Tango with django

Programming Languages
Popular
Programming Languages > 500
Frameworks > 90000
at least what Wikipedia says
What Really I should Learn ?
2

Lets go back & check last software you developed
• Without Alternatives, how difficult it was to estimate ?
• Ideas -> Conceptualization -> Enterprise Ready was full of Effort, Pain,
Time waste, Complexity & Change !!!
• Was my system adaptive to the change that business demand? … God
it was really nightmare to maintain the code ….
• What is the time it took to get the customer from a frustrated to a happy
customer ? also the time it took to develop version 2, with different
requirements & scale:
3

Time is an essence
Python : Django A complete framework
A Web Framework that shortens the Time it takes to develop
software in at least an Order of Magnitude. while also
tremendously minimizing Effort Pain, Time waste, Complexity,
Cost of change & more
9/1/2014 4

Python: Language of Best
• By The organizations attracting the best Programmers
in the world
Google, NASA, MIT
5

• “The framework for perfectionists
with deadlines”
• Model-Template-View ( MTV ) not as
complex as MVC
• Flexible template language that can
be used to generate HTML, CSV,
Email or any other format
• Includes ORM that supports many
databases – Postgresql, MySQL,
Oracle, SQLite
• Lots of extras included –
middleware, csrf protections,
sessions, caching, authentication
• Written in C – high
performance, ability to link to
C libraries for extensions
• Interpreted script language
compiled on the fly into byte
code
• Easier to read coding
standards – whitespace
sensitive
• Object Oriented
WHY
6

Scalability
• Django runs on regular web servers, such as
Apache, Lighty or Nginx, using a built-in Python
or WSGI adapter
• This makes it very lightweight & scalable, as any
LAMP deployment
o There are examples of sites that handle MM reqs/hour, using less
than 10 servers
7

IT Acceptance
• IT environments today are mostly familiar with
Java
• Solution: use Jython that compiles Python to
bytecode
o Package a Django project as .war
o Sun constantly improves Jython & maintains compatibility /w
Django
8

Project File Structure
django-admin.py startproject
<PROJECT_ROOT>
manage.py
<PROJECT_DIR>
__init__.py
settings.py
urls.py
wsgi.py
10

settings.py
• Defines settings used by a Django application
• Referenced by wsgi.py to bootstrap the project
loading
• Techniques for managing dev vs prod settings:
o Create settings-dev.py and settings-prod.py and use symlink to link
settings.py to the correct settings
o Factor out common settings into base-settings.py and import. Use
conditionals to load correct settings based on DEBUG or other setting
11

Sample Settings…
DEBUG = True
TEMPLATE_DEBUG = True
ALLOWED_HOSTS = []
# Application definition
INSTALLED_APPS = (
'django.contrib.admin',
'django.contrib.auth',
'django.contrib.contenttypes',
'django.contrib.sessions',
'django.contrib.messages',
'django.contrib.staticfiles',
)
12

Django Apps
• Reusable modules
• django-admin.py startapp <app_name>
• Creates stub layout:
<APP_ROOT>
admin.py
models.py
templates (directory)
tests.py
views.py
urls.py
13

Django Models
• Defined in models.py
• Typically inherit from django.db.models.Model
Example Model:
from django.db import models
class TestModel(models.Model):
name = models.CharField(max_length = 20)
age = models.IntegerField()
14

Models (cont’d)
• Default is to set NOT NULL on all fields. Override by
adding null = True to field definition:
name = models.CharField(max_length=20, null =
True)
• Relationships defined through special field types:
models.OneToOneField(model)
models.ForeignKey(model)
models.ManyToManyField(model)
15

Models (cont’)
• Need Nulls in a Boolean Field? Use
models.NullBooleanField()
• Set Default value with “default”:
count = models.IntegerField(default = 0)
• Use a inner Meta class to define additional options,
especially useful for abstract classes:
class TestModel(models.Model):
class Meta:
abstract = True
16

