Jon,
this is a bug on the result SQL layer implementation of GetFeature().
Can you file a ticket in https://github.com/OSGeo/gdal/issues/new with
the below elements? Thanks
Even
Le 22/06/2022 à 15:37, Jon Morris a écrit :
Hello all,
I’m having trouble getting features in a layer after sorting with SQL
query. It seems that the FIDs change when the layer is sorted. I’m ok
with that, but if you take the id returned by GetFID and call
GetFeature on the layer, you get a different feature. I would have
thought GetFID/GetFeature should remain in sync even after sorting.
The docs for GetFeature say “If this method returns a non-NULL
feature, it is guaranteed that its feature id (OGRFeature::GetFID())
will be the same as nFID.“
https://gdal.org/doxygen/classOGRLayer.html#ace902dfb44335fb1a877aa035ecff209
I’m aware I could just iterate through the layer, but I want to
add/delete features so prefer to iterate through a list of ids
instead. Should I just ignore the FIDs and iterate through
range(layer.GetFeatureCount()) instead? Is that guaranteed to give me
every feature in size order?
I’m using GDAL 3.4.1 on Python 3.8.12
Repro case:
https://gist.github.com/jontwo/01d8cbf1e047e36d2fb2f7786ad60e73
Creates a layer with 4 features, areas 1, 64, 4, 25
Then sorts them with ds.ExecuteSQL(f"SELECT * FROM lname ORDER BY
OGR_GEOM_AREA ASC")
Gets a list of FIDs in the layer using GetFID
Calls GetFeature for each of these FIDs.
Output:
Areas before: [(0, 1.0), (1, 64.0), (2, 4.0), (3, 25.0)]
Areas after: [(0, 1.0), (2, 4.0), (3, 25.0), (1, 64.0)]
Requested FID 0 (area 1.0) got 0 (area 1.0)
Requested FID 2 (area 4.0) got 3 (area 25.0)
Requested FID 3 (area 25.0) got 1 (area 64.0)
Requested FID 1 (area 64.0) got 2 (area 4.0)
Thanks,
Jon
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