Yep,
There is hooks on the clientdataset and the TProvider to pass specialised
information between the client and the Provider. See
TProvider.OnDataRequest, OnGetDataSetProperties. Never said it was simple.
Myles.
> -----Original Message-----
> From: Carl Reynolds [SMTP:[EMAIL PROTECTED]]
> Sent: Wednesday, September 08, 1999 5:10 PM
> To: Multiple recipients of list delphi
> Subject: RE: [DUG]: Efficient searching in TClientDataSet
>
> [Myles wrote]
> >Are the fields on which the locate is done Indexed (at either the client
> or
> >server end)??
> >
> >If you are using the briefcase model, is suspect it will have to load all
> >the records - an index may help.
>
> The locate fields are only indexed at the server end inasmuch as they're
> the result of a query with an order-by clause, and I don't have any client
> end indexing (or rather if I do all the records must be brought down
> anyway).
>
> Looking at TClientDataSet.LocateRecord, I'm not sure an index would help,
> as it seems to call CheckProviderEOF regardless (which loads down
> everything).
>
> >You could perhaps do some advanced fudging of the IProvider interface -
> >depends on what data requests are sent from the client to the server.
>
> Sounds hard. :) I settled for mucking about with
> TClientDataSet.LocateRecord, see below...
>
> [Yanbo wrote]
> >I have asked the similar question before, unfortuantely none answered it.
>
> >
> >In my project, when I do a Locate, I pass the Locate( a record number or
> a >range string) params to the middleware, the middle checks the params
> and >prepares a subset of the dataset( normally 1 ~ 100 records) for the
> client >application.
> >
> >When I started my n-tier prototype, I used the same method as yours.
> >Navigation is very slow.
>
> Latest developments
> I changed the code in TClientDataSet.LocateRecord as follows:
>
> begin
> CheckBrowseMode;
> CursorPosChanged;
> // CheckProviderEOF; // Don't want to bring all the data down
> Buffer := TempBuffer;
> Fields := TList.Create;
> ...
> Status := FLookupCursor.GetRecordForKey(FieldCount, PartialLength,
> Buffer, Buffer);
> if SyncCursor then begin
> while (Status <> DBIERR_NONE) and not ProviderEOF and
> FetchOnDemand and (PacketRecords <> 0) do begin
> FetchMoreData(false);
> Status :=
> FLookupCursor.GetRecordForKey(FieldCount, PartialLength, Buffer, Buffer);
> end;
> end;
> ...
>
> Basically, every time I search and fail I download another packet. Not
> exactly what I wanted, as I'm relying _heavily_ on GetRecordForKey being
> efficient, but it does seem to be a lot faster than stepping through
> record by record. And, unlike the normal locate, I'm only downloading
> packets until I reach the record I want.
>
> Any perceived flaws or suggested improvements?
>
> Cheers,
>
> Carl Reynolds Ph: +64-9-4154790
> CJN Technologies Ltd. Fax: +64-9-4154791
> [EMAIL PROTECTED] DDI: +64-9-4154795
> PO Box 302-278, North Harbour, Auckland, New Zealand
> 12 Piermark Drive, North Harbour Estate, Auckland, NZ
> Visit our website at http://www.cjntech.co.nz/
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