One typical workflow in creating Django apps is to "create models and get the admin sites up and running as fast as possible", so your staff (or clients) can start populating data. Then, develop the way data is presented to the public.
object-relational mapper in which you describe your database layout in Python code data-model syntax
E.X.
from django.db import models
class Reporter(models.Model):
full_name = models.CharField(max_length=70)
def __str__(self):
return self.full_name
class Article(models.Model):
pub_date = models.DateField()
headline = models.CharField(max_length=200)
content = models.TextField()
reporter = models.ForeignKey(Reporter, on_delete=models.CASCADE)
def __str__(self):
return self.headline
Next, run the Django command-line utility to create the database tables automatically:
$ python manage.py migrate
you’ve got a free, and rich, Python API to access your data.
# Import the models we created from our "news" app
>>> from news.models import Reporter, Article
# No reporters are in the system yet.
>>> Reporter.objects.all()
<QuerySet []>
# Create a new Reporter.
>>> r = Reporter(full_name='John Smith')
# Save the object into the database. You have to call save() explicitly.
>>> r.save()
# Now it has an ID.
>>> r.id
1
# Now the new reporter is in the database.
>>> Reporter.objects.all()
<QuerySet [<Reporter: John Smith>]>
# Fields are represented as attributes on the Python object.
>>> r.full_name
'John Smith'
# Django provides a rich database lookup API.
>>> Reporter.objects.get(id=1)
<Reporter: John Smith>
>>> Reporter.objects.get(full_name__startswith='John')
<Reporter: John Smith>
>>> Reporter.objects.get(full_name__contains='mith')
<Reporter: John Smith>
>>> Reporter.objects.get(id=2)
Traceback (most recent call last):
...
DoesNotExist: Reporter matching query does not exist.
# Create an article.
>>> from datetime import date
>>> a = Article(pub_date=date.today(), headline='Django is cool',
... content='Yeah.', reporter=r)
>>> a.save()
# Now the article is in the database.
>>> Article.objects.all()
<QuerySet [<Article: Django is cool>]>
# Article objects get API access to related Reporter objects.
>>> r = a.reporter
>>> r.full_name
'John Smith'
# And vice versa: Reporter objects get API access to Article objects.
>>> r.article_set.all()
<QuerySet [<Article: Django is cool>]>
# The API follows relationships as far as you need, performing efficient
# JOINs for you behind the scenes.
# This finds all articles by a reporter whose name starts with "John".
>>> Article.objects.filter(reporter__full_name__startswith='John')
<QuerySet [<Article: Django is cool>]>
# Change an object by altering its attributes and calling save().
>>> r.full_name = 'Billy Goat'
>>> r.save()
# Delete an object with delete().
>>> r.delete()
Once your models are defined, Django can automatically create a professional, production ready administrative interface – a website that lets authenticated users add, change and delete objects. It’s as easy as registering your model in the admin site:
# mysite/news/models.py
from django.db import models
class Article(models.Model):
pub_date = models.DateField()
headline = models.CharField(max_length=200)
content = models.TextField()
reporter = models.ForeignKey(Reporter, on_delete=models.CASCADE)
# mysite/news/admin.py
from django.contrib import admin
from . import models
admin.site.register(models.Article)
you don’t want to have to deal with creating backend interfaces just to manage content.
A clean, elegant URL scheme is an important detail in a high-quality Web application.
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 mapping between URL patterns and Python callback functions.
- URLconfs also serve to decouple URLs from Python code.
# mysite/news/urls.py
from django.urls import path
from . import views
urlpatterns = [
path('articles/<int:year>/', views.year_archive),
path('articles/<int:year>/<int:month>/', views.month_archive),
path('articles/<int:year>/<int:month>/<int:pk>/', views.article_detail),
]
The code above maps URL paths to Python callback functions (“views”). The path strings use parameter tags to “capture” values from the URLs. When a user requests a page, Django runs through each path, in order, and stops at the first one that matches the requested URL. (If none of them matches, Django calls a special-case 404 view.) This is blazingly fast, because the paths are compiled into regular expressions at load time.
Once one of the URL patterns matches, Django calls the given view, which is a Python function. Each view gets passed a request object – which contains request metadata – and the values captured in the pattern.
For example, if a user requested the URL “/articles/2005/05/39323/”, Django would call the function news.views.article_detail(request, year=2005, month=5, pk=39323).
Each view is responsible for doing one of two things:
- Returning an HttpResponse object containing the content for the requested page
- raising an exception such as Http404
- The rest is up to you.
a view retrieves data according to the parameters, loads a template and renders the template with the retrieved data.
# mysite/news/views.py
from django.shortcuts import render
from .models import Article
def year_archive(request, year):
a_list = Article.objects.filter(pub_date__year=year)
context = {'year': year, 'article_list': a_list}
return render(request, 'news/year_archive.html', context)
# mysite/news/templates/news/year_archive.html
{% extends "base.html" %}
{% block title %}Articles for {{ year }}{% endblock %}
{% block content %}
<h1>Articles for {{ year }}</h1>
{% for article in article_list %}
<p>{{ article.headline }}</p>
<p>By {{ article.reporter.full_name }}</p>
<p>Published {{ article.pub_date|date:"F j, Y" }}</p>
{% endfor %}
{% endblock %}
Variables are surrounded by double-curly braces. {{ article.headline }} means “Output the value of the article’s headline attribute.” But dots aren’t used only for attribute lookup. They also can do dictionary-key lookup, index lookup and function calls.
Note {{ article.pub_date|date:"F j, Y" }} uses a Unix-style “pipe” (the “|” character). This is called a template filter, and it’s a way to filter the value of a variable. In this case, the date filter formats a Python datetime object in the given format.
Finally, Django uses the concept of “template inheritance”. That’s what the {% extends "base.html" %} does. It means “First load the template called ‘base’, which has defined a bunch of blocks, and fill the blocks with the following blocks.” In short, that lets you dramatically cut down on redundancy in templates: each template has to define only what’s unique to that template.
# mysite/templates/base.html
{% load static %}
<html>
<head>
<title>{% block title %}{% endblock %}</title>
</head>
<body>
<img src="{% static "images/sitelogo.png" %}" alt="Logo" />
{% block content %}{% endblock %}
</body>
</html>
Simplistically, it defines the look-and-feel of the site (with the site’s logo), and provides “holes” for child templates to fill. This makes a site redesign as easy as changing a single file – the base template.
It also lets you create multiple versions of a site, with different base templates, while reusing child templates. Django’s creators have used this technique to create strikingly different mobile versions of sites – simply by creating a new base template.