Model Methods
• model.save(self, *args, **kwargs)
• model.delete(self, *args, **kwargs)
• model.get_absolute_url(self)
• model.__str__(self) [Python 3]
model.__unicode__(self) [Python 2]
• Override with super(MODEL, self).save(*args,
**kwargs)
17

Activating a Model
• Add the app to INSTALLED_APPS in settings.py
• Run manage.py validate
• Run manage.py syncdb
• Migrations
o Write custom script or manually handle migrations
o Use South
18

Selecting Objects
• Models include a default manager called objects
• Manager methods allow selecting all or some
instances
Question.objects.all()
Question.objects.get(pk = 1)
Use try block, throws DoesNotExist
exception if no match
Question.objects.filter(created_date__lt = ‘2014-
01-01’)
• Returns QuerySet
19

Introspecting Legacy
Models
• manage.py inspectdb
• Cut and paste generated code into models.py –
Easy!!
20

Full Sample
from datetime import datetime
class TimestampedModel(models.Model):
created_datetime = models.DateTimeField()
updated_datetime = models.DateTimeField()
def save(self, *args, **kwargs):
if self.id is None:
self.created_datetime = datetime.now()
updated_datetime = datetime.now()
super(TimestampedModel,self).save(*args, **kwargs)
class Meta:
abstract = True
21

Full Sample (cont’d)
class Question(TimestampedModel):
question_text = models.CharField(max_length = 200)
def __str__(self):
return self.question_text
22

Function vs. Class Views
• Django allows two styles of views – functions or class
based views
• Functions – take a request object as the first
parameter and must return a response object
• Class based views – allow CRUD operations with
minimal code. Can inherit from multiple generic
view classes (i.e. Mixins)
23

Sample – Viewing a List
of Questions
• Function based:
from .models import Question
from django.shortcuts import render_to_response
def question_list(request):
questions = Question.objects.all()
return render_to_response(‘question_list.html’, {
‘questions’:questions})
24

Quick CRUD Operations
with Generic Views
• ListView
• UpdateView
• CreateView
• If Model is specified, automagically creates a
matching ModelForm
• Form will save the Model if data passes validation
• Override form_valid() method to provide custom
logic (i.e sending email or setting additional fields)
25

Sample – As Class Based
View
from django.views.generic import ListView
class QuestionList(ListView):
model = Question
context_object_name = ‘questions’
26

Django Templates
• Very simple syntax:
variables = {{variable_name}}
template tags = {%tag%}
• Flexible – can be used to render html, text, csv,
email, you name it!
• Dot notation – template engine attempts to resolve
by looking for matching attributes, hashes and
methods
27

Question List Template
<!doctype html>
<html lang=en>
<head>
<meta charset=utf-8>
<title>List of Questions</title>
</head>
<body>
{%if questions%}
<ul>
{%for q in questions%}
<li>{{q.question_text}}</li>
{%endfor%}
</ul>
{%else%}
<p>No questions have been defined</p>
{%endif%}
</body>
</html>
28

urls.py
• Defines routes to send urls to various views
• Can use regular expressions
• Extract parameters from a url and pass to the view
as a named parameter:
r(‘^question/(?P<question_id>d+)/$’,’views.question_
detail’)
• Extensible – urls.py can include additional url files
from apps:
r(‘^question/’,include(question.urls))
29

Forms in Django
• django.forms provides a class to build HTML forms
and validation. Example:
from django import forms
class EditQuestionForm(forms.Form):
question_text = forms.CharField(max_length = 200)
• Often redundant when creating forms that work on
a single model
30

ModelForms
• Automatically generate a form from a model.
• Handles saving a bound model
• Can specify fields to be included or excluded in the
form
• Sample:
from django.forms import ModelForm
class QuestionForm(ModelForm):
class Meta:
model = Question
fields = [‘question_text’]
31

Using a ModelForm
• Create an instance of an empty form:
form = QuestionForm()
• Create a form to update an existing instance of a
model:
question = Question.objects.get(pk = 1)
form = QuestionForm(instance = question)
• Pass the form into the template and use the form
methods to render the form:
form.as_p
form.as_ul
form.<field_name>
form.<field_name>.errors
32

