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magic-removal: Proofread docs/overview.txt
git-svn-id: http://code.djangoproject.com/svn/django/branches/magic-removal@2787 bcc190cf-cafb-0310-a4f2-bffc1f526a37
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@ -16,34 +16,39 @@ to start a project.
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Design your model
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Design your model
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=================
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=================
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Start by describing your database layout in Python code. Django's data-model API
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Although you can use Django without a database, it comes with an
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offers many rich ways of representing your models -- so far, it's been
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object-relational mapper in which you describe your database layout in Python
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solving two years' worth of database-schema problems. Here's a quick example::
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code.
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class Reporter(meta.Model):
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The data-model syntax offers many rich ways of representing your models -- so
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full_name = meta.CharField(maxlength=70)
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far, it's been solving two years' worth of database-schema problems. Here's a
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quick example::
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def __repr__(self):
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class Reporter(models.Model):
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full_name = models.CharField(maxlength=70)
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def __str__(self):
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return self.full_name
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return self.full_name
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class Article(meta.Model):
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class Article(models.Model):
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pub_date = meta.DateTimeField()
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pub_date = models.DateTimeField()
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headline = meta.CharField(maxlength=200)
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headline = models.CharField(maxlength=200)
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article = meta.TextField()
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article = models.TextField()
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reporter = meta.ForeignKey(Reporter)
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reporter = models.ForeignKey(Reporter)
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def __repr__(self):
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def __str__(self):
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return self.headline
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return self.headline
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Install it
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Install it
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==========
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==========
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Next, run the Django command-line utility. It'll create the database tables for
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Next, run the Django command-line utility to create the database tables
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you automatically, in the database specified in your Django settings. Django
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automatically::
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works best with PostgreSQL, although we've recently added beta MySQL
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support and other database adapters are on the way::
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django-admin.py install news
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manage.py syncdb
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The ``syncdb`` command looks at all your available models and creates tables
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in your database for whichever tables don't already exist.
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Enjoy the free API
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Enjoy the free API
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==================
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==================
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@ -51,16 +56,14 @@ Enjoy the free API
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With that, you've got a free, and rich, Python API to access your data. The API
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With that, you've got a free, and rich, Python API to access your data. The API
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is created on the fly: No code generation necessary::
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is created on the fly: No code generation necessary::
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# Modules are dynamically created within django.models.
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>>> from mysite.models import Reporter, Article
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# Their names are plural versions of the model class names.
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>>> from django.models.news import reporters, articles
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# No reporters are in the system yet.
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# No reporters are in the system yet.
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>>> reporters.get_list()
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>>> Reporter.objects.all()
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[]
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[]
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# Create a new Reporter.
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# Create a new Reporter.
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>>> r = reporters.Reporter(full_name='John Smith')
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>>> r = Reporter(full_name='John Smith')
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# Save the object into the database. You have to call save() explicitly.
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# Save the object into the database. You have to call save() explicitly.
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>>> r.save()
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>>> r.save()
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@ -70,52 +73,48 @@ is created on the fly: No code generation necessary::
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1
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1
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# Now the new reporter is in the database.
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# Now the new reporter is in the database.
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>>> reporters.get_list()
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>>> Reporter.objects.all()
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[John Smith]
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[John Smith]
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# Fields are represented as attributes on the Python object.
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# Fields are represented as attributes on the Python object.
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>>> r.full_name
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>>> r.full_name
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'John Smith'
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'John Smith'
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# Django provides a rich database lookup API that's entirely driven by keyword arguments.
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# Django provides a rich database lookup API.
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>>> reporters.get_object(id__exact=1)
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>>> Reporter.objects.get(id=1)
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John Smith
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John Smith
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>>> reporters.get_object(full_name__startswith='John')
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>>> Reporter.objects.get(full_name__startswith='John')
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John Smith
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John Smith
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>>> reporters.get_object(full_name__contains='mith')
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>>> Reporter.objects.get(full_name__contains='mith')
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John Smith
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John Smith
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>>> reporters.get_object(id__exact=2)
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>>> Reporter.objects.get(id=2)
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Traceback (most recent call last):
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Traceback (most recent call last):
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...
