[Qgis-developer] feedback from today's course: various problems

Giovanni Manghi giovanni.manghi at gmail.com
Wed Dec 2 16:30:22 EST 2009

> - apparently it is not possible to merge two polygons when one of them has
> an island

With shapefiles (in qgis?) is not possible, as in not possible merging
non overlapping or non adjacent polygons.

This merge operations are possible with postgis and spatialite layers. 

But here the strange thing: I actually noticed that with postgis and
spatialite layers (type multipolygon) I cannot merge adjacent or
overlapping polygons... 

the message is:

"The union operation would result in a geometry type that is not
compatible with the current layer and therefore is canceled"

the same message when you try to merge non overlapping or non adjacent
polygons (or with islands) in shapefiles.

Moreover in trunk -buth not in 1.3- when I merge in postgis two non
adjacent polygons, after toggling editing I obtain the following

"ERROR:  duplicate key value violates unique constraint "regions_pkey""

and then

"Could not commit changes to layer regions
Errors: ERROR: 1 feature(s) not added.
SUCCESS: 2 feature(s) deleted."

If the same is done on a spatialite layer only the latter message is
shown (again, only in trunk, not in 1.3).

To test I used the layer "regions" you can find into the spatialite
sample dataset and the layer "world borders" you can find googling the

Seems to me something is wrong, let me know if you want me to file a


-- Giovanni --

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