id	summary	reporter	owner	description	type	status	component	version	severity	resolution	keywords	cc	stage	has_patch	needs_docs	needs_tests	needs_better_patch	easy	ui_ux
21346	GeoDjango query repeatedly executed in loop	django@…	nobody	"I'm running Django 1.5.5 on OSX 10.7.5 with Python 2.7.5 and PostgreSQL 9.3.1 and PostGIS version 2.1.0""

{{{
""POSTGIS=""2.1.0 r11822"" GEOS=""3.4.2-CAPI-1.8.2 r3921"" PROJ=""Rel. 4.8.0, 6 March 2012"" GDAL=""GDAL 1.10.1, released 2013/08/26"" LIBXML=""2.9.1"" LIBJSON=""UNKNOWN"" TOPOLOGY RASTER""
}}}

I've discovered what appears to be a bug causing GeoDjango queries to be repeatedly executed. What I'm doing here is seeing what locations touch other locations. In this specific example, I'm querying France. My database is populated from the [http://www.naturalearthdata.com/downloads/10m-cultural-vectors/10m-admin-0-countries/ Natural Earth dataset].

{{{#!python
print datetime.datetime.now()
touching_locations = Location.objects.filter(geometry__touches=Location.objects.get(name='France').geometry).values_list('name', flat=True)
print type(touching_locations)
for i in range(10):
    print datetime.datetime.now(), touching_locations
print datetime.datetime.now()
}}}

Output:

{{{
2013-10-28 16:09:14.958192
<class 'django.contrib.gis.db.models.query.GeoValuesListQuerySet'>
2013-10-28 16:09:14.974053 [u'Belgium', u'Brazil', u'Germany', u'Spain', u'Italy']
2013-10-28 16:09:22.576670 [u'Belgium', u'Brazil', u'Germany', u'Spain', u'Italy']
2013-10-28 16:09:30.089413 [u'Belgium', u'Brazil', u'Germany', u'Spain', u'Italy']
2013-10-28 16:09:37.616438 [u'Belgium', u'Brazil', u'Germany', u'Spain', u'Italy']
2013-10-28 16:09:45.119495 [u'Belgium', u'Brazil', u'Germany', u'Spain', u'Italy']
2013-10-28 16:09:52.664080 [u'Belgium', u'Brazil', u'Germany', u'Spain', u'Italy']
2013-10-28 16:10:00.197783 [u'Belgium', u'Brazil', u'Germany', u'Spain', u'Italy']
2013-10-28 16:10:07.730839 [u'Belgium', u'Brazil', u'Germany', u'Spain', u'Italy']
2013-10-28 16:10:15.270071 [u'Belgium', u'Brazil', u'Germany', u'Spain', u'Italy']
2013-10-28 16:10:22.898417 [u'Belgium', u'Brazil', u'Germany', u'Spain', u'Italy']
2013-10-28 16:10:30.429394
}}}

So, you can see that there's about 8 seconds between print statements. This is obviously because it's repeatedly executing the query. Now, if I force the query to be stored in a list, I see the performance I expect:

{{{#!python
print datetime.datetime.now()
touching_locations = [x for x in Location.objects.filter(geometry__touches=Location.objects.get(name='France').geometry).values_list('name', flat=True)]
print type(touching_locations)
for i in range(10):
    print datetime.datetime.now(), touching_locations
print datetime.datetime.now()
}}}

{{{
2013-10-28 16:11:58.997853
<type 'list'>
2013-10-28 16:12:06.539672 [u'Belgium', u'Brazil', u'Germany', u'Spain', u'Italy']
2013-10-28 16:12:06.539702 [u'Belgium', u'Brazil', u'Germany', u'Spain', u'Italy']
2013-10-28 16:12:06.539714 [u'Belgium', u'Brazil', u'Germany', u'Spain', u'Italy']
2013-10-28 16:12:06.539724 [u'Belgium', u'Brazil', u'Germany', u'Spain', u'Italy']
2013-10-28 16:12:06.539734 [u'Belgium', u'Brazil', u'Germany', u'Spain', u'Italy']
2013-10-28 16:12:06.539744 [u'Belgium', u'Brazil', u'Germany', u'Spain', u'Italy']
2013-10-28 16:12:06.539755 [u'Belgium', u'Brazil', u'Germany', u'Spain', u'Italy']
2013-10-28 16:12:06.539765 [u'Belgium', u'Brazil', u'Germany', u'Spain', u'Italy']
2013-10-28 16:12:06.539775 [u'Belgium', u'Brazil', u'Germany', u'Spain', u'Italy']
2013-10-28 16:12:06.539784 [u'Belgium', u'Brazil', u'Germany', u'Spain', u'Italy']
2013-10-28 16:12:06.539804
}}}

Now, you can see that the query is just called once, and performance is much better."	Bug	closed	GIS	1.5	Normal	invalid			Unreviewed	0	0	0	0	0	0