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...
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django.models.news.ReporterDoesNotExist: Reporter does not exist for {'id__exact': 2}
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DoesNotExist: Reporter does not exist for {'id__exact': 2}
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# Lookup by a primary key is the most common case, so Django provides a
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# shortcut for primary-key exact lookups.
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# The following is identical to reporters.get_object(id__exact=1).
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>>> reporters.get_object(pk=1)
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John Smith
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# Create an article.
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# Create an article.
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>>> from datetime import datetime
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>>> from datetime import datetime
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>>> a = articles.Article(pub_date=datetime.now(), headline='Django is cool', article='Yeah.', reporter_id=1)
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>>> a = Article(pub_date=datetime.now(), headline='Django is cool',
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... article='Yeah.', reporter=r)
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>>> a.save()
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>>> a.save()
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# Now the article is in the database.
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# Now the article is in the database.
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>>> articles.get_list()
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>>> Article.objects.all()
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[Django is cool]
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[Django is cool]
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# Article objects get API access to related Reporter objects.
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# Article objects get API access to related Reporter objects.
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>>> r = a.get_reporter()
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>>> r = a.reporter
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>>> r.full_name
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>>> r.full_name
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'John Smith'
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'John Smith'
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# And vice versa: Reporter objects get API access to Article objects.
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# And vice versa: Reporter objects get API access to Article objects.
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>>> r.get_article_list()
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>>> r.article_set.all()
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[Django is cool]
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[Django is cool]
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# The API follows relationships as far as you need.
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# The API follows relationships as far as you need, performing efficient
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# Find all articles by a reporter whose name starts with "John".
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# JOINs for you behind the scenes.
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>>> articles.get_list(reporter__full_name__startswith="John")
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# This finds all articles by a reporter whose name starts with "John".
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>>> Article.objects.filter(reporter__full_name__startswith="John")
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[Django is cool]
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[Django is cool]
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# Change an object by altering its attributes and calling save().
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# Change an object by altering its attributes and calling save().
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@ -128,61 +127,64 @@ is created on the fly: No code generation necessary::
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A dynamic admin interface: It's not just scaffolding -- it's the whole house
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A dynamic admin interface: It's not just scaffolding -- it's the whole house
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============================================================================
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============================================================================
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Once your models are defined, Django can automatically create an administrative
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Once your models are defined, Django can automatically create a professional,
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interface -- a Web site that lets authenticated users add, change and
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production ready administrative interface -- a Web site that lets authenticated
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delete objects. It's as easy as adding an extra ``admin`` attribute to your
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users add, change and delete objects. It's as easy as adding a line of code to
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model classes::
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your model classes::
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class Article(meta.Model):
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class Article(models.Model):
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pub_date = meta.DateTimeField()
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pub_date = models.DateTimeField()
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headline = meta.CharField(maxlength=200)
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headline = models.CharField(maxlength=200)
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article = meta.TextField()
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article = models.TextField()
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reporter = meta.ForeignKey(Reporter)
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reporter = models.ForeignKey(Reporter)
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class Meta:
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class Admin: pass
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admin = meta.Admin()
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The philosophy here is that your site is edited by a staff, or a client, or
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The philosophy here is that your site is edited by a staff, or a client, or
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maybe just you -- and you don't want to have to deal with creating backend
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maybe just you -- and you don't want to have to deal with creating backend
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interfaces just to manage content.
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interfaces just to manage content.
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Our typical workflow at World Online is to create models and get the admin sites
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One typical workflow in creating Django apps is to create models and get the
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up and running as fast as possible, so our staff journalists can start
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admin sites up and running as fast as possible, so your staff (or clients) can
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populating data. Then we develop the way data is presented to the public.
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start populating data. Then, develop the way data is presented to the public.
