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Option to add GDAL/OGR Feature Id field to LAYER attributes#7533

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rouault merged 5 commits into
MapServer:mainfrom
geographika:ogr-fid
Jun 23, 2026
Merged

Option to add GDAL/OGR Feature Id field to LAYER attributes#7533
rouault merged 5 commits into
MapServer:mainfrom
geographika:ogr-fid

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@geographika

@geographika geographika commented Jun 19, 2026

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Both GDAL and QGIS show the FID column when opening through GDAL. For example the fid column below:

gdal info .\buildings.gpkg
INFO: Open of `.\buildings.gpkg'
      using driver `GPKG' successful.
Layer name: buildings
Geometry: Multi Polygon
...
FID Column = fid
Geometry Column = geom
osm_id: String (0.0)
name: String (0.0)
building: String (0.0)

MapServer however does not make this field available as an attribute. For example:

LAYER
  NAME "buildings"
  # interestingly adding fid below also makes the field available, but the "all" option cannot then be used
  # PROCESSING "ITEMS=fid,building"
  # new PROCESSING  keyword added in this pull request
  PROCESSING "OGR_EXPOSE_FID=TRUE"
  CONNECTIONTYPE OGR
  CONNECTION "data/osm/timisoara/buildings.gpkg"
  METADATA
    "ows_title" "Buildings"
    "gml_include_items" "all"
    "gml_featureid" "fid"
    "gml_types" "auto"
    "oga_queryable_items" "all"
END

Without the changes in this pull request a query such as http://localhost:7000//timisoara/ogcapi/collections/buildings/items?f=json

will return the following error (as "gml_featureid" "fid" is not found):

{"code":"ServerError","description":"Error getting feature. Feature id not found."}

With the new PROCESSING "OGR_EXPOSE_FID=TRUE" the FID is now available, and can be used as the unique Id field, as labels, expressions etc.

I'm not a fan of adding more and more processing keywords, but adding the FID by default breaks 100s of tests, and therefore possibly live MapServer deployments.

As I understand it FID columns in OGR are always 64-bit integers, so "Long" can be set as the default type.

I had a look through the code and I don't think there is an existing way to add these feature Ids so they are available to MapServer apart from manually adding the field name in PROCESSING "ITEMS=fid,building" as shown in the example above.

rouault
rouault reviewed Jun 20, 2026
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I'd like to see an added test with a WFS FILTER query on the fid field to make sure no other code path needs to be updated

Comment thread src/mapogr.cpp Outdated
geographika and others added 2 commits June 20, 2026 10:27
@geographika @rouault
Update src/mapogr.cpp
376afcf 
Co-authored-by: Even Rouault <even.rouault@spatialys.com>
@geographika
Add FID tests
476b887
@geographika

geographika commented Jun 20, 2026

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WFS filter tests added, which highlight a few things.

  • WFS supports FeatureId queries without having to have the "fid" exposed. See the test with &REQUEST=GetFeature&TYPENAMES=popplace_gpkg_nofid&FILTER=<fes:Filter+xmlns:fes='http://www.opengis.net/fes/2.0'><fes:ResourceId+rid='popplace_gpkg_nofid.1'/></fes:Filter>"
  • However the wfs_featureid needs to be set in the metadata or the following error is returned <!-- WARNING: No featureid defined for typename 'popplace_gpkg_nofid'. Output will not validate. -->.
  • Adding PROCESSING "OGR_EXPOSE_FID=TRUE" will expose the fid as a standard property, but the GML Ids are also in the output.

When using OGC Features API, the fid needs to be available so it can be added to the queryables and sortables. My use case that highlighted this was an OSM export where the osm_id is not unique, but GDAL reports there is a unique fid, but it is not usable by MapServer. Obviously a workaround is to add a new field, but it seems as though MapServer should be as similar as possible to GDAL (and QGIS).

@rouault rouault merged commit a53a187 into MapServer:main Jun 23, 2026
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@rouault rouault added this to the 8.8.0 Release milestone Jun 23, 2026
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