[fpc-devel] TClientDataset (was: Dnamic packages support)

[Joost van der Sluis]

Op zondag 04-11-2007 om 00:34 uur [tijdzone +0100], schreef Michael Van
Canneyt:
> 
> On Sat, 3 Nov 2007, Joost van der Sluis wrote:
> 
> > Op zaterdag 03-11-2007 om 19:57 uur [tijdzone +0100], schreef Michael
> > Van Canneyt:
> > > 
> > > Packages and the missing TClientDataset are the only 2 remaining
> > > things 
> > > stopping me from using FPC/Lazarus for my daytime job. All else is 
> > > covered or can be covered with a minimal amount of work. 
> > 
> > You'll have to explain the TClientDataset to me. Do you need a
> > symantical identical equivalent of TClientDataset?
> 
> I need all features offered by TClientDataset:
> 
> - 3-tier database handling, TProvider and all.
> - Local filtering
> - Local sorting/indexing
> - Locate()
> - Maintained Aggregates
> - Load/Save to file (briefcase model)
> 
> And all features are critical; We have about 3200 instances in 1 application,
> almost all of them using all of the features mentioned, maybe with exception
> of the aggregates.
> 
> > Or do you only miss some features in sqldb?
> 
> SQLDB will be good for our server tier, so I can drop the IBX.
> But it's not suitable for the client layer.
> 
> As I see it, TClientDataset should be built on top of TBufDataset.
> Local filtering is available as fas as I know (or did you put it 
> in TSQLQuery ?), and the indexing probably also can somehow be 
> managed. The locate can be done with a filter. The maintained
> aggregates would need to be implemented from scratch, as well
> as the packet handling and file handling...

Local filtering is in TBufDataset, locate also. The packet-handling is
also there?
Only no file-handling. But that's more because I didn't find it urgent
enough to implement. It should be very easy. And there are no local
indexes. 

Bu I know where to work on now. But there's also a design-issue.

You talked about a TProvider. But as TBufdataset is setup know, you
don't need any. For every kind of connection between TBufDataset and the
ouside world, you'll have to use another descendent of TBufDataset.

So we can add a TProviderDataset or something, that can connect to data
on an application-server. Is this ok to you? That way you always heve to
re-create your descendent of TBufDataset for every connection?

Or do you like the TClientDataset model better? So that you can connect
it to any TProvider you want - to get access to some data?

You're right that we could make a TClientDataset which inherits from
TBufDataset. But that kind of defeats the purpose of TBufDataset.
Because if you do so, it would also be better to base TSQLQuery on
TDataset directly. Or else you're double-buffering your data when you
connect a TSQLQuery (TBufDataset) with a TProvider to a TClientDataset
(another TBufDataset).

Joost