Django is a high-level Python Web framework that encourages rapid development and clean, pragmatic design. Built by experienced developers, it takes care of much of the hassle of Web development, so you can focus on writing your app without needing to reinvent the wheel. It’s free and open source. Following is the agenda of the meetup: 1. How to get started with Django 2. Advanced overview of Django components 1. Views 2. Models 3. Templates 4. Middlewares 5. Routing 3. Deep dive into Django ORM 4. How to write complex Django queries using Model Managers, Query Sets and Q library 5. How do Django models work internally Whether you're a newer Django developer wanting to improve your understanding of some key concepts, or a seasoned Djangonaut, there should be something for you.

1. DJANGO APPS AND ORM
PRODUCT VALLEY MEETUP GROUP BANGALORE (A PRODEERS CHAPTER)
- BY UDIT GANGWANI

2. ABOUT ME
I WEAR MULTIPLE HATS
SOFTWARE DEVELOPER
PRODUCT MANAGER
ENTREPRENEUR
I LOVE TO TRAVEL
MY FRIENDS CALL ME PIZZA MANIAC

3. WHAT WILL WE LEARN TODAY
INTRODUCTION TO DJANGO
HOW TO GET STARTED WITH DJANGO
COMPONENTS OF DJANGO FRAMEWORK
DJANGO MODELS, MODEL MANAGERS AND QUERY SETS
HOW DO DJANGO MODELS WORK

4. WHAT IS DJANGO ?
Django is a high-level Python Web framework that encourages rapid
development and clean, pragmatic design. Built by experienced developers, it
takes care of much of the hassle of Web development, so you can focus on
writing your app without needing to reinvent the wheel.
-- https://www.djangoproject.com/

5. WHY DJANGO ?
• Incredible programming language (Python)
• Perfect ORM for handling database
• Offers great control (Explicit is better than implicit)
• Django Admin GUI
• Simple and smaller footprint to get started
• Very big & active community
• Lots of Django packages for almost every functionality
• Support for large variants of Databases
• Django REST Framework

6. MTV ARCHITECTURE
Django follows MTV architecture:
M – Model
• app/models.py
V – View
• app/views.py
T – Templates
• app/templates/*.html
It is analogous to MVC architecture.
View in MVC corresponds to
Template in MTV
Controller in MVC corresponds to
View in MTV

7. POPULAR SITES BUILT WITH DJANGO
• Pinterest
• Instagram
• Discus
• Spotify
• Washington Post
• Firefox
• NASA
• BitBucket
• Prezi
• EventBrite

8. DJANGO SETUP AND A DEMO

9. ENVIRONMENT SETUP
• Standard Environment
• Common environment and set of packages for each project on your system
• Virtual Environment
• Isolated environment for each Django project
• No limits on the number of environments
• Can have different python version for each project
• Using virtualenv or pyenv

10. STEPS TO SETUP VIRTUAL ENVIRONMENT
• pip install virtualenv
• virtualenv .app
• source appbinactivate

11. GETTING STARTED WITH DJANGO
• Install Django using pip
• Create a project using django-admin
• Create your database
• Configure DB settings in settings.py
• Define your models
• Add external modules
• Write your Templates
• Define your Urls
• Write your Views and bind them to Urls
• Test application
• Deploy application using NginX or Apache

12. DJANGO PROJECT STRUCTURE
• Each Django app is a Python Package
• Each app contains one or more Python
modules (files of python code)
• To form a package every app directory
must contain an __init__.py file

13. BLOG APPLICATION DEMO

14. DJANGO COMPONENTS

15. URL’S DISPATCHER/ROUTING
• Django determines the root URLconf module to use
• Django loads the Python module and looks for the variable urlpatterns
• Django runs through each pattern and stops at the one which matches
• Once the regex matches, Django calls the given View

16. VIEWS
• A Django view is a callable which takes a request and returns a response

17. MODELS & MODEL FIELDS
• Each model maps to a single database table.
• Each model is a Python class that subclasses django.db.models.Model
• Each attribute of the model represents a database field

18. TEMPLATES
• A template contains the static parts of the desired HTML output as well as
some special syntax describing how dynamic content will be inserted

19. MIDDLEWARES
• Middleware is a framework of hooks into Django’s request/response
processing. It’s a light, low-level “plugin” system for globally altering
Django’s input or output.

