[fdo-internals] resetting a feature reader

[Gavin Cramer]

How about, for the providers that have the internal functionality for an
optimised reset, making them smart enough to use it if a caller invokes
FdoISelect::Execute again with no changes to filters or other
attributes?  This doesn't have to be required behaviour, but just a
performance tweak that works whenever possible.
 
Gavin
 

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From: fdo-internals-bounces at lists.osgeo.org
[mailto:fdo-internals-bounces at lists.osgeo.org] On Behalf Of Badreddine
Karoui
Sent: Friday, January 26, 2007 2:11 PM
To: FDO Internals Mail List
Subject: RE: [fdo-internals] resetting a feature reader



It's too bad that we didn't make that an FDO command. In that case you
would use the capability to decide. Now you have to link against the
specific provider.

 

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From: fdo-internals-bounces at lists.osgeo.org
[mailto:fdo-internals-bounces at lists.osgeo.org] On Behalf Of Traian
Stanev
Sent: January 26, 2007 2:07 PM
To: FDO Internals Mail List
Subject: RE: [fdo-internals] resetting a feature reader

 

Yeah I did think about that, but in the context where I want to use this
(MapGuide rendering), I could be dealing with a feature reader from any
provider. I'd rather not split the code off into code paths that assume
certain providers, although I do realize that that's the alternative.

 

 

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From: fdo-internals-bounces at lists.osgeo.org
[mailto:fdo-internals-bounces at lists.osgeo.org] On Behalf Of Badreddine
Karoui
Sent: Friday, January 26, 2007 2:04 PM
To: FDO Internals Mail List
Subject: RE: [fdo-internals] resetting a feature reader

Train,

 

   Did you try the scrollable reader(ExtendedSelect). You can call
GetFirst and iterate through the reader again. Or you can call GetLast
and do that in reverse.

 

Badreddine

 

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From: fdo-internals-bounces at lists.osgeo.org
[mailto:fdo-internals-bounces at lists.osgeo.org] On Behalf Of Traian
Stanev
Sent: January 26, 2007 1:42 PM
To: FDO Internals Mail List
Subject: RE: [fdo-internals] resetting a feature reader

 

 

 

In the case of a spatial query (the most likely case), feature readers
for providers like SDF and SHP have a list of the feature IDs that match
the query. So the reader can be reset for free. I realize this is not
the case for all providers, but the lack of a reset means I have to pay
the select penalty for all providers even though I don't need to for
some.

 

 

 

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From: fdo-internals-bounces at lists.osgeo.org
[mailto:fdo-internals-bounces at lists.osgeo.org] On Behalf Of Orest
Halustchak
Sent: Friday, January 26, 2007 1:36 PM
To: FDO Internals Mail List
Subject: RE: [fdo-internals] resetting a feature reader

Hi,

 

Unless the provider internally has cached the results of the select or
provided some other tracking of the select results (e.g. as needed by
the new scrollable feature reader), the provider effectively would have
to re-execute the query anyway. So, I don't think you'd be saving
anything.

 

Thanks,

Orest.

 

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From: fdo-internals-bounces at lists.osgeo.org
[mailto:fdo-internals-bounces at lists.osgeo.org] On Behalf Of Traian
Stanev
Sent: Friday, January 26, 2007 12:23 PM
To: fdo-internals at lists.osgeo.org
Subject: [fdo-internals] resetting a feature reader

Hi,

 

How hard would it be to provide a Reset() capability for the
FdoIFeatureReader interface?

 

The example use for that would be for two-pass rendering of features.

I know that one could re-execute the Select command to get the same
reader, but this would in theory incur a higher penalty, since it would
have to redo a spatial query for example.

 

 

Traian

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