[postgis-devel] Promote Geometry to MultiGeometry on Insert

[Even Rouault]

Le 17/02/2023 à 20:28, Regina Obe a écrit :
>
> Would that be a breaking change for any down the stream apps. Suddenly 
> mixing multi with singles?
>
> That would be my main concern.
>
Yes that would be. Typically GeoPackage has the same strong/pedantic 
typing constraints as PostGIS on geometry columns. So a "ogr2ogr 
out.gpkg PG:...." scenario would currently break if a PostGIS 
multipolygon layer would contain polygons (well, to be more exact, the 
GPKG driver would actually accept a mix of polygons & multipolygons in a 
multipolygon layer, but would emit a warning that this is non conformant 
to the GPKG spec)

GML has also different types for single vs multi.

Shapefile is a bit weird, where it has the same type for 
Polygon/MultiPolygon and LineString/MultiLineString, but distinguishes 
Point from MultiPoint...

I agree with Darafei that, in an ideal world, a punctual / linear / 
areal separation, that would encompass single vs multi, "straight" vs 
"curvy" variants, would make much more sense. If you could know for a 
geometry colum of type "linear", if it actually contains rows with 
single, multi, straight or curvy, that could make the translation to 
other formats easier, but I guess that would involve triggers to keep 
such metadata up-to-date. Changing the whole ecosystem of formats is tricky.

PostGIS being lax on ingestion and automatically converting single to 
multipart however is non breaking.

-- 
http://www.spatialys.com
My software is free, but my time generally not.
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