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<p class=MsoNormal><span style='font-size:10.0pt;font-family:"Verdana","sans-serif";
color:#003399'>Dear OGR devs,<o:p></o:p></span></p>
<p class=MsoNormal><span style='font-size:10.0pt;font-family:"Verdana","sans-serif";
color:#003399'><o:p> </o:p></span></p>
<p class=MsoNormal><span style='font-size:10.0pt;font-family:"Verdana","sans-serif";
color:#003399'>OGRLayer::TestCapability allows you to determine if an OGRLayer
supports various things, such as creating new features or updating or deleting existing
features. Can you advise me whether there are any drivers for which the capabilities
differ for a given layer depending on whether it is instantiated as an OGRLayer
via OGRDataSource::GetLayer vs. OGRDataSource::ExecuteSQL? Also, whether the
capabilities will change after OGRLayer::SetAttributeFilter or OGRLayer::SetSpatialFilter
is called on the resulting OGRLayer instance?<o:p></o:p></span></p>
<p class=MsoNormal><span style='font-size:10.0pt;font-family:"Verdana","sans-serif";
color:#003399'> <o:p></o:p></span></p>
<p class=MsoNormal><span style='font-size:10.0pt;font-family:"Verdana","sans-serif";
color:#003399'>In my scenario, I occasionally need to open layers using the
equivalent of a SQL WHERE and/or ORDER BY clauses. WHERE can be achieved by either
including the expression in a call to OGRDataSource::ExecuteSQL, or by calling OGRDataSource::GetLayer
and then OGRLayer::SetAttributeFilter on the resulting instance. ORDER BY can
be only achieved via OGRDataSource::ExecuteSQL (please correct me if I'm wrong
here). Basically, I would like to know if the following approach is a robust
way of checking capabilities:<o:p></o:p></span></p>
<p class=MsoNormal><span style='font-size:10.0pt;font-family:"Verdana","sans-serif";
color:#003399'> <o:p></o:p></span></p>
<p class=MsoListParagraph style='text-indent:-.25in;mso-list:l0 level1 lfo1'><![if !supportLists]><span
style='font-size:10.0pt;font-family:"Verdana","sans-serif";color:#003399'><span
style='mso-list:Ignore'>1.<span style='font:7.0pt "Times New Roman"'>
</span></span></span><![endif]><span style='font-size:10.0pt;font-family:"Verdana","sans-serif";
color:#003399'>Call OGRDataSource::GetLayer and then OGRLayer::TestCapability
to determine what capabilities are supported for that layer.<o:p></o:p></span></p>
<p class=MsoListParagraph><span style='font-size:10.0pt;font-family:"Verdana","sans-serif";
color:#003399'><o:p> </o:p></span></p>
<p class=MsoListParagraph style='text-indent:-.25in;mso-list:l0 level1 lfo1'><![if !supportLists]><span
style='font-size:10.0pt;font-family:"Verdana","sans-serif";color:#003399'><span
style='mso-list:Ignore'>2.<span style='font:7.0pt "Times New Roman"'>
</span></span></span><![endif]><span style='font-size:10.0pt;font-family:"Verdana","sans-serif";
color:#003399'>Sometime later, call either OGRDataSource::ExecuteSQL or OGRDataSource::GetLayer
again (possibly followed by OGRLayer::SetAttributeFilter and/or OGRLayer::SetSpatialFilter),
depending on whether ORDER BY or WHERE are ultimately required for the specific
situation.<o:p></o:p></span></p>
<p class=MsoNormal><span style='font-size:10.0pt;font-family:"Verdana","sans-serif";
color:#003399'> <o:p></o:p></span></p>
<p class=MsoNormal><span style='font-size:10.0pt;font-family:"Verdana","sans-serif";
color:#003399'>I would like to know if the capabilities that were tested in
step #1 will remain true in step #2, or if OGRLayer::TestCapability must be
called after the final OGRLayer is instantiated and OGRLayer::SetAttributeFilter
and/or OGRLayer::SetSpatialFilter have been called, just prior to accessing the
features.<o:p></o:p></span></p>
<p class=MsoNormal><span style='font-size:10.0pt;font-family:"Verdana","sans-serif";
color:#003399'><o:p> </o:p></span></p>
<p class=MsoNormal><span style='font-size:10.0pt;font-family:"Verdana","sans-serif";
color:#003399'>(As a side issue, I realize that the approach above is imperfect
in other aspects, e.g. it is not optimal, and another thread could conceivably
change the layer between step #1 and #2, but I'm not concerned about those
issues in my scenario and would like to use this approach for various reasons.
Thus, suggestions for how I can moot my question by changing my approach will
not work for me.)<o:p></o:p></span></p>
<p class=MsoNormal><span style='font-size:10.0pt;font-family:"Verdana","sans-serif";
color:#003399'><o:p> </o:p></span></p>
<p class=MsoNormal><span style='font-size:10.0pt;font-family:"Verdana","sans-serif";
color:#003399'>Thanks for your help with this esoteric question,<o:p></o:p></span></p>
<p class=MsoNormal><span style='font-size:10.0pt;font-family:"Verdana","sans-serif";
color:#003399'><o:p> </o:p></span></p>
<p class=MsoNormal><span style='font-size:10.0pt;font-family:"Verdana","sans-serif";
color:#003399'>Jason<o:p></o:p></span></p>
<p class=MsoNormal><span style='font-size:10.0pt;font-family:"Verdana","sans-serif";
color:#003399'><o:p> </o:p></span></p>
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