OGR ODBC spatial query has invalid resultset

[Frank Warmerdam]

Delfos, Jacob wrote:
> Hi List,
> 
> Sorry about all the questions I have been sending. I'm hoping someone 
> can shed light on this one.
> 
> After a QueryByPoint or QueryByRect operation in PHP, the number of 
> results is correct, but the resultCacheMemberObj always points to the 
> first "getNumResults()" objects. If there are 4 results, it holds 
> references to objects 1-4. For one result, it always points to the 1st 
> object.
> 
> This is -not- the case for QueryByAttributes, though. The 
> resultCacheMemberObj is correct for this type of query.
> 
> This only occurs for OGR ODBC layers. I have tried MDB and CSV, with the 
> same problem…
> 
> If anyone knows why, please let me know. If someone thinks this is a 
> bug, I'll file it.

Jacob,

This occurs with OGR ODBC datasources that lack an FID column in the original
table.  Without an FID, OGR just assigns FIDs starting with zero to the
result set.

The problem really bites when different constraints (spatial or attribute)
are in place at the point where the query is done, and when the results are
fetched - which is the case when you do spatial queries as the spatial query
apparently is cleared by mapserver before it starts fetching individual
results.

The overall point is that two-stage queries (as done by mapserver) are
very unreliable against OGR datasources without a persistent FID, such as
some ODBC datasources.

BTW, you can use the mapserver config variable ODBC_OGR_FID to force the
ODBC driver to pick a particular column as the FID.  Unfortunately this
is a global option so it only works smoothly if you have the same name
for the id of all tables you are accessing in a given mapserver map.  You
would add something like the following in the MAP section of your map file
to default to using the ID column of your odbc tables as the feature id.

   CONFIG "ODBC_OGR_FID" "ID"

Best regards,
-- 
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I set the clouds in motion - turn up   | Frank Warmerdam, warmerdam at pobox.com
light and sound - activate the windows | http://pobox.com/~warmerdam
and watch the world go round - Rush    | President OSGeo, http://osgeo.org