#25446: Can't use PostGIS function ST_OrderingEquals with GeoDjango
-----------------------------+--------------------------------------
Reporter: ezheidtmann | Owner: nobody
Type: Bug | Status: new
Component: GIS | Version: 1.8
Severity: Normal | Resolution:
Keywords: | Triage Stage: Unreviewed
Has patch: 0 | Needs documentation: 0
Needs tests: 0 | Patch needs improvement: 0
Easy pickings: 0 | UI/UX: 0
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Changes (by ezheidtmann):
* needs_better_patch: => 0
* needs_tests: => 0
* needs_docs: => 0
Old description:
> Unless I'm missing something, Django 1.8 provides no facility in the ORM
> to use the ST_OrderingEquals() function to compare two geometries. I
> would like to use this function in a query.
>
> Am I correct? If so, I may attempt a patch or at least a workaround.
>
> Thanks!
>
> Ref: http://postgis.net/docs/manual-1.3/ch06.html#ST_OrderingEquals
New description:
Unless I'm missing something, Django 1.8 provides no facility in the ORM
to use the ST_OrderingEquals() function to compare two geometries. I would
like to use this function in a query.
Am I correct? If so, I may attempt a patch or at least a workaround.
Thanks!
Ref: http://postgis.net/docs/manual-1.3/ch06.html#ST_OrderingEquals
P.S. It's another question entirely whether the '__exact' lookup should
use this function. For comparison, two LineString objects with opposite
vertex ordering are not considered equal, so why should they be considered
equal at the DB level?
--
Comment:
For other users who may find this, here's my workaround that allows me to
find the geometry that matches an input geometry, both in vertex values
and in vertex ordering. A Django wizard may be able to improve this and I
would welcome any criticism.
{{{
class SegmentModel(models.Model):
...
@classmethod
def get_or_create_for_line(cls, line):
from django.contrib.gis.db.backends.postgis.adapter import
PostGISAdapter
sql = 'SELECT * FROM ride_segment WHERE line ~= {line_serialized}
AND ST_OrderingEquals(line, {line_serialized})'.format(
line_serialized=str(PostGISAdapter(line)))
segments = list(cls.objects.raw(sql))
if len(segments) > 1:
from django.db import IntegrityError
raise IntegrityError('Multiple segments for line
{}'.format(line.ewkt))
elif len(segments) == 0:
return (True, cls.objects.create(line=line))
else:
return (False, segments[0])
}}}
--
Ticket URL: <https://code.djangoproject.com/ticket/25446#comment:1>
Django <https://code.djangoproject.com/>
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