如何使用south管理的现有应用程序设置Django hstore？

Question

我试图使用django hstore使用this nice tutorial。我在South管理的现有应用程序中添加了两个类：

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()

生成一个schemamigration --auto，启动迁移并获得一个django.db.utils.DatabaseError: type "hstore" does not exist。

好吧，图图似乎不完整，django hstoredocumentation告诉我使用自定义数据库后端，我在设置文件中添加了以下内容：

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

然后我在south/db/__init__.py", line 78中得到一个KeyError: 'default'。此时，intertubes+一些试用/错误将我指向SOUTH_DATABASE_ADAPTERS设置变量，并将以下内容添加到设置中：

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

新错误：

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

现在这很奇怪，因为我安装了hstore扩展：

$ 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)

怎么会这样？我用的是Django 1.4，Postgresql 9.1。

Answer 1

自从我的最后一个答案以来，Django已经弃用并删除了pre_syncdb信号。我已经更新了答案以适应更新的版本。新版本的基本机制是相同的，因为这两个方法都依赖于信号和仅在HSTORE扩展不存在时执行的SQL代码。

姜戈1.8+

自从Django引入DB迁移以来，pre_syncdb信号是marked deprecated in 1.7和completely removed in 1.9。然而，他们引入了一个名为^{}的新信号，可以用同样的方式使用。

示例：

"""
This is an example models.py which contains all model definition.
"""
from django.db import connection, models
from django.db.models.signals import pre_migrate
from django.dispatch import receiver
import sys

# sender is optional but will be called for every pre_migrate signal if removed
@receiver(pre_migrate, sender=sys.modules[__name__])
def setup_postgres_hstore(sender, **kwargs):
    """
    Always create PostgreSQL HSTORE extension if it doesn't already exist
    on the database before syncing the database.
    Requires PostgreSQL 9.1 or newer.
    """
    cursor = connection.cursor()
    cursor.execute("CREATE EXTENSION IF NOT EXISTS hstore")

# ...rest of your model definition goes here
class Foo(models.Model):
    # ...field definitions, etc.

---

Django 1.6+（原始答案）

确保HSTORE扩展在./manage.py syncdb期间安装的一种方法是利用pre_syncdb文件中的models.py信号，该文件是用Django 1.6引入的。

示例：

"""
This is an example models.py which contains all model definition.
"""
from django.db import connection, models
from django.db.models.signals import pre_syncdb
from django.dispatch import receiver
import sys

# sender is optional but will be called for every pre_syncdb signal if removed
@receiver(pre_syncdb, sender=sys.modules[__name__])
def setup_postgres_hstore(sender, **kwargs):
    """
    Always create PostgreSQL HSTORE extension if it doesn't already exist
    on the database before syncing the database.
    Requires PostgreSQL 9.1 or newer.
    """
    cursor = connection.cursor()
    cursor.execute("CREATE EXTENSION IF NOT EXISTS hstore")

# ...rest of your model definition goes here
class Foo(models.Model):
    # ...field definitions, etc.

我发现如果你不想为每个新的数据库实例运行它，这是很有用的。此方法也适用于测试数据库设置期间的Django单元测试。

关于Django中信号钩子的更多信息： https://docs.djangoproject.com/en/1.6/ref/signals/#management-signals

Answer 2

Django现在包括a migration operation to create the ^{} extension in PostgreSQL：

from django.contrib.postgres.operations import HStoreExtension

class Migration(migrations.Migration):
    ...

    operations = [
        HStoreExtension(),
        ...
    ]

Answer 3

我最终发现没有为我使用的特定数据库安装hstore扩展：

$ 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)

我以为在hstore安装之后创建的数据库会包含扩展。似乎不是这样，am I misinterpreting how extensions work ? Are they database-specific ?