[Qgis-developer] OGR Buffer fails in Processing

[Even Rouault]

On jeudi 2 mars 2017 23:34:17 CET Paolo Cavallini wrote:
> Hi all,
> a simple buffer fails if applied to a PostGIS layer:
> ===
> Algorithm Buffer vectors starting...
> GDAL command:
> ogr2ogr
> "/tmp/processingf5bab9b07d834e229b9dd70899b8face/971076e5d374495280a95f7adf2
> ec92a/OUTPUTLAYER.shp" "PG:dbname='corso' host=localhost port=5432
> user='utente'
> password='utente' sslmode=disable" public.fiumi -dialect sqlite -sql
> "SELECT ST_Buffer( geometry , 100 ),* FROM 'public.fiumi' "
> GDAL command output:
> Warning 1: layer names ignored in combination with -sql.
> ERROR 1: In ExecuteSQL(): sqlite3_prepare(SELECT ST_Buffer( geometry ,
> 100 ),* FROM 'public.fiumi' ):
> no such column: geometry

--> Just guessing blindly. I guess that the "'geometry" column name in ST_Buffer(geometry, 
X) must be hardcoded in processing. This is the name of the geometry column used by 
default for OGR sources that have no explicit geometry column (like shapefiles). But when 
the source is a database, "geometry" must be replaced by the actual geometry column name 
from the database. Typically the one you get with OGR_L_GetGeometryColumn().

Pseudo code :

src_geometry_column =  OGR_L_GetGeometryColumn(layer)
if src_geometry_column is null or empty :
     sqlite_geometry_column = 'geometry'
else
     sqlite_geometry_column = src_geometry_column

Note: in the above case, the processing is a bit suboptimal as the source is PostGIS. Removing 
-dialect sqlite would speed up things and allow the buffering to be done by PostGIS itself.

> Converting outputs
> Caricamento layer
> 
> The following layers were not correctly generated.
> Buffer
> You can check the log messages to find more information about the
> execution of the algorithm
> ===
> Whereas it runs fine when applied to a shapefile.
> All the best.


-- 
Spatialys - Geospatial professional services
http://www.spatialys.com
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