django.txt
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Django web framework

 "Full stack" framework, provides:

  URL routing
  Templates
  Testing
  ORM - Object-Relational Mapper for database
  Components for Sessions, Authentication ...

 Flask "microframework" provided all this too, what's the difference?












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Django web framework philosophy - contast to microframeworks

  More prescriptive - makes more decisions for you
   One-stop shopping, not boutiques or DIY
   Their decisions/choices are just DEFAULTS, they are not REQUIRED
  
  It is possible to do a single file Django site - like in Flask (readings)
  
  What must you know?
   URLs, HTML, relational database, regexp, Python, files and directories...
   But NOT HTTP, Apache, WSGI, CGI, environment variables, ...
   Also, supports division of labor
    server/system experts vs. application experts
    database experts vs. HTML/template experts









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Django tools

 Administration and management are centralized
  in a few programs and files

 django-admin.py - run this to get started
 manage.py - run this for many different functions
 settings.py - edit this to configure
 
 python manage.py shell - instead of just python
 python manage.py dbshell - instead of sqlite3 or ...













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Django development cycle - summary

  "What do I do next?" - Django to the rescue!

   django-admin.py startproject <project>
   while in <project> directory:
     (edit settings.py: choose database, INSTALLED_APPS)
     python manage.py syncdb
     python manage.py startapp <app>
     (edit settings.py: add <app>)
     (edit url.py with routes to <app>)
     while in <app> subdirectory:
       (edit <app>/models.py to define database)
       (optionally add and edit urls.py)
       (optionally edit views.py, other .py)
       python manage.py syncdb 
       python manage.py runserver <port>







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Django: create a site (project)

   django-admin.py startproject mysite

 creates your project, a directory with contents

   mysite/
    __init__.py  # the site is a Python package
    manage.py
    settings.py
    urls.py

 (mysite is just a directory name, can be anything)

 A project can contain multiple apps
 







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Django projects: applications

 python manage.py startapp polls
 
creates an app, a subdirectory with contents

 polls/
    __init__.py  # each app is a package - dotted names
    models.py
    tests.py
    views.py
    urls.py      # not created by startup but recommended

(polls is just a name, can be anything)

Edit ../settings.py to add the app, polls







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Django: URL dispatching and views

Recall in Flask the URL decorates the view method

@app.route("/")
def index():
    return render_template('index.html', ....)

Django breaks them up - separates urls.py from views.py
Good idea to separate site urls.py from each app urls.py

In site directory:

urlpatterns = patterns('',
    url(r'^polls/', include('polls.urls')),  # include arg quoted
    url(r'^mailing_list/', include('mailing_list.urls')),
    url(r'^admin/', include(admin.site.urls)), # include arg NOT quoted
    url(r'^databrowse/(.*)', databrowse.site.root),
)

In mailing_list app directory:

urlpatterns = patterns('mailing_list.views',
    url(r'^$', 'index'),
    url(r'^name_list/$', 'name_list'), # mailing_list is name of app
    url(r'^phone_numbers/$', 'phone_numbers'),
    url(r'^query/$', 'query'),
    # more to come?
)

















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Relational database

 Data is represented in a collection of tables with columns
  related by keys - columns of same data appears in multiple tables
 SQL language for defining tables and making queries
 Lots of systems: sqlite, MySQL, PostgreSQL, Oracle, ... 

create table mailing_list (
        email           varchar(100) not null primary key,
        name            varchar(100)
);

create table phone_numbers (
        email           varchar(100) not null references mailing_list(email),
        number_type     varchar(15) check (number_type in ('work','home','cell','beeper')),
        phone_number    varchar(20) not null
);

sqlite> select * from phone_numbers;
ogrady@fastbuck.com|work|(800) 555-1212
ogrady@fastbuck.com|home|(617) 495-6000
philg@mit.edu|work|(617) 253-8574


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Django models

 ORM "object-relational mapper"
 Define tables and make queries in Python
 Underneath it's still SQL and sqlite or MySQL or ...
 Class for each table
 Attributes of the class are the columns

class MailingList(models.Model):
    email = models.CharField(max_length=100, primary_key=True)
    name = models.CharField(max_length=100)

class PhoneNumbers(models.Model):
    NUMBER_TYPE = ((u'work', u'work'), (u'home', u'home'), ...)
    email = models.ForeignKey(MailingList)
    number_type = models.CharField(max_length=6, choices=NUMBER_TYPE)
    phone_number = models.CharField(max_length=20) 






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Django database support

  .../admin/ provides web GUI for entering data

  .../databrowse/ provides web GUI for browsing data

  You can generate models from already-existing database!  
 
  
   # first point to database in settings.py
     python manage.py inspectdb > models.py 

  You can still bypass models, use SQL-in-Python