Request & Response
• Request object encapsulate the request and provide
access to a number of attributes and methods for
accessing cookies, sessions, the logged in user object,
meta data (i.e environment variables),
• Response objects are returned to the browser. Can set
content type, content length, response does not have
to return HTML or a rendered template
• Special response types allow for common functionality:
HttpResponeRedirect
Http404
HttpStreamingResponse
33

Django Extras
• CRSF Middleware – enabled by default. Include
template tag in all forms:
{%csrf_token%}
• Authentication
• Caching
• Sessions
• Messages
• Email
• Logging
34

Auth Decorators
• Live in django.contrib.auth.decorators
• login_required
@login_required
def function_view(request):
….
• user_passes_test (can be used with lambda
functions for real power) –
@user_passes_test(lambda u: u.is_staff)
def function_view(request):
…
• has_perms – test for user permissions
35

Demo: 30 mins
Let’s develop an Release Tracking system
o Create Business Data Model
o Database CRUD Operations to manage/add/edit/delete Releases
o Rich Web UI (search, filters, last actions)
o Users management (permissions, groups), User logging, Access level
control
o Scalable deployment (any # of users)
36

Step1: Settings: Connect to
Database
• DATABASES = {
• 'default': {
• 'ENGINE': 'django.db.backends.mysql', # Add 'postgresql_psycopg2', 'mysql', 'sqlite3' or 'oracle'.
• 'NAME': ‘release', # Or path to database file if using sqlite3.
• # The following settings are not used with sqlite3:
• 'USER': 'root',
• 'PASSWORD': ‘',
• 'HOST': 'localhost', # Empty for localhost through domain sockets or '127.0.0.1' for localhost through TCP.
• 'PORT': '', # Set to empty string for default.
• }
• }
37

Step2: Data Model
class Environment(models.Model):
environment = models.CharField(null=False, max_length=200)
# Create your models here.
class Release(models.Model):
dateCreated = models.DateField(null=False, auto_now_add=True)
releaseDate = models.DateField(null=False)
releaseTitle = models.CharField(null=False, max_length=200)
releaseEnv = models.ForeignKey(Environment)
38

Step3: Sync DB
django_manage.py syncdb
Whoooo ---- Your DB tables are created
What Next  Lets create some Interfaces
39

Register Admin
from django.contrib import admin
class Environment(models.Model):
environment = models.CharField(null=False, max_length=200)
# Create your models here.
class Release(models.Model):
dateCreated = models.DateField(null=False, auto_now_add=True)
releaseDate = models.DateField(null=False)
releaseTitle = models.CharField(null=False, max_length=200)
releaseEnv = models.ForeignKey(Environment)
admin.site.register(Release)
admin.site.register(Environment)
40

Admin Interface Ready
• Run  manage.py runserver 8000
http://127.0.0.1:8000/admin/
- Entire CRUD Operation for
Models
- User Authentication, Groups,
Access Level & control
- User Log
- Multisite & Multi Application
41

Views: Front End
• Setup a URL pattern : Edit url.py
url(r'^$', 'ReleaseTracker.views.home', name='home'),
. Create view as home
# Create your views here.
from django.http import HttpResponse
from rtracker.models import Environment
from rtracker.models import Release
from django.shortcuts import get_object_or_404, render_to_response
from django.template import RequestContext
def home(request):
releaseitems = Release.objects.all()
return render_to_response('home.html', {'releaseitems': releaseitems},
context_instance=RequestContext(request))
42

Create Template
Create home.html in templates
<!DOCTYPE html>
<html>
<head>
<title></title>
</head>
<body>
{# you can include templates #}
{% include "nav.html" %}
{% for release in releaseitems %}
{{release.releaseTitle}}
{% endfor %}
</body>
</html>
43

FRONT END
• Open http://127.0.0.1:8000/
You will be able to see the model data
44

Tango with django

More Related Content

What's hot (20)

Similar to Tango with django (20)

More from Rajan Kumar Upadhyay (8)

Recently uploaded (20)

Tango with django