TCustomBufDataset.CreateDataset;
var i:integer;
// check if all types are supported
  For i:=0 to FieldDefs.Count-1 do
    if not (Fielddefs.items[i].DataType in ftSupported) then


Suppose I want to write a dataset data copier or importer/exporter, how
do I detect supported datatypes in a dataset?

For example, in my dbfexport test code, I make a bufdataset with all
possible fields, then strip each field away when strange errors/AVs
occur when assigning values to them.
For other datasets (with similar checks as proposed in Ludo's patch),
the runtime library is nice enough to warn me on field creation that it
doesn't work.

Am I missing something obvious or does it make sense to expose something
like a SupportedFieldTypes property for datasets?
How does Delphi do this?

Besides that, I think it's an excellent idea to check for invalid
datatypes when creating fields, rather than failing later on when
assigning values to them.
(Of course, if that is implemented in a lot of datasets, checking
exceptions when creating fields would be a rough way of checking if a
datatype is supported ;)

I understand that 3rd party inherited datasets may not abide by this,
but it's worth a shot to offer the functionality..


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