Because Django was developed in a fast-paced newsroom environment, it was\ndesigned to make common Web-development tasks fast and easy. Here’s an informal\noverview of how to write a database-driven Web app with Django.
\nThe goal of this document is to give you enough technical specifics to\nunderstand how Django works, but this isn’t intended to be a tutorial or\nreference – but we’ve got both! When you’re ready to start a project, you can\nstart with the tutorial or dive right into more\ndetailed documentation.
\nAlthough you can use Django without a database, it comes with an\nobject-relational mapper in which you describe your database layout in Python\ncode.
\nThe data-model syntax offers many rich ways of\nrepresenting your models – so far, it’s been solving many years’ worth of\ndatabase-schema problems. Here’s a quick example:
\nmysite/news/models.pyfrom django.db import models\n\nclass Reporter(models.Model):\n full_name = models.CharField(max_length=70)\n\n def __str__(self): # __unicode__ on Python 2\n return self.full_name\n\nclass Article(models.Model):\n pub_date = models.DateField()\n headline = models.CharField(max_length=200)\n content = models.TextField()\n reporter = models.ForeignKey(Reporter, on_delete=models.CASCADE)\n\n def __str__(self): # __unicode__ on Python 2\n return self.headline\nNext, run the Django command-line utility to create the database tables\nautomatically:
\n$ python manage.py migrate\nThe migrate command looks at all your available models and creates\ntables in your database for whichever tables don’t already exist, as well as\noptionally providing much richer schema control.
With that, you’ve got a free, and rich, Python API\nto access your data. The API is created on the fly, no code generation\nnecessary:
\n# Import the models we created from our "news" app\n>>> from news.models import Reporter, Article\n\n# No reporters are in the system yet.\n>>> Reporter.objects.all()\n<QuerySet []>\n\n# Create a new Reporter.\n>>> r = Reporter(full_name='John Smith')\n\n# Save the object into the database. You have to call save() explicitly.\n>>> r.save()\n\n# Now it has an ID.\n>>> r.id\n1\n\n# Now the new reporter is in the database.\n>>> Reporter.objects.all()\n<QuerySet [<Reporter: John Smith>]>\n\n# Fields are represented as attributes on the Python object.\n>>> r.full_name\n'John Smith'\n\n# Django provides a rich database lookup API.\n>>> Reporter.objects.get(id=1)\n<Reporter: John Smith>\n>>> Reporter.objects.get(full_name__startswith='John')\n<Reporter: John Smith>\n>>> Reporter.objects.get(full_name__contains='mith')\n<Reporter: John Smith>\n>>> Reporter.objects.get(id=2)\nTraceback (most recent call last):\n ...\nDoesNotExist: Reporter matching query does not exist.\n\n# Create an article.\n>>> from datetime import date\n>>> a = Article(pub_date=date.today(), headline='Django is cool',\n... content='Yeah.', reporter=r)\n>>> a.save()\n\n# Now the article is in the database.\n>>> Article.objects.all()\n<QuerySet [<Article: Django is cool>]>\n\n# Article objects get API access to related Reporter objects.\n>>> r = a.reporter\n>>> r.full_name\n'John Smith'\n\n# And vice versa: Reporter objects get API access to Article objects.\n>>> r.article_set.all()\n<QuerySet [<Article: Django is cool>]>\n\n# The API follows relationships as far as you need, performing efficient\n# JOINs for you behind the scenes.\n# This finds all articles by a reporter whose name starts with "John".\n>>> Article.objects.filter(reporter__full_name__startswith='John')\n<QuerySet [<Article: Django is cool>]>\n\n# Change an object by altering its attributes and calling save().\n>>> r.full_name = 'Billy Goat'\n>>> r.save()\n\n# Delete an object with delete().\n>>> r.delete()\nOnce your models are defined, Django can automatically create a professional,\nproduction ready administrative interface –\na website that lets authenticated users add, change and delete objects. It’s\nas easy as registering your model in the admin site:
\nmysite/news/models.pyfrom django.db import models\n\nclass Article(models.Model):\n pub_date = models.DateField()\n headline = models.CharField(max_length=200)\n content = models.TextField()\n reporter = models.ForeignKey(Reporter, on_delete=models.CASCADE)\nmysite/news/admin.pyfrom django.contrib import admin\n\nfrom . import models\n\nadmin.site.register(models.Article)\nThe philosophy here is that your site is edited by a staff, or a client, or\nmaybe just you – and you don’t want to have to deal with creating backend\ninterfaces just to manage content.
\nOne typical workflow in creating Django apps is to create models and get the\nadmin sites up and running as fast as possible, so your staff (or clients) can\nstart populating data. Then, develop the way data is presented to the public.
\nA clean, elegant URL scheme is an important detail in a high-quality Web\napplication. Django encourages beautiful URL design and doesn’t put any cruft\nin URLs, like .php or .asp.
To design URLs for an app, you create a Python module called a URLconf. A table of contents for your app, it contains a simple\nmapping between URL patterns and Python callback functions. URLconfs also serve\nto decouple URLs from Python code.
