Reminders. Full Django products are due next Thursday! CS370, Günay (Emory) Spring / 6

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1 Reminders Full Django products are due next Thursday! CS370, Günay (Emory) Spring / 6

2 Reminders Full Django products are due next Thursday! Let's start by quizzing you. CS370, Günay (Emory) Spring / 6

3 Exit quiz: Persistent Data and Databases in Web Development To maintain user sessions, what pieces of persistent information must be stored on the client and the server side? What is SQL injection attack and how do you protect against it in your webapp? Entry survey: Django Model-View-Controller (or Template) Architecture What's the point of Django's urls.py le? Where's the database in a Django app and how do yo manipulate it?

4 Web Programming in Django Introduction to its Model-View-Controller (or Template) Architecture CS370 SE Practice & Startup, Cengiz Günay (Some slides courtesy of Eugene Agichstein and the Internets) Snowpacolypse ATL 2014 CS370, Günay (Emory) Django MVC intro Spring / 6

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6 high-level Python Web framework that encourages rapid development and clean, pragmatic design. Django was designed to handle two challenges: intensive deadlines stringent requirements of the experienced Web developers who wrote it. It lets you build high-performing, elegant Web applications quickly. Focuses on automating as much as possible 1/24/2013 CS 370, Spring

7 Approach: Model-View-Controller Model: maintain state of application. Typically done with a database View: output to client, usually as HTML code, rendered by a web browser. Controller: interaction with user. handles user input, processes data and communicates with Model to save state. Formalized in /29/2013 CS 370, Spring

8 MVC 1/29/2013 CS 370, Spring

9 1 Visitor's browser asks for a URL. 2 Django matches the request against its urls.py les. 3 If a match is found, Django moves on to the view that's associated with the URL. Views are generally found inside each app in the views.py le. 4 The view generally handles all the database manipulation. It grabs data and passes it on. 5 A template (specied in the view) then displays that data.

10 Site design in Django: review Goal: make common Web-development tasks fast Step 1: Design your model: model.py (M) Automatically create DB, APIs, admin interface Step 2: Design your views: views.py (V) Step 3: Design application logic: urls.py (C) Step 4: Design your templates: Step 5: Enjoy free bells & whistles (caching, syndication, ) 1/29/2013 CS 370, Spring

11 Who cares? Spotify uses Django for some of their web sites. Instagram uses Django for their web application [10] Yandex uses Django for their weather forecast site, OpenID provider, blog hosting service, internal Wiki and internal Mail Archives. Transifex an open source platform for localization. Bucketlist uses Django to let users store life goals. The Public Broadcasting Service The Berkeley Graduate School of Journalism Universal Subtitles uses Django for its free and open source collaborative subtitling site. FreeNAS uses Django for its web interface in its 8.0 major release. PBS's Merlin, a platform for managing member stations' video metadata Google internal stuff (details unknown).. 1/24/2013 CS 370, Spring

12 Example Django Project Tutorial: 1/29/2013 CS 370, Spring

13 Django Models A model is the single, definitive source of data about your data. Each model is a Python class that subclasses django.db.models.model. Each attribute of the model represents a database field. Django gives you an automatically-generated database-access API 1/29/2013 CS 370, Spring

14 Example: Person (first_name, last_name) Define Person: from django.db import models class Person(models.Model): first_name = models.charfield(max_length=30) last_name = models.charfield(max_length=30) What happens automatically CREATE TABLE myapp_person ( "id" serial NOT NULL PRIMARY KEY, "first_name" varchar(30) NOT NULL, "last_name" varchar(30) NOT NULL ); 1/29/2013 CS 370, Spring

15 Example: Person (first_name, last_name): 2 Each field should be an instance of the Field class The database column type (e.g. INTEGER, VARCHAR) The widget to use in Django's admin interface, if you care to use it (e.g. <input type="text">, <select>). The minimal validation requirements, used in Django's automatically-generated forms. Field reference: More details: 1/29/2013 CS 370, Spring

16 Django Models 1/29/2013 CS 370, Spring

17 Recap: Django project pieces django-admin.py startproject blog blog/ init.py: A file required for Python to treat the mysite directory as a package manage.py: A command-line utility that lets you interact with this project. Try: python manage.py help settings.py: Settings/configuration for this project. urls.py: The URLs for this project ( table of contents ) 1/29/2013 CS 370, Spring

18 Django Project vs. App 1/29/2013 CS 370, Spring

19 Django architecture encourages this 1/29/2013 CS 370, Spring

20 Example: 1/29/2013 CS 370, Spring

21 URL dispatcher A clean, elegant URL scheme is an important detail in a high-quality Web application. Django lets you design URLs however you want There s no.php or.cgi required Cool URIs don't change: 1/29/2013 CS 370, Spring

22 How Django processes a request 1. Determine the root URLconf module to use. Ordinarily, this is the value of the ROOT_URLCONF setting, can be changed. 2. Load URLconf and looks for variable urlpatterns. This should be a Python list, in the format returned by the function django.conf.urls.patterns(). 3. Iterate through each URL pattern, in order, and stop at the first one that matches the requested URL. (REGEX) 4. If one of the regexes matches, import and call the given view, which is a Python function. The view gets passed an HttpRequest as its first argument and any values captured in the regex as remaining arguments. 5. If no regex matches, or if an exception is raised during any point in this process, invoke an appropriate error-handling view. 1/29/2013 CS 370, Spring

23 Symbol Matches. (dot) Any single character \d Any single digit [A-Z] [a-z] [A-Za-z] 2-minute REGEX review Any character between A and Z (uppercase) Any character between a and z (lowercase) Any character between a and z (case-insensitive) + One or more of the previous expression (e.g., \d+ matches one or more digits) [^/]+ One or more characters until (and not including) a forward slash? Zero or one of the previous expression (e.g., \d? matches zero or one digits) Zero or more of the previous expression (e.g., \d* matches zero, one or more * than one digit) {1,3} Between one and three (inclusive) of the previous expression (e.g., \d{1,3} matches one, two or three digits) 1/29/2013 CS 370, Spring

24 Python Regexes, cont d To capture a value from the URL, just put parenthesis around it. There's no need to add a leading slash, because every URL has that. For example, it's ^wiki, not ^/wiki. The 'r' is optional but recommended. Named regular-expressions: (?P<name>pattern) (?P<page_name>[^/]+)/$', 1/29/2013 CS 370, Spring

25 Example URLconf from django.conf.urls.defaults import * # urlpatterns = patterns('', ) (r'^wiki/(?p<page_name>[^/]+)/$', 'blog.wiki.views.view_page'), (r'^wiki/(?p<page_name>[^/]+)/edit/$', 'blog.wiki.views.edit_page'), (r'^wiki/(?p<page_name>[^/]+)/save/$', 'blog.wiki.views.save_page'), 1/29/2013 CS 370, Spring

26 Passing Parameters to Views

27 Good Design: Including other URLConfs Your urlpatterns can "include" other URLconf modules. Allows modular sites (good design) urlpatterns = patterns('', (r'^wiki/', include('blog.wiki.urls')) ) Note But: (wiki/urls.py): (r'^(?p<page_name>[^/]+)/$', 'blog.wiki.views.view_page') More details: 1/29/2013 CS 370, Spring

28 Design Pattern: Include URLs There should be one urls.py at the project level, and one urls.py at each app level. The project level urls.py should include each of the urls.py under a prefix.: 1/29/2013 CS 370, Spring

29 Django book: Onwards and upwords Common mistakes/gotchas: To be continued 1/29/2013 CS 370, Spring