[Mapserver-dev] Re: OGR Layers

[Frank Warmerdam]

Daniel Morissette wrote:
> I can see why it could be nice to have OGR perform the filter sometimes, 
> but I'm not very comfortable with using FILTERITEM to control that.  Do 
> you know if any of the other data sources (PostGIS, SDE, Oracle) support 
> this way of passing down the filter and how they do it?  We should 
> probably implement things the same way in OGR as in the PostGIS/SDE 
> drivers.
> 
> I'm a bit worried that we would create confusion if the expression was 
> handled differently when FILTERITEM isn't set.  AFAIK everywhere else in 
> MapServer the FILTERITEM/CLASSITEM/etc is optional when you use logical 
> expressions (it is ignored) and then MapServer scans the expression 
> itself to find the fields that it needs to read.  With that change, OGR 
> would become an exception to this and I'm worried that someone could set 
> or unset FILTERITEM by accident and then would not understand why their 
> expression doesn't work the same way as before.  (Until they go and read 
> the docs of course but that shouldn't be required in a consistent system.)
> 
> I'll forward this to mapserver-dev to see what Steve and others think.

Daniel,

My understanding is that the FILTER clause is interpreted as the contents
of a WHERE clause and FILTERITEM is unused for the database layer types
(Oracle, PostGIS).  So my intent was to make the OGR layer similar to these,
at least if FILTERITEM is not defined.  However, I agree that it could be
confusing to have behaviour so different if FILTERITEM happened to be
forgotten by accident.

Best regards,

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