Implement MakeValid() for non-column values.

[milosu]

PostGIS provides function ST_MakeValid, that can be used in Django as a PostGISOperator.

There is however no way how to use ST_MakeValid to simply repair GEOS Geometry.

Note that there is also no comparable function in the GEOS library itself (not counting something simple like buffer(0)).

This missing feature is also subject to Stackoverflow questions, like:
​https://stackoverflow.com/questions/45631855/equivalent-of-postgis-st-makevalid-in-django-geos/45633779

Attached patch implements new PostGISOperations method called "make_valid", that can be run from implementation code simply by:

from django.db import connection

repaired_geos_geometry = connection.ops.make_valid(some_goes_geometry)

[Mariusz Felisiak]

​MakeValid is already implemented.

[milosu]

St_MakeValid is implemented, but there is no way to call it on GEOS geometry.
See e.g.
​https://stackoverflow.com/questions/45631855/equivalent-of-postgis-st-makevalid-in-django-geos/45633779

[Simon Charette]

The MakeValid function also supports Geometry objects so you could theoretically do

valid_geometry = AModel.objects.annotate(
    valid_geometry=MakeValid(invalid_geometry),
).values_list('valid_geometry', flat=True).first()

But that assumes AModel has at least one row.

The ORM doesn't support SELECT from no tables by it's table <-> model class mapping nature.

If we wanted to add a way to do that it we should do it for all non-column referencing expressions and not only for MakeValid.

e.g.

• Expression.from_db() -> SELECT expression -> what's returned from the database.
• MakeValid(invalid_geometry).from_db('other') -> SELECT ST_MakeValid(<Geometry>) (from connections['other'])-> <Valid Geometry>
• Unaccent(Lower('ÉtÉ')).from_db() -> SELECT unaccent(lower('ÉtÉ')) -> 'ete'

This would have to be discussed on the developer mailing list and I wouldn't be surprised if there was existing tickets tracking this feature request.

[Mariusz Felisiak]

If you want to propose to add a new API for all non-column expressions (as described by Simon) then please fill a new ticket (I couldn't find an existing ticket) that would have to be discussed on the developer mailing list.

IMO, adding a special behavior only for MakeValid() is not something that we would like to add into Django.