[fdo-internals] Counting rows in managed IFeatureReader

[Barbara Zoladek]

Maksim,
Adding Count to IFeatureReader will have performance side effects. There is no way to find out the number of rows without either fetching all the rows or explicitly executing something like 'select count(*)' .

Robert's suggestion looks better.

Thanks,
Barbara.

-----Original Message-----
From: fdo-internals-bounces at lists.osgeo.org [mailto:fdo-internals-bounces at lists.osgeo.org] On Behalf Of Maksim Sestic
Sent: Thursday, April 17, 2008 2:56 AM
To: fdo-internals at lists.osgeo.org
Subject: RE: [fdo-internals] Counting rows in managed IFeatureReader


Thanks for the tip, Robert. I need to use ISelect because of locking (which
is not supported by ISelectAggregates).

I'd suggest that generic IFeatureReader (neverthless of provider involved)
expose two additional readonly properties:

1) Count - creates internal copy of a reader and traverses it, returning
total number of feature instances found in it.

2) IsEmpty - boolean returning True if reader has no features instances in
it, False otherwise.

Regards,
Maksim Sestic



Robert Fortin wrote:
>
> Maksim,
>
> You can use the IselectAggregate command with the COUNT function to
> retrieve the number of rows for a given class.
> This will ensure that you use the optimize implementation of the native
> data source to retrieve the number of row where it is available.
>
> Robert Fortin
>
> -----Original Message-----
> From: fdo-internals-bounces at lists.osgeo.org
> [mailto:fdo-internals-bounces at lists.osgeo.org] On Behalf Of Maksim Sestic
> Sent: Wednesday, April 16, 2008 6:11 AM
> To: fdo-internals at lists.osgeo.org
> Subject: [fdo-internals] Counting rows in managed IFeatureReader
>
>
> Hi all,
>
> Since IFeatureReader doesn't provide Count property for total number of
> records in it, what's the most "proper" way to get it out from managed
> IFeatureReader? I'm asking this because of necessity to explicitly close a
> reder after it's returned from, say, ISelect command. How do I get a safe
> copy of instantiated managed IFeatureReader object to count it's
> properties,
> without affecting the original one?
>
> It would be a no brainer if IFeatureReader was fully implemented in .NET,
> but managed bindings always make me wonder if unmanaged resources get
> disposed in a proper way.
>
> Regards,
> Maksim Sestic
> --
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