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Design your URLs
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Design your URLs
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================
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================
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A clean, elegant URL scheme is an important detail in a high-quality Web
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A clean, elegant URL scheme is an important detail in a high-quality Web
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application. Django lets you design URLs however you want, with no framework
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application. Django encourages beautiful URL design and doesn't put any cruft
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limitations.
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in URLs, like ``.php`` or ``.asp``.
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To design URLs for an app, you create a Python module. For the above
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To design URLs for an app, you create a Python module called a URLconf. A table
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Reporter/Article example, here's what that might look like::
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of contents for your app, it contains a simple mapping between URL patterns and
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Python callback functions. URLconfs also serve to decouple URLs from Python
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code.
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Here's what a URLconf might look like for the above ``Reporter``/``Article``
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example above::
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from django.conf.urls.defaults import *
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from django.conf.urls.defaults import *
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urlpatterns = patterns('',
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urlpatterns = patterns('',
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(r'^/articles/(?P<year>\d{4})/$', 'myproject.news.views.year_archive'),
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(r'^/articles/(\d{4})/$', 'mysite.views.year_archive'),
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(r'^/articles/(?P<year>\d{4})/(?P<month>\d{2})/$', 'myproject.news.views.month_archive'),
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(r'^/articles/(\d{4})/(\d{2})/$', 'mysite.views.month_archive'),
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(r'^/articles/(?P<year>\d{4})/(?P<month>\d{2})/(?P<article_id>\d+)/$', 'myproject.news.views.article_detail'),
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(r'^/articles/(\d{4})/(\d{2})/(\d+)/$', 'mysite.views.article_detail'),
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)
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)
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The code above maps URLs, as regular expressions, to the location of Python
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The code above maps URLs, as simple regular expressions, to the location of
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callback functions (views). The regular expressions use parenthesis to "capture"
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Python callback functions ("views"). The regular expressions use parenthesis to
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values from the URLs. When a user requests a page, Django runs through each
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"capture" values from the URLs. When a user requests a page, Django runs
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regular expression, in order, and stops at the first one that matches the
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through each pattern, in order, and stops at the first one that matches the
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requested URL. (If none of them matches, Django calls a special 404 view.) This
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requested URL. (If none of them matches, Django calls a special-case 404 view.)
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is blazingly fast, because the regular expressions are compiled at load time.
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This is blazingly fast, because the regular expressions are compiled at load
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time.
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Once one of the regexes matches, Django imports and calls the given view, which
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Once one of the regexes matches, Django imports and calls the given view, which
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is a simple Python function. Each view gets passed a request object --
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is a simple Python function. Each view gets passed a request object --
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which contains request metadata and lets you access GET and POST data as simple
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which contains request metadata -- and the values captured in the regex.
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dictionaries -- and the values captured in the regex, via keyword
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arguments.
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For example, if a user requested the URL "/articles/2005/05/39323/", Django
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For example, if a user requested the URL "/articles/2005/05/39323/", Django
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would call the function ``myproject.news.views.article_detail(request,
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would call the function ``myproject.news.views.article_detail(request,
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year='2005', month='05', article_id='39323')``.
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'2005', '05', '39323')``.
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Write your views
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Write your views
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================
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================
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@ -193,29 +195,29 @@ raising an exception such as ``Http404``. The rest is up to you.
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Generally, a view retrieves data according to the parameters, loads a template
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Generally, a view retrieves data according to the parameters, loads a template
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and renders the template with the retrieved data. Here's an example view for
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and renders the template with the retrieved data. Here's an example view for
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article_detail from above::
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``year_archive`` from above::
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def article_detail(request, year, month, article_id):
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def year_archive(request, year):
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# Use the Django API to find an object matching the URL criteria.
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a_list = Article.objects.filter(pub_date__year=year)
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a = get_object_or_404(articles, pub_date__year=year, pub_date__month=month, pk=article_id)
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return render_to_response('news/year_archive.html', {'article_list': a_list})
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return render_to_response('news/article_detail.html', {'article': a})
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This example uses Django's template system, which has several key features.
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This example uses Django's template system, which has several powerful
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features but strives to stay simple enough for non-programmers to use.
