Django Solo

+---------------------------+
|                           |
|                           |
|             \             | Django Solo helps working with singletons:
|             /\            | database tables that only have one row.
|           >=)'>           | Singletons are useful for things like global
|             \/            | settings that you want to edit from the admin
|             /             | instead of having them in Django settings.py.
|                           | 
|                           | 
+---------------------------+

Features

Solo helps you enforce instantiating only one instance of a model in django.

• You define the model that will hold your singleton object.
• django-solo gives helper parent class for your model and the admin classes.
• You get an admin interface that's aware you only have one object.
• You can retrieve the object from templates.
• By enabling caching, the database is not queried intensively.

Use Cases

Django Solo is also great for use with singleton objects that have a one to many relationship. Like the use case below where you have a 'Home Slider" that has many "Slides".

• Global or default settings
• An image slider that has many slides
• A page section that has sub-sections
• A team bio with many team members

There are many cases where it makes sense for the parent in a one to many relationship to be limited to a single instance.

Usage Example

# models.py

from django.db import models
from solo.models import SingletonModel

class SiteConfiguration(SingletonModel):
    site_name = models.CharField(max_length=255, default='Site Name')
    maintenance_mode = models.BooleanField(default=False)

    def __unicode__(self):
        return u"Site Configuration"

    class Meta:
        verbose_name = "Site Configuration"

# admin.py

from django.contrib import admin
from solo.admin import SingletonModelAdmin
from config.models import SiteConfiguration

admin.site.register(SiteConfiguration, SingletonModelAdmin)

# There is only one item in the table, you can get it this way:
from .models import SiteConfiguration
config = SiteConfiguration.objects.get()

# get_solo will create the item if it does not already exist
config = SiteConfiguration.get_solo()

In your model, note how you did not have to provide a verbose_name_plural field - That's because Django Solo uses the verbose_name instead.

If you're changing an existing model (which already has some objects stored in the database) to a singleton model, you can explicitly provide the id of the row in the database for django-solo to use. This can be done by setting singleton_instance_id property on the model:

class SiteConfiguration(SingletonModel):
    singleton_instance_id = 24
    # (...)

Installation

This application requires Django >= 1.6.

• Install the package using pip install django-solo
• Add solo or solo.apps.SoloAppConfig to your INSTALLED_APPS setting.

This is how you run tests:

./manage.py test solo --settings=solo.tests.settings

Admin

The standard Django admin does not fit well when working with singleton, for instance, if you need some global site settings to be edited in the admin. Django Solo provides a modified admin for that.

• In the admin home page where all applications are listed, we have a config application that holds a singleton model for site configuration.
• The configuration object can only be changed, there's no link for "add" (1).
• The link to the configuration page (2) directly goes to the form page - no need for an intermediary object list page, since there's only one object.
• The edit page has a modified breadcrumb (3) to avoid linking to the intermediary object list page.
• From the edit page, we cannot delete the object (4) nor can we add a new one (5).

Availability from templates

The singleton object can be retrieved from template by giving the Django model dotted path:

{% get_solo 'app_label.ModelName' as my_config %}

Example:

{% load solo_tags %}
{% get_solo 'config.SiteConfiguration' as site_config %}
{{ site_config.site_name }}
{{ site_config.maintenance_mode }}

If you're extending a template, be sure to use the tag in the proper scope.

Right:

{% extends "index.html" %}
{% load solo_tags %}

{% block content %}
    {% get_solo 'config.SiteConfiguration' as site_config %}
    {{ site_config.site_name }}
{% endblock content %}

Wrong:

{% extends "index.html" %}
{% load solo_tags %}
{% get_solo 'config.SiteConfiguration' as site_config %}

{% block content %}
    {{ site_config.site_name }}
{% endblock content %}

Caching

By default caching is disabled: every time get_solo retrieves the singleton object, there will be a database query.

You can enable caching to only query the database when initially retrieving the object. The cache will also be updated when updates are made from the admin.

The cache timeout is controlled via the SOLO_CACHE_TIMEOUT settings. The cache backend to be used is controlled via the SOLO_CACHE settings.

Settings

Template Tag Name

You can retrieve your singleton object in templates using the get_solo template tag.

You can change the name get_solo using the GET_SOLO_TEMPLATE_TAG_NAME setting.

GET_SOLO_TEMPLATE_TAG_NAME = 'get_config'

Cache backend

Django provides a way to define multiple cache backends with the CACHES settings. If you want the singleton object to be cached separately, you could define the CACHES and the SOLO_CACHE settings like this:

CACHES = {
    'default': {
        'BACKEND': 'django.core.cache.backends.memcached.MemcachedCache',
        'LOCATION': '127.0.0.1:11211',
    },
    'local': {
        'BACKEND': 'django.core.cache.backends.locmem.LocMemCache',
    },
}

SOLO_CACHE = 'local'

Caching will be disabled if set to None.

Cache timeout

The cache timeout in seconds.

SOLO_CACHE_TIMEOUT = 60*5  # 5 mins

Cache prefix

The prefix to use for the cache key.

SOLO_CACHE_PREFIX = 'solo'

Getting the code

The code is hosted at https://github.com/lazybird/django-solo/

Check out the latest development version anonymously with::

$ git clone git://github.com/lazybird/django-solo.git