\nHere’s what a URLconf might look like for the Reporter/Article\nexample above:
mysite/news/urls.pyfrom django.conf.urls import url\n\nfrom . import views\n\nurlpatterns = [\n url(r'^articles/([0-9]{4})/$', views.year_archive),\n url(r'^articles/([0-9]{4})/([0-9]{2})/$', views.month_archive),\n url(r'^articles/([0-9]{4})/([0-9]{2})/([0-9]+)/$', views.article_detail),\n]\nThe code above maps URLs, as simple regular expressions,\nto the location of Python callback functions (“views”). The regular expressions\nuse parenthesis to “capture” values from the URLs. When a user requests a page,\nDjango runs through each pattern, in order, and stops at the first one that\nmatches the requested URL. (If none of them matches, Django calls a\nspecial-case 404 view.) This is blazingly fast, because the regular expressions\nare compiled at load time.
\nOnce one of the regexes matches, Django calls the given view, which is a Python\nfunction. Each view gets passed a request object – which contains request\nmetadata – and the values captured in the regex.
\nFor example, if a user requested the URL “/articles/2005/05/39323/”, Django\nwould call the function news.views.article_detail(request,\n'2005', '05', '39323').
Each view is responsible for doing one of two things: Returning an\nHttpResponse object containing the content for the\nrequested page, or raising an exception such as Http404.\nThe rest is up to you.
Generally, a view retrieves data according to the parameters, loads a template\nand renders the template with the retrieved data. Here’s an example view for\nyear_archive from above:
mysite/news/views.pyfrom django.shortcuts import render\n\nfrom .models import Article\n\ndef year_archive(request, year):\n a_list = Article.objects.filter(pub_date__year=year)\n context = {'year': year, 'article_list': a_list}\n return render(request, 'news/year_archive.html', context)\nThis example uses Django’s template system, which has\nseveral powerful features but strives to stay simple enough for non-programmers\nto use.
\nThe code above loads the news/year_archive.html template.
Django has a template search path, which allows you to minimize redundancy among\ntemplates. In your Django settings, you specify a list of directories to check\nfor templates with DIRS. If a template doesn’t exist\nin the first directory, it checks the second, and so on.
Let’s say the news/year_archive.html template was found. Here’s what that\nmight look like:
mysite/news/templates/news/year_archive.html{% extends "base.html" %}\n\n{% block title %}Articles for {{ year }}{% endblock %}\n\n{% block content %}\n<h1>Articles for {{ year }}</h1>\n\n{% for article in article_list %}\n <p>{{ article.headline }}</p>\n <p>By {{ article.reporter.full_name }}</p>\n <p>Published {{ article.pub_date|date:"F j, Y" }}</p>\n{% endfor %}\n{% endblock %}\nVariables are surrounded by double-curly braces. {{ article.headline }}\nmeans “Output the value of the article’s headline attribute.” But dots aren’t\nused only for attribute lookup. They also can do dictionary-key lookup, index\nlookup and function calls.
Note {{ article.pub_date|date:"F j, Y" }} uses a Unix-style “pipe” (the “|”\ncharacter). This is called a template filter, and it’s a way to filter the value\nof a variable. In this case, the date filter formats a Python datetime object in\nthe given format (as found in PHP’s date function).
You can chain together as many filters as you’d like. You can write custom\ntemplate filters. You can write\ncustom template tags, which run custom\nPython code behind the scenes.
\nFinally, Django uses the concept of “template inheritance”. That’s what the\n{% extends "base.html" %} does. It means “First load the template called\n‘base’, which has defined a bunch of blocks, and fill the blocks with the\nfollowing blocks.” In short, that lets you dramatically cut down on redundancy\nin templates: each template has to define only what’s unique to that template.
Here’s what the “base.html” template, including the use of static files, might look like:
\nmysite/templates/base.html{% load static %}\n<html>\n<head>\n <title>{% block title %}{% endblock %}</title>\n</head>\n<body>\n <img src="{% static "images/sitelogo.png" %}" alt="Logo" />\n {% block content %}{% endblock %}\n</body>\n</html>\nSimplistically, it defines the look-and-feel of the site (with the site’s logo),\nand provides “holes” for child templates to fill. This makes a site redesign as\neasy as changing a single file – the base template.
\nIt also lets you create multiple versions of a site, with different base\ntemplates, while reusing child templates. Django’s creators have used this\ntechnique to create strikingly different mobile versions of sites – simply by\ncreating a new base template.
\nNote that you don’t have to use Django’s template system if you prefer another\nsystem. While Django’s template system is particularly well-integrated with\nDjango’s model layer, nothing forces you to use it. For that matter, you don’t\nhave to use Django’s database API, either. You can use another database\nabstraction layer, you can read XML files, you can read files off disk, or\nanything you want. Each piece of Django – models, views, templates – is\ndecoupled from the next.
\nThis has been only a quick overview of Django’s functionality. Some more useful\nfeatures:
\nA caching framework that integrates with memcached\nor other backends.
A syndication framework that makes\ncreating RSS and Atom feeds as easy as writing a small Python class.
More sexy automatically-generated admin features – this overview barely\nscratched the surface.
The next obvious steps are for you to download Django, read the\ntutorial and join the community. Thanks for your\ninterest!
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