Let’s learn by example.
Throughout this tutorial, we’ll walk you through the creation of a basic poll application.
It’ll consist of two parts:
We’ll assume you have Django installed already. You can tell Django is installed and which version by running the following command:
python -c "import django; print(django.get_version())"
If Django is installed, you should see the version of your installation. If it isn’t, you’ll get an error telling “No module named django”.
This tutorial is written for Django 1.6 and Python 2.x. If the Django version doesn’t match, you can refer to the tutorial for your version of Django by using the version switcher at the bottom right corner of this page, or update Django to the newest version. If you are using Python 3.x, be aware that your code may need to differ from what is in the tutorial and you should continue using the tutorial only if you know what you are doing with Python 3.x.
See How to install Django for advice on how to remove older versions of Django and install a newer one.
Where to get help:
If you’re having trouble going through this tutorial, please post a message to django-users or drop by #django on irc.freenode.net to chat with other Django users who might be able to help.
If this is your first time using Django, you’ll have to take care of some initial setup. Namely, you’ll need to auto-generate some code that establishes a Django project – a collection of settings for an instance of Django, including database configuration, Django-specific options and application-specific settings.
From the command line, cd
into a directory where you’d like to store your
code, then run the following command:
django-admin.py startproject mysite
This will create a mysite
directory in your current directory. If it didn’t
work, see Problems running django-admin.py.
Note
You’ll need to avoid naming projects after built-in Python or Django
components. In particular, this means you should avoid using names like
django
(which will conflict with Django itself) or test
(which
conflicts with a built-in Python package).
Where should this code live?
If your background is in plain old PHP (with no use of modern frameworks),
you’re probably used to putting code under the Web server’s document root
(in a place such as /var/www
). With Django, you don’t do that. It’s
not a good idea to put any of this Python code within your Web server’s
document root, because it risks the possibility that people may be able
to view your code over the Web. That’s not good for security.
Put your code in some directory outside of the document root, such as
/home/mycode
.
Let’s look at what startproject
created:
mysite/
manage.py
mysite/
__init__.py
settings.py
urls.py
wsgi.py
Doesn’t match what you see?
The default project layout recently changed. If you’re seeing a “flat”
layout (with no inner mysite/
directory), you’re probably using
a version of Django that doesn’t match this tutorial version. You’ll
want to either switch to the older tutorial or the newer Django version.
These files are:
mysite/
root directory is just a container for your
project. Its name doesn’t matter to Django; you can rename it to anything
you like.manage.py
: A command-line utility that lets you interact with this
Django project in various ways. You can read all the details about
manage.py
in django-admin.py and manage.py.mysite/
directory is the actual Python package for your
project. Its name is the Python package name you’ll need to use to import
anything inside it (e.g. mysite.urls
).mysite/__init__.py
: An empty file that tells Python that this
directory should be considered a Python package. (Read more about
packages in the official Python docs if you’re a Python beginner.)mysite/settings.py
: Settings/configuration for this Django
project. Django settings will tell you all about how settings
work.mysite/urls.py
: The URL declarations for this Django project; a
“table of contents” of your Django-powered site. You can read more about
URLs in URL dispatcher.mysite/wsgi.py
: An entry-point for WSGI-compatible web servers to
serve your project. See How to deploy with WSGI for more details.Let’s verify this worked. Change into the outer mysite
directory, if
you haven’t already, and run the command python manage.py runserver
. You’ll
see the following output on the command line:
Validating models... 0 errors found October 03, 2017 - 15:50:53 Django version 1.6, using settings 'mysite.settings' Starting development server at http://127.0.0.1:8000/ Quit the server with CONTROL-C.
You’ve started the Django development server, a lightweight Web server written purely in Python. We’ve included this with Django so you can develop things rapidly, without having to deal with configuring a production server – such as Apache – until you’re ready for production.
Now’s a good time to note: Don’t use this server in anything resembling a production environment. It’s intended only for use while developing. (We’re in the business of making Web frameworks, not Web servers.)
Now that the server’s running, visit http://127.0.0.1:8000/ with your Web browser. You’ll see a “Welcome to Django” page, in pleasant, light-blue pastel. It worked!
Changing the port
By default, the runserver
command starts the development server
on the internal IP at port 8000.
If you want to change the server’s port, pass it as a command-line argument. For instance, this command starts the server on port 8080:
$ python manage.py runserver 8080
If you want to change the server’s IP, pass it along with the port. So to listen on all public IPs (useful if you want to show off your work on other computers), use:
$ python manage.py runserver 0.0.0.0:8000
Full docs for the development server can be found in the
runserver
reference.
