Pluggable Django Application Patterns PyCon 2011

Pluggable PatternsFor Reusable Django Applications

Friday, March 11, 2011

An app should not be a monolithic pile of code

For example, most blog “apps” available provide too much functionality

MyBlog App• Categories• Custom Tagging• Custom Comments • Comment

Moderation• Assumption of text

markup type• Single blogs• Multiple Sites

ACME MONOLITHS


An application should be “pluggable”


FocusedWrite programs that do one thing and do it well.

— Doug McIlroy (inventor of UNIX pipes)

A “pluggable” app is


http://en.wikipedia.org/wiki/Computer_program

http://en.wikipedia.org/wiki/Computer_program

Self-ContainedBatteries are included

Dependencies are declared

A “pluggable” app is


Easily AdaptableA “pluggable” app is

Corey’s Law: The less adaptable you make your code, the sooner you will be tasked to adapt it.


Easily InstalledA “pluggable” app is

pip install coolappYou did declare your dependencies, right?


How do we make a “pluggable” application?


Stop thinking like this

http://upload.wikimedia.org/wikipedia/commons/archive/a/aa/20090315161532!Ferrari_Enzo_Ferrari.JPGFriday, March 11, 2011

and think like this


Applications can have very different purposes

http://www.flickr.com/photos/tiemposdelruido/4051083769/Friday, March 11, 2011

Application Types

• Data. Manages specific data and access to itdjango.contrib.auth

• Utility. Provide a way of handling a specific problem for any applicationdjango-pagination, django.contrib.webdesign

• Decorator. Adds functionality to one or aggregates functionality of many applicationsdjango-mptt, django-tagging


Situation 1

You want to configure your app without modifying its code

(e.g. API keys)


Configurable Options

from django.conf import settings

MODULES = getattr(settings, 'SUPERTAGGING_MODULES', {})

Django Supertagging http://github.com/josesoa

Internal Name Setting Name Default Value


Configurable Options

from django.conf import settings

TOOLBAR_CONFIG = { 'INTERCEPT_REDIRECTS': True, 'SHOW_TOOLBAR_CALLBACK': default_show_toolbar, 'EXTRA_SIGNALS': [], 'HIDE_DJANGO_SQL': True, 'SHOW_TEMPLATE_CONTEXT': True, 'TAG': 'body',}

TOOLBAR_CONFIG.update(getattr(settings, 'DEBUG_TOOLBAR_CONFIG', {}))

Django Debug Toolbar http://github.com/robhudson


Data Apps

http://www.flickr.com/photos/29276244@N03/3200630853/Friday, March 11, 2011

Situation 2

Lots of variationsEach implementation is different

(e.g. blogs)


Abstract Models

EntryBase

FeaturableEntryMixin

StatusableEntryMixin

TaggableEntryMixin

HTMLFormattableEntryMixin

GLAMKit http://www.glamkit.org/

class PRBlog(EntryBase, StatusableEntryMixin):

subhead = models.CharField(… pdf = models.FileField(…


Situation 3

A few, well-known of variations(e.g. Use django.contrib.sites?)


Optional Field Settings

from django.db import modelsfrom myapp.settings import MULTIPLE_SITES

if MULTIPLE_SITES: from django.contrib.sites.models import Site

class Entry(models.Model): title = models.CharField(max_length=100) … if MULTIPLE_SITES: sites = models.ManyToManyField(Site)


Situation 4

Optionally use another application

(e.g. Use django-tagging?)


Optional Integration

from django.db import modelsfrom myapp.settings import USE_TAGGING

if USE_TAGGING: from tagging.fields import TagField

class Entry(models.Model): title = models.CharField(max_length=100) … if USE_TAGGING: tags = TagField()


Situation 5

You want to reference different models

(e.g. Customizable author field)


Runtime Configurable Foreign Keys

from django.conf import settingsfrom django.db.models import get_model

model_string = getattr(settings, 'VIEWPOINT_AUTHOR_MODEL', 'auth.User')AUTHOR_MODEL = get_model(*model_string.split('.'))

Viewpoint http://github.com/washingtontimes


Runtime Configurable Foreign Keys

from viewpoint.settings import AUTHOR_MODEL

class Entry(models.Model): title = models.CharField(max_length=100) author = models.ForeignKey(AUTHOR_MODEL) …

Viewpoint http://github.com/washingtontimes


Utility Apps

http://www.flickr.com/photos/s8/3638531205/Friday, March 11, 2011

Required for template tags or

management commands

models.py


Decorator Apps

http://www.flickr.com/photos/yum9me/2109549869/Friday, March 11, 2011

New FieldNew Method

New AdminCustom Manager


Situation 6

You want to add a field to a model


Lazy Field InsertionDjango Categories http://github.com/washingtontimes


Lazy Field Insertion

CATEGORY_FOREIGNKEYS = { 'app1.Model': ('category',) 'app2.Model': ('primary_category', 'secondary_category')}

Django Categories http://github.com/washingtontimes


Lazy Field Insertionfrom django.db.models import get_modelimport django.conf import settings

FOREIGNKEYS = getattr(settings, 'CATEGORY_FOREIGNKEYS', {})

for model_name, cat_fields in FOREIGNKEYS.items(): if not isinstance(model_name, basestring): continue model = get_model(*model_name.split('.')) for category_field in list(cat_fields): try: model._meta.get_field(category_field) except FieldDoesNotExist: ForeignKey(Category).contribute_to_class( model, category_field)

