VRT driver does not implement GetFIDColumn()

[kyngchaos]

The VRT driver does not implement the GetFIDColumn() method for cases when the <FID> tag is used to specify a source attribute to use as FID.

[warmerdam]

William,

This is not an actionable bug report.

If I'm in autotest/ogr and issue the following command I see FID's reported by ogrinfo through the VRT driver based on the FID column.

warmerdam@gdal:~/gdal/autotest/ogr$ ogrinfo data/vrt_test.vrt test4
INFO: Open of `data/vrt_test.vrt'
      using driver `VRT' successful.

Layer name: test4
Geometry: Point
Feature Count: 2
Extent: (12.500000, 17.000000) - (100.000000, 200.000000)
Layer SRS WKT:
(unknown)
fid: Integer (8.0)
other: String (8.0)
x: Real (8.3)
y: Real (8.3)
z: Real (8.3)
wkt: String (30.0)
OGRFeature(test4):1
  fid (Integer) = 1
  other (String) = First
  x (Real) =   12.500
  y (Real) =   17.000
  z (Real) =    1.200
  wkt (String) = POINT(12.5 17 1.2)
  POINT (12.5 17.0 1.2)

OGRFeature(test4):2
  fid (Integer) = 2
  other (String) = Second
  x (Real) =  100.000
  y (Real) =  200.000
  z (Real) =    0.000
  wkt (String) = POINT(100 200 0)
  POINT (100 200 0)

So obviously there is something specific about your problem that you are going to have to support.

[Even Rouault]

Well, William meant that the *name* of the FID column is not reported. See ​http://lists.osgeo.org/pipermail/gdal-dev/2012-April/032584.html

[warmerdam]

Subject and text updated accordingly.

Note that I suspect the result of a VRT does not have to have all the attributes of the source and so the FID column from the source might not actually appear in the virtual layer. In such a case GetFIDColumn() should *not* return the name.

[Even Rouault]

r24311 /trunk/ (4 files in 3 dirs): VRT: implement GetFIDColumn() (#4637)

Frank, I agree with your restriction that the "FID column from the source might not actually appear in the virtual layer. In such a case GetFIDColumn() should *not* return the name". But actually that's not always respected by other drivers.

For example, see the PG driver where the FID column is 'hidden' in the regular fields, but exposed at the FID column by GetFIDColumn(). But in that situation, what is reported by the GetFIDColumn() can be queried with ExecuteSQL() (as it is directly interpreted by the PG driver engine.

$ ogrinfo pg:dbname=autotest poly -so -al
INFO: Open of `pg:dbname=autotest'
      using driver `PostgreSQL' successful.

Layer name: poly
Geometry: Multi Polygon
Feature Count: 9
Extent: (478315.531250, 4762880.500000) - (481645.312500, 4765610.500000)
Layer SRS WKT:
(unknown)
FID Column = ogc_fid
Geometry Column = wkb_geometry
area: Real (12.3)
eas_id: Real (0.0)
prfedea: String (16.0)

But that's a bit of the particular case, and I haven't tried to address that.