Automatic reloading of runserver
The development server automatically reloads Python code for each request as needed. You don’t need to restart the server for code changes to take effect. However, some actions like adding files or compiling translation files don’t trigger a restart, so you’ll have to restart the server in these cases.
Now, edit mysite/settings.py
. It’s a normal Python module with
module-level variables representing Django settings.
By default, the configuration uses SQLite. If you’re new to databases, or you’re just interested in trying Django, this is the easiest choice. SQLite is included in Python, so you won’t need to install anything else to support your database.
If you wish to use another database, install the appropriate database
bindings, and change the following keys in the
DATABASES
'default'
item to match your database connection
settings:
ENGINE
– Either
'django.db.backends.sqlite3'
,
'django.db.backends.postgresql_psycopg2'
,
'django.db.backends.mysql'
, or
'django.db.backends.oracle'
. Other backends are also available
.NAME
– The name of your database. If you’re using SQLite, the
database will be a file on your computer; in that case, NAME
should be the full absolute path, including filename, of that file. The
default value, os.path.join(BASE_DIR, 'db.sqlite3')
, will store the file
in your project directory.If you are not using SQLite as your database, additional settings such as USER
, PASSWORD
, HOST
must be added.
For more details, see the reference documentation for DATABASES
.
Note
If you’re using PostgreSQL or MySQL, make sure you’ve created a database by
this point. Do that with “CREATE DATABASE database_name;
” within your
database’s interactive prompt.
If you’re using SQLite, you don’t need to create anything beforehand - the database file will be created automatically when it is needed.
While you’re editing mysite/settings.py
, set TIME_ZONE
to
your time zone.
Also, note the INSTALLED_APPS
setting at the top of the file. That
holds the names of all Django applications that are activated in this Django
instance. Apps can be used in multiple projects, and you can package and
distribute them for use by others in their projects.
By default, INSTALLED_APPS
contains the following apps, all of which
come with Django:
django.contrib.admin
– The admin site. You’ll use it in part 2
of this tutorial.django.contrib.auth
– An authentication system.django.contrib.contenttypes
– A framework for content types.django.contrib.sessions
– A session framework.django.contrib.messages
– A messaging framework.django.contrib.staticfiles
– A framework for managing
static files.These applications are included by default as a convenience for the common case.
Some of these applications makes use of at least one database table, though, so we need to create the tables in the database before we can use them. To do that, run the following command:
$ python manage.py syncdb
The syncdb
command looks at the INSTALLED_APPS
setting
and creates any necessary database tables according to the database settings
in your mysite/settings.py
file. You’ll see a message for each
database table it creates, and you’ll get a prompt asking you if you’d like to
create a superuser account for the authentication system. Go ahead and do
that.
If you’re interested, run the command-line client for your database and type
\dt
(PostgreSQL), SHOW TABLES;
(MySQL), or .schema
(SQLite) to
display the tables Django created.
For the minimalists
Like we said above, the default applications are included for the common
case, but not everybody needs them. If you don’t need any or all of them,
feel free to comment-out or delete the appropriate line(s) from
INSTALLED_APPS
before running syncdb
. The
syncdb
command will only create tables for apps in
INSTALLED_APPS
.
Now that your environment – a “project” – is set up, you’re set to start doing work.
Each application you write in Django consists of a Python package that follows a certain convention. Django comes with a utility that automatically generates the basic directory structure of an app, so you can focus on writing code rather than creating directories.
Projects vs. apps
What’s the difference between a project and an app? An app is a Web application that does something – e.g., a Weblog system, a database of public records or a simple poll app. A project is a collection of configuration and apps for a particular Web site. A project can contain multiple apps. An app can be in multiple projects.
Your apps can live anywhere on your Python path. In this tutorial, we’ll
create our poll app right next to your manage.py
file so that it can be
imported as its own top-level module, rather than a submodule of mysite
.
To create your app, make sure you’re in the same directory as manage.py
and type this command:
$ python manage.py startapp polls
That’ll create a directory polls
, which is laid out like this:
polls/
__init__.py
admin.py
models.py
tests.py
views.py
This directory structure will house the poll application.
The first step in writing a database Web app in Django is to define your models – essentially, your database layout, with additional metadata.
Philosophy
A model is the single, definitive source of data about your data. It contains the essential fields and behaviors of the data you’re storing. Django follows the DRY Principle. The goal is to define your data model in one place and automatically derive things from it.
In our simple poll app, we’ll create two models: Poll
and Choice
.
A Poll
has a question and a publication date. A Choice
has two fields:
the text of the choice and a vote tally. Each Choice
is associated with a
Poll
.
