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![Aggregation
‣ When you need to summarise a collection
of objects
‣ Leveraging the DB where possible
> q = Book.objects.annotate(num_authors=Count('authors'))
> [b.num_authors for b in q]
[2, 3, 1]
> Store.objects.aggregate(min_price=Min('books__price'),
max_price=Max('books__price'))
{‘min_price’ : 2.99, ‘max_price’ : 29.99}
http://docs.djangoproject.com/en/dev/topics/db/aggregation/](https://image.slidesharecdn.com/0909-wa-django-091002054827-phpapp01/85/Introduction-to-Django-25-320.jpg)
Uploaded byJames Casey
Introduction to Django
The document discusses Django, a Python web framework. It began as an internal project at a newspaper to help journalists meet deadlines. Django encourages rapid development, clean design and is database and platform neutral. It features an object relational mapper, automatic admin interface, elegant URLs and templates. Django uses a model-template-view architecture. It provides tools like manage.py to help with development.
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Introduction to Django
- 1. The web frameworkfor perfectionists with deadlines James Casey 2nd October 2009
- 2. What’s Django? “Django isa high-level Python Web framework that encourages rapid development and clean, pragmatic design.” from http://djangoproject.org/
- 3. Whence Django ? ‣Internal project of newspaper in 2003 ‣ Lawrence Journal-World ‣ Should help journalist meet faster deadlines ‣ Should not stand in the way of journalists ‣ Named after the famous guitarist Django Reinhardt
- 4. Django in thenews ‣ http://mps-expenses.guardian.co.uk/ ‣ MP expense scandal ‣ crowdsourcing the review of 500K documents ‣ 7 days from proof-of-concept to launch http://simonwillison.net/2009/talks/europython-crowdsourcing/
- 5. Django won apulitzer ‣ http://polifact.com/ ‣ Fact checking in 2008 US presidental election ‣ Lead developer was former journalist ‣ It was his first django application http://www.mattwaite.com/posts/2007/aug/22/announcing-politifact/
- 6.
- 7. Principles ‣ DRY (Don’tRepeat Yourself) ‣ Write less code ‣ Make CRUD easy ‣ DB neutral ‣ Oracle, MySQL, PostgreSQL, SQLlite ‣ Deployment platform neutral ‣ mod_python, WSGI, ...
- 8.
- 9. Features ‣ Object-relational mapping(ORM) ‣ Automatic admin interface ‣ Elegant URL design ‣ Template system ‣ Caching ‣ i18n
- 10. Architecture Browser Template URL Views Models Database
- 11. Model-Template-View ‣ Models :What things are ‣ Views : How things are processed ‣ Templates : How things are presented
- 12. Models from django.db importmodels class Author(models.Model): name = models.CharField(max_length=100) age = models.IntegerField() friends = models.ManyToManyField('self', blank=True) class Publisher(models.Model): name = models.CharField(max_length=300) num_awards = models.IntegerField() class Book(models.Model): isbn = models.CharField(max_length=9) name = models.CharField(max_length=300) pages = models.IntegerField() price = models.DecimalField(max_digits=10, decimal_places=2) rating = models.FloatField() authors = models.ManyToManyField(Author) publisher = models.ForeignKey(Publisher) pubdate = models.DateField()
- 13. Represents the database objects BEGIN; CREATE TABLE `tutorial_author` ( `id` integer AUTO_INCREMENT NOT NULL PRIMARY KEY, `name` varchar(100) NOT NULL, `age` integer NOT NULL ); CREATE TABLE `tutorial_publisher` ( `id` integer AUTO_INCREMENT NOT NULL PRIMARY KEY, `name` varchar(300) NOT NULL, `num_awards` integer NOT NULL ); ... ... COMMIT;
- 14. ORM books = Book.objects.all() books_this_year= Book.objects.filter(pubdate__gt = jan_1st) apress_books = Book.objects.filter(publisher__name = ‘Apress’) ‣ Never write SQL again ‣ Unless you really need to
- 15. Views ‣ Where allthe magic happens ‣ Normally : ‣ Process model instances ‣ Render HTML ‣ Keep your logic in the model !
- 16. import datetime def view_latest_books(request): # Last 5 days date = datetime.datetime.now() - datetime.timedelta(5) books = Book.objects.filter(pubdate__gte = date).order_by('-pubdate') return render_to_response('tutorial/show_books.html', {'books': books})
- 17. Templates ‣ Separate designfrom code ‣ Separate designers from code ‣ Separate design from developers
- 18. “base.html” <html> <head> <title>{% block title %}{% endblock %}</title> </head> <body> {% block content %}{% endblock %} </body> </html>
- 19. “index.html” {% extends "tutorial/base.html"%} {% block title %}Homepage{% endblock %} {% block content %} {% for book in books %} <h4>{{ book.name }}</h4> <p>Publisher: {{ book.publisher }}</p> <p>Date of Publication: {{ book.pubdate|date }}</p> <p>Price ${{ book.price }}</p> <p>Author : {% for a in book.authors.all %}{{ a.name }}{% if not forloop.last %}, {% endif %}{% endfor %}</p> {% endfor %} {% endblock %}
- 20. Security advantages ‣ Noraw SQL from the users ‣ We deal with models and queries ‣ Automatic HTML escaping ‣ No XSS attacks ‣ CSRF protection ‣ No replay of forms by other code
- 21.
- 22. URLs urlpatterns = patterns('apps.tutorial.views', (r'^$', 'index'), (r’^book/<?P<id>d+)/$’, ‘show_book’), (r'^latest/(?P<num_days>d+)/$', 'view_latest_books'), (r'^create/$', 'create'), ) ‣ URLs map to views (via regular expressions)
- 23.
