Aggregate Sum of GIS Aggregates fails

[Daniel Wiesmann]

There is an error when trying to compute a regular aggregate value from a GIS Area aggregate output. To take an example from the GIS geoapp tests, the following query fails.

from django.db.models import Sum
from django.contrib.gis.db.models.functions import Area

Country.objects.annotate(areasum=Sum(Area('mpoly')))

I tracked this down to the from_db_value function in the GeometryField class here:

​https://github.com/django/django/blob/master/django/contrib/gis/db/models/fields.py#L259

The problem seems to be that the Area function returns a float, but the field is expecting a value that can be converted to a Geometry.

I'll open a pull request with a regression test and a proposed solution.

[Tim Graham]

​PR

[Claude Paroz <claude@…>]

In a08d2463:

Fixed #26112 -- Error when computing aggregate of GIS areas.

Thanks Simon Charette and Claude Paroz for the reviews.

[Tim Graham]

The new test fails on Oracle:

  File "/home/tim/code/django/tests/gis_tests/geoapp/test_functions.py", line 243, in test_area_with_regular_aggregate
    for c in qs:
...
ORA-22901: cannot compare VARRAY or LOB attributes of an object type

[Shai Berger]

Oracle-fixing ​PR

[Shai Berger]

When I submitted the PR I was doubtful about it being the right solution, but now I've convinced myself that it is.

[Tim Graham <timograham@…>]

In bb51dc9:

Refs #26112 -- Fixed aggregate GIS test on Oracle.

Made sure the test doesn't try to aggregate over MultiPolygonField and made
AreaField turn decimals into floats on the way from the DB.

Thanks Daniel Wiesmann, Jani Tiainen, and Tim Graham for review and discussion.