Day 4: Introduc/on to Django | Django Model Syntax

Day 4: Introduc/on to Django

GSL South Africa 2015

Today’s Agenda

•  The Big Picture •  Django – A Web Applica/on Framework •  Your First Django App •  Models in Django •  Today’s Assignment

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The Big Picture


Once upon a /me…

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OR


Nowadays…

OR OR


Implemen/ng the Backend

We need to implement the backend: •  A web applica/on framework, like – MonoRail, CppCMS, Apache Click, Grails, Spring, Stripes, mul/ple, Catalyst, CakePHP, Drupal, Symfony, CherryPy, Django, web2py, Ruby on Rails, Compujure

•  A host, like – Heroku, Google App Engine

•  A RESTful API to communicate with frontend

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Web Applica/on Framework

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•  A framework (code libraries) to help you make web applica/ons or websites

•  Supports you with – Handling HTTP requests – Templates for common HTML layouts – URL mapping – Database communica/on – Session management – Site security


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Django Web Applica/on Framework

Why Django?


Why Django?

•  Fast and easy development of web applica/ons – Modular and re-‐useable. Don’t Repeat Yourself (DRY) principle

– Built-‐in database management

•  Ac/ve development and wide community support

•  Supported by Google App Engine & Heroku

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Django vs. PHP


PHP SELECT Statement


Django SELECT Statement

Django Architecture


Model-‐View-‐Controller (MVC)

•  A pacern for organizing code oeen seen in web app frameworks

•  Main idea: 1.  Separate storage and manipula/on of data (model)

from presenta/on of data (view) 2.  Controller communicates between model and view

•  Advantages – Develop and test model and view independently –  Easier for others to understand (modularity)

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Model-‐View-‐Controller (MVC) (news site example)

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Controller

View Model

•  News stories and images in a database

•  User comments

•  Layout of stories on mobile phone or desktop browser

Send request for a story

Asks the model for the story and its user comments

Serves requested story


Model-‐Template-‐View

In Django: Model-‐Template-‐View (similar to MVC pacern)

•  Model – describes database informa/on

•  Template – decides how to present informa/on

•  View – manages what informa/on to output based on request

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Model-‐Template-‐View

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View

Template Model

Send request for data

Asks the model for data

Provide Database Informa/on UI Layout Communicate

with Database

Handles Informa/on Exchange

Model


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Your First Django App


Programming Interface

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Terminal / Command Prompt Python IDLE or Favorite editor


New Project

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Project Structure: Whole project in one folder (mysite)

•  MySite Python package •  Applica/ons (polls) •  (Database) •  manage.py

•  Use for interac/on with your project

•  MySite Python Package •  __init__.py •  sejngs.py •  urls.py •  wsgi.py


First Django Setup

Aeer a couple commands in terminal...

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Models

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Models

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View

Template Model

Send request for data

Asks the model for data

Provide Database Informa/on UI Layout Communicate

with Database

Handles Informa/on Exchange


What is a Model

•  Python class describing data in your applica/on – Subclass of models.Model

•  Assigns acributes to each data field •  Avoid direct work with the database – No need to handle database connec/ons, /meouts, etc. – Let Django do it for you!

– Provides Schema for database

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Django Model Syntax

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Import statements

SubClass of models.Model Class

Define fields

Can define more func/ons

__unicode__ corresponds to python __str__


Django Fields

We can define fields directly in our model class – No need to define manually in database

Example: create two fields in our Poll class

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Define Type of Field •  E.g. models.CharField

Define arguments of field •  E.g. max_length=200

Django will automa/cally create fields in database


Important Django Field Types •  BooleanField

–  Checkbox •  CharField(max_length)

–  Single-‐line textbox •  DateField

–  Javascript calendar •  DateTimeField

–  Javascript calendar, /me picker •  DecimalField(max_digits, decimal_places)

–  Decimal numbers •  EmailField

–  Charfield that validates email address

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•  FileField •  File upload, stores path

in database •  FloatField

•  Floa/ng point numbers •  IntegerField

Integer textbox •  Posi/veIntegerField

•  Integer textbos for posi/ve integers

•  TextField •  Mul/-‐line textbox


Rela/onships

•  Clearly, the power of rela/onal databases lies in rela/ng tables to each other. Django offers ways to define the three most common types of database rela/onships: many-‐to-‐one, many-‐to-‐many and one-‐to-‐one.


Rela/onship Examples: Many-‐to-‐One

•  A Car has a Manufacturer, but a Manufacturer can have many Cars


Rela/onship Examples: Many-‐to-‐Many

•  A Pizza can have mul/ple Toppings. Each type of Topping can be on mul/ple Pizzas


Rela/onship Examples: Many-‐to-‐Many •  Some/mes you need to associate data with the rela/onship between a Many-‐to-‐Many.


Rela/onship Examples: One-‐to-‐One


Rules of Django Models •  When you update a model, ALWAYS RUN python manage.py migrate

•  All classes extend models.Model •  Models only live in Apps •  Django doesn't save objects un/l you call save() method

>>>a1 = Album(...) # a1 is not saved to the database yet! >>>a1.save() # Now it is.

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Today’s Assignment

Get started with Django! –  If you haven’t already, install Django 1.8 –  Create your first Django app:Wri/ng your first Django App – Part 1

Wri/ng your first Django App – Part 2 –  Come up with preliminary data model for you project

Helpful Documenta/on: – Models sec/on of Django docs

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Documents

Day 4: Introduc/on to Django | Django Model Syntax