- 24. Views are justpython functions import datetime def view_latest_books(request, num_days): date = datetime.datetime.now() - datetime.timedelta(int(num_days)) books = Book.objects.filter(pubdate__gte = date).order_by('-pubdate') return render_to_response('books/show_books.html', {'books': books})
- 25. Aggregation ‣ When you need to summarise a collection of objects ‣ Leveraging the DB where possible > q = Book.objects.annotate(num_authors=Count('authors')) > [b.num_authors for b in q] [2, 3, 1] > Store.objects.aggregate(min_price=Min('books__price'), max_price=Max('books__price')) {‘min_price’ : 2.99, ‘max_price’ : 29.99} http://docs.djangoproject.com/en/dev/topics/db/aggregation/
- 26. Other features ‣ Forms ‣Generic Views ‣ Makes CRUD simple ‣ User management ‣ i18n
- 27. My first djangoproject
- 28. Projects contain Applications Project my myapp other_app reuseable app ‣ Application : self-contained set of functions ‣ Project : collection of applications, installed into same database ‣ roughly project == a web application - has a settings file
- 29. Getting started ‣ InstallDjango 1.1 > easy_install django ‣ Create a project > django-admin.py startproject new_django_project new_django_project/ __init__.py manage.py settings.py urls.py
- 30. > ./manage.py startapptutorial new_django_project/ __init__.py manage.py settings.py tutorial/ __init__.py models.py tests.py views.py urls.py
- 31. > ./manage.py runserver Validatingmodels... 0 errors found Django version 1.1, using settings 'new_django_project.settings' Development server is running at http://127.0.0.1:8000/ Quit the server with CONTROL-C. ... ‣ Now you write your code ... > ./manage.py syncdb Creating table django_content_type Creating table django_session Creating table django_site Creating table tutorial_author Creating table tutorial_publisher Creating table tutorial_book Creating table tutorial_store Installing index for tutorial.Book model
- 32. automatic admin interface http://localhost:8000/admin/tutorial/
- 33. manage.py ‣ syncdb :create SQL for your models ‣ shell : start up a python shell with your django project loaded ‣ test : run your unit tests ‣ you did write some, didn’t you ? ‣ inspectdb : reverse engineer models for existing DB ‣ loaddata / dumpdata : load/dump your fixtures from a DB
- 34. Tools to makeyou more productive all just an easy_install away
- 35. distutils ‣ ‘standard’ pythonpackaging ‣ ./setup.py sdist : source packages ‣ /.setup.py bdist : binary packages ‣ Nice to integrate with other tools ‣ pip, unittest, ... ‣ ./setup.py bdist_rpm : Can produce rpm
- 36. Virtualenv ‣ Run separatepython environments ‣ With different sets of packages ‣ And even different interpreters ‣ Easily switch between then ‣ virtualenv_wrapper gives nice bash functions for it all http://pypi.python.org/pypi/virtualenv
- 37. ipython ‣ python withCLI hotness ‣ TAB autocomplete ‣ code coloring ‣ nicer pdb integration ‣ ... http://ipython.scipy.org/moin/
- 39. PIP ‣ Better installationmanager ‣ ‘easy_install’ with dependency ordering ‣ Integrated with virtualenv ‣ Allow to ‘freeze’ a set of packages ‣ and re-install to the same level http://pypi.python.org/pypi/pip
- 40.
- 41. django-command-extensions ‣ Extramanage.py commands ‣ shell_plus : a better python shell ‣ runserver_plus : a better debugging server (werkzeug) ‣ show_urls : dump the url map of your site
- 42.
- 43. and of course,unittest ‣ Django supports : ‣ doctest : useful for simple model validation ‣ unittest : you did write some, didn’t you ? ‣ test client : acts a dummy web browser ‣ Test your views ‣ fixture loading : have a set of complex test data ‣ generated from your production database
- 44. reusable apps if it’suseful, it’s probably been done before...
- 45. south ‣ Schema migration ‣ Change models over time ‣ Write upgrade routines ‣ just python functions with access to .objects and .old_objects
- 46. A platform forrapidly developing (social) websites
- 47. code.google.com ‣ just searchfor django-<WHATEVER> :) ‣ It’s probably there... ‣ If it’s not there, write it and put it there
- 48.
- 49. Multi-DB ‣ Allows yourmodels to be in multiple DBs ‣ Different applications in different DBs ‣ ‘sharding’ of objects across DBs ‣ using slaves for read-only operations
- 50. Other ‣ Admin UIenhancements ‣ autocompletion ‣ better inline handling ‣ Non-relational database support ‣ CouchDB, MongoDB, tokyo Tyrant, Google Bigtable, SimpleDB
- 51.
- 52. ‣ http://docs.djangoproject.com/ ‣ Djangocommunity RSS feed ‣ http://www.djangoproject.com/community/ ‣ Mailing lists ‣ django-dev to understand how the developers think ‣ django-users to ask for help ‣ DjangoCon presentations ‣ http://www.djangocon.org/
- 53.
- 54.
- 55.
- 56. Credits ‣ XKCD forcartoons ‣ Amazon.com for book pictures ‣ Initial inspiration for slides and examples from Joaquim Rocha, Abe Estrada ‣ http://www.slideshare.net/j_rocha/django-intro ‣ http://www.slideshare.net/AbeEstrada/django-web-framework-presentation-822177 ‣ http://www.djangoproject.com/