Django Categories http://github.com/washingtontimes


Situation 7

You want to add a custom manager to a model


Lazy Manager Insertion

COOLAPP_MODELS = { 'app1.Model': 'cool_manager', 'app2.Model': 'cool_manager',}

Django MPTT http://github.com/django-mptt


Adding a manager

from django.db.models import get_modelimport django.conf import settingsfrom coolapp.managers import CustomManager

MODELS = getattr(settings, 'COOLAPP_MODELS', {})

for model_name, mgr_name in MODELS.items(): if not isinstance(model_name, basestring): continue model = get_model(*model_name.split('.')) if not getattr(model, mgr_name, False): manager = CustomManager() manager.contribute_to_class(model, mgr_name)

Django MPTT http://github.com/django-mptt


Situation 8

You want to customize a model’s ModelAdmin

(e.g. Change the widget of a field)


Lazy Registration of a Custom ModelAdmin

TINYMCE_ADMIN_FIELDS = { 'app1.model1': ('body',), 'app1.model2': ('blog_text', 'blog_teaser')}

Django TinyMCE http://github.com/justquick

project’s settings.pyFriday, March 11, 2011


from django.db.models import get_modelimport django.conf import settings

REGISTRY = {}ADMIN_FIELDS = getattr(settings, 'TINYMCE_ADMIN_FIELDS', {})

for model_name, field in ADMIN_FIELDS.items(): if isinstance(model_name, basestring): model = get_model(*model_name.split('.')) if model in registry: return REGISTRY[model] = field


Django-TinyMCE’s models.pyFriday, March 11, 2011


# Define a new ModelAdmin subclass

class TinyMCEAdmin(admin.ModelAdmin): editor_fields = ()

def formfield_for_dbfield(self, db_field, **kwargs): if db_field.name in self.editor_fields: return db_field.formfield(widget=TinyMCE()) return super(TinyMCEAdmin, self).formfield_for_dbfield( db_field, **kwargs)


Django-TinyMCE’s admin.pyFriday, March 11, 2011


for model, modeladmin in admin.site._registry.items(): if model in REGISTRY: admin.site.unregister(model) admin.site.register( model, type('newadmin', (TinyMCEAdmin, modeladmin.__class__), {'editor_fields': REGISTRY[model],} ) )


bottom of Django-TinyMCE’s admin.pyFriday, March 11, 2011

Touch Points


Touch Points of an App

The parts of an application that usually need tweaking• URLs• Templates• View responses


Situation 9

You want the URLs of your app to live under any prefix

(e.g. /blogs/ vs. /weblogs/)


Name your URLs

from django.conf.urls.defaults import *

urlpatterns = patterns('', (r'^$', 'coolapp_app.views.index'),)


Name your URLs

from django.conf.urls.defaults import *

urlpatterns = patterns('', url(r'^$', 'coolapp_app.views.index', name='coolapp_index'),)

url Function name


Reference your URLs by name

<p>Go to the <a href="{% url coolapp_index %}">Index</a></p>

from django.core.urlresolvers import reverse

def myview(request): return HttpResponseRedirect(reverse('coolapp_index', args=[]))


Situation 10

You want your templates to be easily overridable


“Namespace” Templates

coolapp

templates

coolapp

All templates in a template

“name space”

base.html


“Namespace” Templates

coolapp

templates

coolapp

Referenced as “coolapp/base.html”

base.html


Extend one template

index.html

base.html

detail.htmlsummary.html

{% extends “base.html” %}

site_base.html


Extend one template

index.html

base.html


{% extends “coolapp/base.html” %}base.html

site_base.html


Extend one template

index.html

base.html


{% extends “coolapp/base.html” %}base.html

site_base.html


Extend one template

coolapp/base.html

{% extends "base.html" %}

{% block head %}{% endblock %}

{% block body %}{% endblock %}


Extend one template

coolapp/base.html

{% extends "base.html" %}

{% block head %}{% endblock %}

{% block body %}{% endblock %}

{% extends "site_base.html" %}

{% block extra_head %} {% block head %} {% endblock %}{% endblock %}

{% block content %} {% block body %} {% endblock %}{% endblock %}


Import your blocks

{% extends "coolapp/base.html" %}

{% block extra_head %} {{ block.super }} {% import "coolapp/extra_head.html" %}{% endblock %}

{% block content %} {# Important content stuff here #}

{% endblock %}

extra_head.html

coolapp/detail.html

Allows you to override any of the templates


Situation 11

You want flexibility storing uploaded files


Define a Storage Optionfrom django.conf import settingsfrom django.core.files.storage import get_storage_class

DEFAULT_STORAGE = get_storage_class(getattr(settings, "MMEDIA_DEFAULT_STORAGE", settings.DEFAULT_FILE_STORAGE)

)

from massmedia.settings import IMAGE_UPLOAD_TO, DEFAULT_STORAGE

class Image(models.Model): file = models.FileField( upload_to = IMAGE_UPLOAD_TO, blank = True, null = True, storage=DEFAULT_STORAGE())


Situation 12

You want to alter the data your views use

(e.g. Extra context, different template)


100% more class-based views!

django-cbv for backwards

compatibility!


My Info

• [email protected]

• @coordt

• github.com/coordt

• github.com/washingtontimes

• opensource.washingtontimes.com


Technology

Pluggable Django Application Patterns PyCon 2011