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Design your templates
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Design your templates
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=====================
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=====================
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The code above loads the ``news/article_detail`` template.
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The code above loads the ``news/year_archive.html`` template.
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Django has a template search path, which allows you to minimize redundancy among
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Django has a template search path, which allows you to minimize redundancy among
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templates. In your Django settings, you specify a list of directories to check
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templates. In your Django settings, you specify a list of directories to check
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for templates. If a template doesn't exist in the first directory, it checks the
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for templates. If a template doesn't exist in the first directory, it checks the
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second, and so on.
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second, and so on.
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Let's say the ``news/article_detail`` template was found. Here's what that might
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Let's say the ``news/article_detail.html`` template was found. Here's what that
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look like::
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might look like::
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{% extends "base" %}
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{% extends "base.html" %}
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{% block title %}{{ article.headline }}{% endblock %}
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{% block title %}{{ article.headline }}{% endblock %}
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{{ article.article }}
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{{ article.article }}
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{% endblock %}
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{% endblock %}
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Variables are surrounded by double-curly braces. ``{{ article.headline }}``
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It should look straightforward. Variables are surrounded by double-curly braces.
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means "Output the value of the article's headline attribute." But dots aren't
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``{{ article.headline }}`` means "Output the value of the article's headline
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used only for attribute lookup: They also can do dictionary-key lookup, index
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attribute." But dots aren't used only for attribute lookup: They also can do
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lookup and function calls (as is the case with ``article.get_reporter``).
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dictionary-key lookup, index lookup and function calls (as is the case with
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``article.get_reporter``).
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Note ``{{ article.pub_date|date:"F j, Y" }}`` uses a Unix-style "pipe" (the "|"
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Note ``{{ article.pub_date|date:"F j, Y" }}`` uses a Unix-style "pipe" (the "|"
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character). This is called a template filter, and it's a way to filter the value
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character). This is called a template filter, and it's a way to filter the value
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filters. You can write custom template tags, which run custom Python code behind
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filters. You can write custom template tags, which run custom Python code behind
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the scenes.
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the scenes.
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Finally, Django uses the concept of template inheritance: That's what the ``{%
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Finally, Django uses the concept of "template inheritance": That's what the
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extends "base" %}`` does. It means "First load the template called 'base', which
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``{% extends "base.html" %}`` does. It means "First load the template called
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has defined a bunch of blocks, and fill the blocks with the following blocks."
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'base', which has defined a bunch of blocks, and fill the blocks with the
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In short, that lets you dramatically cut down on redundancy in templates: Each
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following blocks." In short, that lets you dramatically cut down on redundancy
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template has to define only what's unique to that template.
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in templates: Each template has to define only what's unique to that template.
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Here's what the "base" template might look like::
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Here's what the "base.html" template might look like::
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<html>
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<html>
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<head>
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<head>
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and provides "holes" for child templates to fill. This makes a site redesign as
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and provides "holes" for child templates to fill. This makes a site redesign as
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easy as changing a single file -- the base template.
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easy as changing a single file -- the base template.
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It also lets you create multiple versions of a site, with different base
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templates, while reusing child templates. Django's creators have used this
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technique to create strikingly different cell-phone editions of sites -- simply
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by creating a new base template.
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Note that you don't have to use Django's template system if you prefer another
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Note that you don't have to use Django's template system if you prefer another
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system. While Django's template system is particularly well-integrated with
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system. While Django's template system is particularly well-integrated with
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Django's model layer, nothing forces you to use it. For that matter, you don't
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Django's model layer, nothing forces you to use it. For that matter, you don't
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have to use Django's API, either. You can use another database abstraction
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have to use Django's database API, either. You can use another database
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layer, you can read XML files, you can read files off disk, or anything you
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abstraction layer, you can read XML files, you can read files off disk, or
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want. Each piece of Django -- models, views, templates -- is decoupled
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anything you want. Each piece of Django -- models, views, templates -- is
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from the next.
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decoupled from the next.
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This is just the surface
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This is just the surface
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========================
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========================
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