Thanks Peter (and Myles) for your help, but I guess you're trying to
solve a different problem. The full story is quite a mouthful, so I've
held back from explaining my setup so far - I guess I should go into
more detail.
Without delving too deeply into why, I have a "listbox" of "customers"
and an associated "grid" of "orders", and in some cases the orders grid
might display all, or almost all, orders for ALL customers. I realise
that this is not often desirable, but it's up to the user. The user
does have the option of filtering on the data at any point, but there
are valid cases for them wanting to see everything.
So, it's a single tier setup, but ClientDataSets are used as they have a
lot of useful functionality - for example, constructing indexes on the
fly so that the data in the grid can be ordered by calculated fields -
click on a column and it orders by that column, that sort of thing. In
addition, when a query with a very large result set is executed, using a
ClientDataSet makes navigating "nicer" in look and feel - once a certain
set of records is loaded, browsing among that set is very quick, as
opposed to browsing against a query, where paging up a page is just as
slow as paging down. This is even without discussing maintenance
issues.
It's this last case, where we have a large result set of all orders for
all customers, which interests me. In this case, we want to accept the
default ordering of orders grouped by customers. The user always has
the option of loading in all the records into the ClientDataSet, eg. by
dragging the scrollbar on the grid down to the bottom, but under some
circumstances this might cause quite a wait. More likely, the user
might wish to move down to view the orders of a particular customer.
It's this moving down in the grid which I'm trying to do as economically
as possible - cache the records for all customers down to the customer
clicked on, and no more. Unfortunately, the behaviour of
ClientDataSet.Locate is to immediately fetch all the records into its
cache and then to do a search on the appropriate fields. And moving
through the clientdataset record by record, until you find the record
you want, is very slow indeed. So I ended up modifying
ClientDataSet.LocateRecord, as discussed in my last email, and now it
does do what I want. The code's not perfect (mainly because I fear what
GetRecordForKey might actually be doing behind the scenes!) but I
haven't found a better solution yet and tests so far have worked quite
well.
What you suggested, and what Myles suggested before you, are totally
valid if you're doing things in a three tier situation. In that case
you'd want to avoid the situation that I've described anyway - you would
try to insist on quite a stringent filter being applied before ever
loading down any records to the client. Performance between the middle
tier and the database would dwindle into insignificance compared to the
considerations of data transfer over your WAN. So I appreciate your
sensible advice, and I don't wish to seem ungrateful, I just didn't
explain myself properly! :)
Anyway, enough rambling (deep breath :).
Incidently, should discussions of Queries and ClientDataSets really be
under DUG-DB? Or is that just SQL related stuff?
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/
> -----Original Message-----
> From: Peter G Jones [SMTP:[EMAIL PROTECTED]]
> Sent: Friday, September 10, 1999 8:42 PM
> To: Multiple recipients of list delphi
> Subject: Re: [DUG]: Efficient searching in TClientDataSet
>
> If you are using a cds locally (no server) then presumably you are
> doing a
> loadfromfile so you will always have all the records in memory. If
> not,
> then you should do your search on the server via the
> provider.datarequest.
>
>
> >From: Carl Reynolds <[EMAIL PROTECTED]>
> >Reply-To: [EMAIL PROTECTED]
> >To: Multiple recipients of list delphi <[EMAIL PROTECTED]>
> >Subject: [DUG]: Efficient searching in TClientDataSet
> >Date: Wed, 8 Sep 1999 13:02:32 +1200
> >
> >When I do a Locate on a TClientDataSet, it immediately loads all
> >remaining records into its buffer, ignoring PacketRecords. The same
> >thing happens when using FindKey or GotoKey. If I don't want to have
> >all the records loaded automatically (because I have a very large
> result
> >set), is there a more efficient way to locate a record than to step
> >through one record at a time, checking each for a match?
> >
> >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/
> ><< attach3 >>
>
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