[fdo-trac] #309: Add two additional IFeatureReader properties: Count and IsEmpty

[FDO]

#309: Add two additional IFeatureReader properties: Count and IsEmpty
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 Reporter:  MaksimS      |         Owner:  gregboone
     Type:  enhancement  |        Status:  new      
 Priority:  minor        |     Milestone:  3.4.0    
Component:  FDO API      |       Version:  3.2.0    
 Severity:  3            |    Resolution:           
 Keywords:               |   External_id:           
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Comment (by MaksimS):

 Count would '''not''' get calculated on IFeatureReader instantiation (i.e.
 via ISelect.Execute). The property would act as a function, when
 explicitly called (get). If called, it should create an internal copy of
 underlying reader, traversing it to return total number of feature
 instances. If it's not calculated on IFeatureReader instantiation then
 there're no performance side effects. A private member could be used for
 storing once-calculated features count for faster consequent calls to
 Count() function of the same instance of IFeatureReader.

 Now, why IsEmpty when there's a Count? Because IsEmpty traverses only the
 first record of possibly many records, returning False if ReadNext doesn't
 return Nothing. IsEmpty() works on the same premises as above described
 Count() mechanism.

 So user can chain calls to get the results with less overhead:

 {{{
 If Not reader.IsEmpty
    Dim cnt As Integer = reader.Count
 ...
 End If
 }}}

 I think that it's better to have it implemented on unmanaged tier, since
 doing it using managed bindings may sometimes lead to unexpected results.

-- 
Ticket URL: <http://trac.osgeo.org/fdo/ticket/309#comment:1>
FDO <http://fdo.osgeo.org/>
Feature Data Objects