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
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Once upon a me…
OR
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Nowadays…
OR OR GSL South Africa 2015
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
• 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
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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 GSL South Africa 2015
PHP SELECT Statement GSL South Africa 2015
Django SELECT Statement Django Architecture GSL South Africa 2015
Model-View-Controller (MVC)
• A pa ern for organizing code o en 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)
Controller
Asks the model for Send request for the story and its a story user comments
View Model Serves requested • Layout of stories story • News stories and on mobile phone or images in a database desktop browser • User comments
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Model-Template-View
In Django: Model-Template-View (similar to MVC pa ern) • 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
View
Handles Asks the model for Send request for Informa on Exchange data data
Template Model Provide Database UI Layout Informa on Communicate with Database
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Your First Django App
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Programming Interface
Terminal / Command Prompt Python IDLE or Favorite editor
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New Project
Project Structure: Whole project in one folder (mysite) • MySite Python package • MySite Python Package • Applica ons (polls) • __init__.py • (Database) • se ngs.py • manage.py • urls.py • Use for interac on with your • wsgi.py project
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First Django Setup
A er a couple commands in terminal...
23 Models
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Models
View
Handles Asks the model for Send request for Informa on Exchange data data
Template Model Provide Database UI Layout Informa on Communicate with Database
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What is a Model
• Python class describing data in your applica on – Subclass of models.Model • Assigns a ributes 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
Import statements
SubClass of models.Model Class Define fields
__unicode__ corresponds to python __str__
Can define more func ons
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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
Define Type of Field Django will • E.g. models.CharField automa cally create Define arguments of field fields in database • E.g. max_length=200 28 GSL South Africa 2015
Important Django Field Types
• BooleanField • FileField – Checkbox • File upload, stores path in database • CharField(max_length) • FloatField – Single-line textbox • Floa ng point numbers • DateField • IntegerField – Javascript calendar Integer textbox • DateTimeField • Posi veIntegerField • – Javascript calendar, me picker Integer textbos for posi ve integers • DecimalField(max_digits, decimal_places) • TextField – Decimal numbers • Mul -line textbox • EmailField – Charfield that validates email address
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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. GSL South Africa 2015
Rela onship Examples: Many-to-One
• A Car has a Manufacturer, but a Manufacturer can have many Cars GSL South Africa 2015
Rela onship Examples: Many-to-Many
• A Pizza can have mul ple Toppings. Each type of Topping can be on mul ple Pizzas GSL South Africa 2015
Rela onship Examples: Many-to-Many • Some mes you need to associate data with the rela onship between a Many-to-Many. GSL South Africa 2015
Rela onship Examples: One-to-One GSL South Africa 2015
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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