Maxime R. Maxime R. - 2 months ago 22
Python Question

How to setup django-hstore with an existing app managed by south?

I tried to use django-hstore using this nice tutorial. I added two classes to an existing app managed by South:



class Attribute(models.Model):
name = models.CharField(max_length=200, verbose_name=_("name"))
description = models.CharField(max_length=1000, verbose_name=_("description"))

class Measure(models.Model):
attribute = models.ForeignKey(Attribute)
data = hstore.DictionaryField(db_index=True)
objects = hstore.HStoreManager()


made a
schemamigration --auto
, launched the migration and got a
django.db.utils.DatabaseError: type "hstore" does not exist
.

Okay, the tuto seemed to be incomplete, the django-hstore documentation told me to use the custom database backend, i added the following to my settings file:



DATABASES['default']['ENGINE'] = 'django_hstore.postgresql_psycopg2'


Then I got a
KeyError: 'default'
in
south/db/__init__.py", line 78
. At this point, the intertubes + some trial/errors pointed me to the
SOUTH_DATABASE_ADAPTERS
settings variable and I added the following to the settings:



SOUTH_DATABASE_ADAPTERS = {'default': 'south.db.postgresql_psycopg2'}


New error:

File ".../psycopg2/extras.py", line 769, in register_hstore
"hstore type not found in the database. "
psycopg2.ProgrammingError: hstore type not found in the database. please install it from your 'contrib/hstore.sql' file


Now this is odd because I installed the hstore extension :



$ sudo -u postgres psql
create extension hstore;
postgres=# CREATE EXTENSION hstore;
ERROR: extension "hstore" already exists
postgres=# \dx
List of installed extensions
Name | Version | Schema | Description
---------+---------+------------+--------------------------------------------------
hstore | 1.0 | public | data type for storing sets of (key, value) pairs
plpgsql | 1.0 | pg_catalog | PL/pgSQL procedural language
(2 rows)
postgres=# SELECT 'hstore'::regtype::oid;
oid
-------
57704
(1 row)


How is this supposed to work ? I'm using Django 1.4, Postgresql 9.1.

Answer

I eventually found that the hstore extension wasn't installed for the specific database I was using:

$ psql -d mydb
psql (9.1.4)
Type "help" for help.

mydb=# SELECT t.oid, typarray FROM pg_type t JOIN pg_namespace ns ON typnamespace = ns.oid WHERE typname = 'hstore';
 oid | typarray 
-----+----------
(0 rows)

mydb=# \dx
                 List of installed extensions
  Name   | Version |   Schema   |         Description          
---------+---------+------------+------------------------------
 plpgsql | 1.0     | pg_catalog | PL/pgSQL procedural language
(1 row)

mydb=# create extension hstore;
WARNING:  => is deprecated as an operator name
DETAIL:  This name may be disallowed altogether in future versions of PostgreSQL.
CREATE EXTENSION
mydb=# \dx
                           List of installed extensions
  Name   | Version |   Schema   |                   Description                    
---------+---------+------------+--------------------------------------------------
 hstore  | 1.0     | public     | data type for storing sets of (key, value) pairs
 plpgsql | 1.0     | pg_catalog | PL/pgSQL procedural language
(2 rows)

mydb=# SELECT t.oid, typarray FROM pg_type t JOIN pg_namespace ns ON typnamespace = ns.oid WHERE typname = 'hstore';
  oid  | typarray 
-------+----------
 58800 |    58805
(1 row)

I thought that a database created after the hstore installation would include the extension. Doesn't seem to be the case, am I misinterpreting how extensions work ? Are they database-specific ?