Introduction Django

Introduction to Django
pyArkansas

Wade Austin
@k_wade_a

What is Django?
“Django is a high-level Python Web framework that
encourages rapid development and clean, pragmatic
design.”
www.djangoproject.com

• Created out of the newspaper industry
• Help developers build sites fast
• Encourage Reuse and Lose Coupling
• DRY (don’t repeat yourself)
• Minimal Code
• Opinionated

Batteries Included
django.contrib

• Admin Interface for editing data.
• Auth module for user accounts
• Syndication module for generation of RSS
• Static Pages

Active Community

• Many Community Contributed Apps
• Pinax
http://pinaxproject.com/

• Django Packages
http://djangopackages.com/

Django Projects
• A project is your website.

• Projects contain the configuration information for
your site.

• Create a project:
django-admin.py startproject [PROJECT_NAME]

• Projects contain 3 files:
• settings.py - configuration information for your project

• urls.py - URL routes defined by your project

• manage.py - alias of django-admin.py tuned to your project

Django Applications
• Projects are built from Applications
• Apps encapsulate some piece of
functionality
• blog, photo gallery, shopping cart, etc.

• Apps can be reused
• Apps are Python Packages
• manage.py startapp [MY_APP_NAME]

Django Application
Components
• Models - Your Data
• Views - Rules for Accessing Data
• Templates - Displays Data
• URL Patterns - Maps URLs to Views

Models

• Describes the data in your apps
• Deﬁned in an app’s models.py ﬁle
• Map Python Classes to Database Tables
• Provides an API for creating, retrieving,
changing and deleting data

Blog Data Deﬁnition
CREATE TABLE "blog_category" (
"id" integer NOT NULL PRIMARY KEY,
"name" varchar(50) NOT NULL
);

CREATE TABLE "blog_blogpost" (
"id" integer NOT NULL PRIMARY KEY,
"title" varchar(100) NOT NULL,
"slug" varchar(50) NOT NULL UNIQUE,
"publish_date" datetime NOT NULL,
"is_published" bool NOT NULL,
"content" text NOT NULL,
"category_id" integer NOT NULL REFERENCES "blog_category" ("id")
);

Django Hides the SQL

• SQL is not consistent across databases
• Difﬁcult to store in version control

Model Example
from django.db import models
from datetime import datetime

class Category(models.Model):
name = models.CharField(max_length=50)

class BlogPost(models.Model):
title = models.CharField(max_length=100)
slug = models.SlugField(unique=True)
publish_date = models.DateTimeField(default=datetime.now)
is_published = models.BooleanField(default=False)
content = models.TextField(blank=True)
category = models.ForeignKey(Category,
related_name=‘posts’)

Creating your database

• manage.py syncdb command creates tables
from models
• Creates all models for any app in your
project’s INSTALLED_APPS setting

Querying Models
posts = BlogPost.objects.all()

publshed_posts = BlogPost.objects.filter(is_published=True)

news_posts = BlogPost.objects.filter(category__name = 'News')

c = Category(
name="News"
)
c.save()

Views

• Business Logic
• Perform a task and render output
(HTML/JSON/XML)

• Python function that takes an HttpRequest
and returns an HttpResponse
• Deﬁned in an app’s views.py ﬁle

Hello World View

from django.http import HttpResponse

def hello_world(request):
return HttpResponse("Hello World")

Latest Posts View
from django.shortcuts import render
from blog.models import BlogPost

def get_latest_posts(request):
today = datetime.datetime.now()
posts = BlogPost.objects.filter(is_published=True).
filter(publish_date__lte=today).
order_by('-publish_date')

return render( request, 'blog/latest_posts.html',
{'posts':posts})

Post Detail View
from django.shortcuts import render, get_object_or_404
from blog.models import BlogPost

def blog_post_detail(request, slug):
post = get_object_or_404(BlogPost, slug=slug)
return render( request, "blog/blogpost_detail.html",
{"post":post})

URL Routes

• Defines the URLs used in your project
• Maps a URL to a View Function
• Defined using Regular Expressions
• Defined in an app’s urls.py file.

URL Example

urlpatterns = patterns('',
url(r'^latest_posts/$',
'blog.views.get_latest_posts',
name='blog_blogpost_latest'),

url(r'^post/(?P<slug>[-w]+)/$',
'blog.views.blog_post_detail',
name='blog_blogpost_detail'),
)

Templates
• Describes the Presentation of your data
• Separates Logic from Presentation
• Simple Syntax
• Designer Friendly
• Supports Reuse through inheritance and
inclusion
• Blocks allow child templates to insert
content into parent templates

Template Syntax

• Variables: {{variable-name}}
• Tags: Perform logic
{% include “_form.html” %}
• Filters: Operate on data
{{post.publish_date|date:"m/d/Y"}}

Template “base.html”
<html>
<head>
<title>{% block title %}{% endblock %}My Site</title>
<link rel="stylesheet" href="{{STATIC_URL}}css/screen.css"
media="screen, projection"/>
</head>
<body>
<h1>My test site</h1>

{% block content %}
{% endblock %}

</body>
</html>

Template
“latest_posts.html”
{% extends "base.html" %}

{% block title %}Latest Blog Posts -
{% endblock %}

{% block content %}
<h2>Latest Blog Posts</h1>
{% for p in posts %}
<h3><a href="{% url blog_blogpost_detail p.slug %}">{{p.title}}</a></h3>
<p><strong>Published:</strong>
{{p.publish_date|date:"m/d/Y"}}
</p>
<div class="content">
{{p.content|safe}}
</div>
{% endfor %}
{% endblock %}

List of Template Tags and Filters: https://docs.djangoproject.com/en/dev/ref/templates/builtins/

The admin
• Not a CMS
• Allows site admins to edit content
• Auto CRUD views for your models
• Easy to customize
• Optional. If you don’t like it you can write
your own

The admin

• add django.contrib.admin to
INSTALLED_APPS
• Uncomment admin import, discover, and url
pattern from PROJECTS urls.py
• Create an admin.py ﬁle for each app you
want to manage

Sample admin.py

from django.contrib import admin

class BlogPostAdmin(admin.ModelAdmin):
list_display = ('title', 'publish_date', 'is_published')
list_filter = ('is_published', 'publish_date')
search_fields = ('title', 'content')

admin.site.register(BlogPost, BlogPostAdmin)

Other Stuff

• Forms
• Caching
• Testing

Resources
• Ofﬁcial Django Tutorial
https://docs.djangoproject.com/en/dev/intro/tutorial01/

• Django Documentation
https://docs.djangoproject.com/

• The Django Book
http://www.djangobook.com/

• Practical Django Projects
https://docs.djangoproject.com/

• Pro Django
http://prodjango.com/

Thank You

Wade Austin
http://wadeaustin.com
@k_wade_a

Introduction Django

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