20. DJANGO MODELS

21. MIGRATIONS
• Migrations are Django’s way of propagating changes you make to your
models (adding a field, deleting a model, etc.) into your database schema.
• They’re designed to be mostly automatic
Thereareseveralcommandswhichyouwilluse tointeractwithmigrations:
•migrate,whichisresponsibleforapplyingmigrations,aswellas unapplyingandlistingtheirstatus.
•makemigrations,whichisresponsibleforcreatingnewmigrationsbasedonthechangesyouhavemadetoyourmodels.
•sqlmigrate,whichdisplaystheSQLstatementsforamigration.
•showmigrations,whichlistsaproject’smigrations.

22. MODEL RELATIONSHIPS
Many to One Relationships Many to Many Relationships
One to One Relationships

23. MODEL QUERIES
• Creating Objects
• Retrieving Objects
• Create query set objects using your model manager. A query set represents the
collection of objects from database
• Query sets are lazy
• Retrieving specific objects using filters

24. MODEL QUERIES ON RELATED OBJECTS
One to Many Field
One to One Many Reverse lookup
Many to Many Field
One to One Field

25. MANAGERS
• A Manager is the interface through which database query operations are
provided to Django models. At least one Manager exists for every model in a
Django application.
• Adding extra Manager methods is the preferred way to add “table-level”
functionality to your models. (For “row-level” functionality – i.e., functions
that act on a single instance of a model object – use Model methods, not
custom Manager methods.)

26. MANAGERS EXAMPLE

27. QUERY SETS
• Internally, a QuerySet can be constructed, filtered, sliced, and generally
passed around without actually hitting the database. No database activity
actually occurs until you do something to evaluate the queryset.
• Important methods that return new Query set
• filter(), exclude(), annotate(), order_by(), reverse(), distinct(), values(), all()
• Important methods that do not return Query set
• get(), create(), update(), aggregate(), iterator(), count()

28. Q OBJECTS
• A Q object (django.db.models.Q) is an object used to encapsulate a
collection of keyword arguments. It is used to execute more complex queries
(for example, queries with OR statements)

29. AGGREGATION
Aggregation for entire table
Aggregation for each item
in table

30. HOW DO DJANGO MODELS WORK ?

31. HOW DO MODELS WORK - METACLASSES
Lets understand what goes on from the time a model is imported until an
instance is created by the user.
Lets look at an example model

32. HOW DO MODELS WORK - METACLASSES
So ModelBase.__new__ is called to create this new Example class. It is important to realise that we are
creating the class object here, not an instance of it
The Model class (see base.py) has a __metaclass__ attribute that defines ModelBase (also in base.py) as
the class to use for creating new classes.
The __new__ method is required to return a class object that can then be instantiated (by calling
Example() in our case).
A new class object with the Example name is created in the right module namespace. A _meta attribute
is added to hold all of the field validation, retrieval and saving machinery

33. HOW DO MODELS WORK - METACLASSES
Each attribute is then added to the new class object. Putting this in the context of our example, the
static and __unicode__ attributes would be added normally to the class as a string object and unbound
method, respectively.
In case of Field, it does not add the new attribute to the class we are creating (Example). Instead it adds
itself to the Example._meta class, ending up in the Example._meta.fields list
The ModelBase._prepare method is called. This sets up a few model methods that might be required
depending on other options you have selected and adds a primary key field if one has not been explicitly
declared.
The registration is done right at the end of the ModelBase.__new__ method. The register_models()
function in loaders.py

34. REFERENCES
• Django Orm at Django under the hood: https://www.youtube.com/watch?v=CGF-0csOjPw
• Django Topics: https://docs.djangoproject.com/en/1.9/topics/
• What is a MetaClass in Python: http://stackoverflow.com/questions/100003/what-is-a-
metaclass-in-python
• How do Django Models work:
• http://stackoverflow.com/questions/12006267/how-do-django-models-work
• https://code.djangoproject.com/wiki/DevModelCreation
• Django Cookbook: https://code.djangoproject.com/wiki/CookBook
• Python3 Cookbook: http://python3-
cookbook.readthedocs.io/zh_CN/latest/c09/p18_define_classes_programmatically.html

35. REFERENCES
• Try Django Blog Project:
• https://github.com/codingforentrepreneurs/try-django-19
• https://www.codingforentrepreneurs.com/projects/try-django-19/
• Django Models and Migrations:
• http://www.webforefront.com/django/setupdjangomodels.html
• Making Django Queries :
• https://docs.djangoproject.com/en/1.9/topics/db/queries/
• Understanding Django Model Managers and QuerySets:
• https://docs.djangoproject.com/en/1.9/ref/models/querysets/
• https://docs.djangoproject.com/en/1.9/topics/db/managers/

36. THANK YOU