#30020: Support reading null values for numeric fields on Shapefile import via
LayerMapping
-------------------------------------+-------------------------------------
Reporter: Kathryn | Owner: nobody
Killebrew |
Type: New | Status: new
feature |
Component: GIS | Version:
Severity: Normal | Keywords: GIS, GEOS,
Triage Stage: | LayerMapping
Unreviewed | Has patch: 0
Needs documentation: 0 | Needs tests: 0
Patch needs improvement: 0 | Easy pickings: 0
UI/UX: 0 |
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On reading a Shapefile into a model object via `LayerMapping`, set numeric
field value to `None` instead of zero if the model field is nullable and
input field value is either null or unset. Currently, both nulls and
zeroes in the input are stored as zeroes.
Shapefiles do not officially support storing nulls:
http://resources.esri.com/help/9.3/ArcGISDesktop/com/Gp_ToolRef/geoprocessing_tool_reference/geoprocessing_considerations_for_shapefile_output.htm
However, on inspecting the DBF contents via `ogrinfo` with GDAL 2.1 or
2.2, both zeroes and nulls display, so some unofficial support exists.
GDAL 2.2 added support for distinguishing between "unset" fields and those
explicitly set to null:
https://trac.osgeo.org/gdal/wiki/rfc67_nullfieldvalues
Adding null support should be possible by either checking before casting
the value with OGR `IsFieldSetAndNotNull` on GDAL 2.2+ or checking with
OGR `IsFieldSet` on older GDAL versions:
https://www.gdal.org/classOGRFeature.html#a260b925400b72914eb1b8cc9a3bf4029
--
Ticket URL: <https://code.djangoproject.com/ticket/30020>
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