A Basic Django Introduction

Web Development With Django

A Basic Introduction

Ganga L

Python Frameworks

 Django
 CherryPy
 Pylons
 Flask
 Bottle
 Tipfy
 Pyramid
 Cubic Web
 GAE framework

Outline

 What Is Django?
 Project Structure
 Data Handling
 The Admin Interface
 Django Forms
 Views
 Templates

What Is Django?

 High-level framework for rapid web development
 Complete stack of tools
 Data modelled with Python classes
 Production-ready data admin interface, generated dynamically
 Elegant system for mapping URLs to Python code
 Generic views’ to handle common requests
 Clean, powerful template language
 Components for user authentication, form handling, caching . . .

Creating Projects & Apps

 Creating a project:
django-admin.py startproject mysite
 Creating an app within a project directory:
cd mysite
./manage.py startapp poll

Project Structure

 A Python package on your PYTHONPATH
 Holds project-wide settings in settings.py
 Holds a URL configuration (URLconf) in urls.py
 Contains or references one or more apps

App

 A Python package on your PYTHONPATH
(typically created as a subpackage of the project itself)
 May contain data models in models.py
 May contain views in views.py
 May have its own URL configuration in urls.py

Up & Running

 Set PYTHONPATH to include parent of your project directory
 Define new environment variable DJANGO_SETTINGS_MODULE,

setting it to project settings (mysite.settings)
 3 Try running the development server:
/manage.py runserver

Creating The Database

 Create database polls in youe database
 Sync installed apps with database:
./manage.py syncdb

Create Project

 Create Project mysite
mysite/
manage.py
mysite/
__init__.py
settings.py
urls.py

Create Application

 python manage.py startapp polls
polls/
__init__.py
models.py
tests.py
views.py

Create Models

from django.db import models

class Poll(models.Model):
question = models.CharField(max_length=200)
pub_date = models.DateTimeField('date published')

class Choice(models.Model):
poll = models.ForeignKey(Poll)
choice_text = models.CharField(max_length=200)
votes = models.IntegerField(default=0)

The Data Model

 A description of database layout, as a Python class
 Normally represents one database table
 Has fields that map onto columns of the table
 Many built-in field types
 CharField, TextField
 IntegerField, FloatField, DecimalField
 DateField, DateTimeField, TimeField
 EmailField, URLField
 ForeignKey . . .

Installed App

INSTALLED_APPS = (
'django.contrib.admin',
'django.contrib.auth',
'django.contrib.contenttypes',
'django.contrib.sessions',
'django.contrib.messages',
'django.contrib.staticfiles',
'polls',
)

python manage.py syncdb

Registering Models in Admin

 In admin.py in the Poll app:

from django.contrib import admin
from mysite.polls.models import Poll

admin.site.register(Poll)

In urls.py:

from django.conf.urls import patterns, include, url

admin.autodiscover()

urlpatterns = patterns('',
url(r'^admin/', include(admin.site.urls)),
)

Generic Views

 Provide ready-made logic for many common tasks:
 Issuing a redirect
 Displaying a paginated list of objects
 Displaying a ‘detail’ page for a single object
 Yearly, monthly or daily listing of date-based
objects
 ‘Latest items’ page for date-based objects
 Object creation, updating, deletion (with/without
authorisation)

Generic Views Example

 views.py
def index(request):
return HttpResponse("Hello, world. You're at the poll index.")
 Url.py
from django.conf.urls.defaults import *
from polls import views

url(r'^$', views.index, name='index')
)
 Main URL.py
from django.conf.urls import patterns, include, url

admin.autodiscover()

url(r'^polls/', include('polls.urls')),
url(r'^admin/', include(admin.site.urls)),
)

Creating & Saving Objects

 Invoke constructor and call save method:
 call create method of Club model manager:

poll = Poll(question='what is your DOB? ', year='1986)
poll.save()

Poll.objects.create(question='what is your DOB? ', year='1986)

View Function

 Takes an HTTPRequest object as a parameter
 Returns an HTTPResponse object to caller
 Is associated with a particular URL via the URLconf

HTTP Response

from datetime import date
from django.http import HttpResponse

def today(request):
html = '<html><body><h2>%s</h2></body></html>' % date.today()
return HttpResponse(html)

from django.shortcuts import render_to_response
From mysite.polls.models import Poll

def poll_details(request):
today = date.today()
poll_data = Poll.objects.all()
return render_to_response('clubs.html', locals(), context_instance =
RequestContext(request))

Templates

 Text files containing
 Variables, replaced by values when the template
is rendered[
 {{ today }}
 Filters that modify how values are displayed
 {{ today|date:"D d M Y" }}
 Tags that control the logic of the rendering
process
 {% if name == "nick" %}
 <p>Hello, Nick!</p>
 {% else %}
 <p>Who are you?</p>
 {% endif %}

Template Example

settings.py

TEMPLATE_DIRS = (
os.path.join(os.path.dirname(__file__), 'templates'),
)

templates/club/club_list.html

{% extends "base.html" %}
{% block title %}Clubs{% endblock %}
{% block content %}
<h1>Clubs</h1>
<ol>
{% for club in clubs %}
<li>{{ club }}</li>
{% endfor %}
</ol>
{% endblock %}

Django Forms

 A collection of fields that knows how to validate itself and display
itself as HTML.
 Display an HTML form with automatically generated form widgets.
 Check submitted data against a set of validation rules.
 Redisplay a form in the case of validation errors.
 Convert submitted form data to the relevant Python data types.

Django Model Forms

from django.forms import ModelForm
import mysite.polls.models import Poll

class PollForm(ModelForm):
class Meta:
model = Pole

Summary

 We have shown you
 The structure of a Django project
 How models represent data in Django applications
 How data can be stored and queried via model
instances
 How data can be managed through a dynamic
admin interface
 How functionality is represent by views, each
associated
with URLs that match a given pattern
 How views render a response using a template

A Basic Django Introduction

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