PosGis and Django-Tenants - django

Question

(Using the library django-tenants for tenant separated multi-tenancy) For PostGis support the docs say to add ORIGINAL_BACKEND = "django.contrib.gis.db.backends.postgis". I have this, however, when I go to create a new tenant I get the following error:
Traceback (most recent call last):
File "c:\users\cole\appdata\local\programs\python\python36-32\lib\site-packages\celery\app\trace.py", line 382, in trace_task
R = retval = fun(*args, **kwargs)
File "c:\users\cole\appdata\local\programs\python\python36-32\lib\site-packages\celery\app\trace.py", line 641, in __protected_call__
return self.run(*args, **kwargs)
File "C:\Users\Cole\Documents\GitHub\Elevate-RA-Django-App\returns_app\apps\tenant_stores\tasks.py", line 28, in create_tenant_task
tenant.save()
File "c:\users\cole\appdata\local\programs\python\python36-32\lib\site-packages\django_tenants\models.py", line 93, in save
self.create_schema(check_if_exists=True, verbosity=verbosity)
File "c:\users\cole\appdata\local\programs\python\python36-32\lib\site-packages\django_tenants\models.py", line 143, in create_schema
verbosity=verbosity)
File "c:\users\cole\appdata\local\programs\python\python36-32\lib\site-packages\django\core\management\__init__.py", line 141, in call_command
return command.execute(*args, **defaults)
File "c:\users\cole\appdata\local\programs\python\python36-32\lib\site-packages\django\core\management\base.py", line 335, in execute
output = self.handle(*args, **options)
File "c:\users\cole\appdata\local\programs\python\python36-32\lib\site-packages\django_tenants\management\commands\migrate_schemas.py", line 63, in handle
executor.run_migrations(tenants=tenants)
File "c:\users\cole\appdata\local\programs\python\python36-32\lib\site-packages\django_tenants\migration_executors\standard.py", line 15, in run_migrations
run_migrations(self.args, self.options, self.codename, schema_name, idx=idx, count=len(tenants))
File "c:\users\cole\appdata\local\programs\python\python36-32\lib\site-packages\django_tenants\migration_executors\base.py", line 34, in run_migrations
MigrateCommand(stdout=stdout, stderr=stderr).execute(*args, **options)
File "c:\users\cole\appdata\local\programs\python\python36-32\lib\site-packages\django\core\management\base.py", line 335, in execute
output = self.handle(*args, **options)
File "c:\users\cole\appdata\local\programs\python\python36-32\lib\site-packages\django\core\management\commands\migrate.py", line 77, in handle
connection.prepare_database()
File "c:\users\cole\appdata\local\programs\python\python36-32\lib\site-packages\django\contrib\gis\db\backends\postgis\base.py", line 26, in prepare_database
cursor.execute("CREATE EXTENSION IF NOT EXISTS postgis")
File "c:\users\cole\appdata\local\programs\python\python36-32\lib\site-packages\django\db\backends\utils.py", line 100, in execute
return super().execute(sql, params)
File "c:\users\cole\appdata\local\programs\python\python36-32\lib\site-packages\django\db\backends\utils.py", line 68, in execute
return self._execute_with_wrappers(sql, params, many=False, executor=self._execute)
File "c:\users\cole\appdata\local\programs\python\python36-32\lib\site-packages\django\db\backends\utils.py", line 77, in _execute_with_wrappers
return executor(sql, params, many, context)
File "c:\users\cole\appdata\local\programs\python\python36-32\lib\site-packages\django\db\backends\utils.py", line 85, in _execute
return self.cursor.execute(sql, params)
File "c:\users\cole\appdata\local\programs\python\python36-32\lib\site-packages\django\db\utils.py", line 89, in __exit__
raise dj_exc_value.with_traceback(traceback) from exc_value
File "c:\users\cole\appdata\local\programs\python\python36-32\lib\site-packages\django\db\backends\utils.py", line 83, in _execute
return self.cursor.execute(sql)
django.db.utils.ProgrammingError: relation "spatial_ref_sys" does not exist
The spatial_ref_sys table exists within my public schema. The django.contrib.gis app is in my shared apps.
Any ideas?

Answer 1

The issue seems to be cause by the default PostGis backend, specifically the call to prepare the database for migration, by explicitly setting the search path prior to calling CREATE EXTENSION IF NOT EXISTS postgis I was able to migrate/create a schema by creating a custom DB backend that overrides this behaviour:
from django.contrib.gis.db.backends.postgis.base import (
DatabaseWrapper as OriginalPostGisDatabaseWrapper,
)
from django_tenants.utils import get_public_schema_name
class DatabaseWrapper(OriginalPostGisDatabaseWrapper):
"""
This database wrapper explicitly sets the search path when preparing the database, as
multi-schema environments (like with Django-tenants) can cause issues with the PostGis
backend.
"""
def __init__(self, *args, **kwargs):
super().__init__(*args, **kwargs)
self.PUBLIC_SCHEMA_NAME = get_public_schema_name()
def prepare_database(self):
# Check that postgis extension is installed.
with self.cursor() as cursor:
cursor.execute('SET search_path = %s', params=[self.PUBLIC_SCHEMA_NAME])
cursor.execute("CREATE EXTENSION IF NOT EXISTS postgis")
Then, set your ORIGINAL_BACKEND setting to the location of the above DB backend instead of the standard PostGis backend.