These concepts are represented by simple Python classes. Edit the
polls/models.py
file so it looks like this:
from django.db import models
class Poll(models.Model):
question = models.CharField(max_length=200)
pub_date = models.DateTimeField('date published')
class Choice(models.Model):
poll = models.ForeignKey(Poll)
choice_text = models.CharField(max_length=200)
votes = models.IntegerField(default=0)
The code is straightforward. Each model is represented by a class that
subclasses django.db.models.Model
. Each model has a number of class
variables, each of which represents a database field in the model.
Each field is represented by an instance of a Field
class – e.g., CharField
for character fields and
DateTimeField
for datetimes. This tells Django what
type of data each field holds.
The name of each Field
instance (e.g. question
or
pub_date
) is the field’s name, in machine-friendly format. You’ll use this
value in your Python code, and your database will use it as the column name.
You can use an optional first positional argument to a
Field
to designate a human-readable name. That’s used
in a couple of introspective parts of Django, and it doubles as documentation.
If this field isn’t provided, Django will use the machine-readable name. In this
example, we’ve only defined a human-readable name for Poll.pub_date
. For all
other fields in this model, the field’s machine-readable name will suffice as
its human-readable name.
Some Field
classes have required arguments.
CharField
, for example, requires that you give it a
max_length
. That’s used not only in the
database schema, but in validation, as we’ll soon see.
A Field
can also have various optional arguments; in
this case, we’ve set the default
value of
votes
to 0.
Finally, note a relationship is defined, using
ForeignKey
. That tells Django each Choice
is related
to a single Poll
. Django supports all the common database relationships:
many-to-ones, many-to-manys and one-to-ones.
That small bit of model code gives Django a lot of information. With it, Django is able to:
CREATE TABLE
statements) for this app.Poll
and Choice
objects.But first we need to tell our project that the polls
app is installed.
Philosophy
Django apps are “pluggable”: You can use an app in multiple projects, and you can distribute apps, because they don’t have to be tied to a given Django installation.
Edit the mysite/settings.py
file again, and change the
INSTALLED_APPS
setting to include the string 'polls'
. So it’ll
look like this:
INSTALLED_APPS = (
'django.contrib.admin',
'django.contrib.auth',
'django.contrib.contenttypes',
'django.contrib.sessions',
'django.contrib.messages',
'django.contrib.staticfiles',
'polls',
)
Now Django knows to include the polls
app. Let’s run another command:
$ python manage.py sql polls
You should see something similar to the following (the CREATE TABLE
SQL
statements for the polls app):
BEGIN;
CREATE TABLE "polls_poll" (
"id" integer NOT NULL PRIMARY KEY,
"question" varchar(200) NOT NULL,
"pub_date" datetime NOT NULL
);
CREATE TABLE "polls_choice" (
"id" integer NOT NULL PRIMARY KEY,
"poll_id" integer NOT NULL REFERENCES "polls_poll" ("id"),
"choice_text" varchar(200) NOT NULL,
"votes" integer NOT NULL
);
COMMIT;
Note the following:
polls
) and the lowercase name of the model – poll
and
choice
. (You can override this behavior.)"_id"
to the foreign key field name.
(Yes, you can override this, as well.)REFERENCES
statement.auto_increment
(MySQL), serial
(PostgreSQL), or
integer primary key
(SQLite) are handled for you automatically. Same
goes for quoting of field names – e.g., using double quotes or single
quotes.sql
command doesn’t actually run the SQL in your database -
it just prints it to the screen so that you can see what SQL Django thinks
is required. If you wanted to, you could copy and paste this SQL into your
database prompt. However, as we will see shortly, Django provides an
easier way of committing the SQL to the database.If you’re interested, also run the following commands:
python manage.py validate
– Checks for any errors
in the construction of your models.python manage.py sqlcustom polls
– Outputs any
custom SQL statements (such as table modifications or
constraints) that are defined for the application.python manage.py sqlclear polls
– Outputs the
necessary DROP TABLE
statements for this app, according to which
tables already exist in your database (if any).python manage.py sqlindexes polls
– Outputs the
CREATE INDEX
statements for this app.python manage.py sqlall polls
– A combination of all
the SQL from the sql
, sqlcustom
, and
sqlindexes
commands.Looking at the output of those commands can help you understand what’s actually happening under the hood.
Now, run syncdb
again to create those model tables in your database:
$ python manage.py syncdb
The syncdb
command runs the SQL from sqlall
on your
database for all apps in INSTALLED_APPS
that don’t already exist in
your database. This creates all the tables, initial data and indexes for any
apps you’ve added to your project since the last time you ran syncdb.
syncdb
can be called as often as you like, and it will only ever
create the tables that don’t exist.
Read the django-admin.py documentation for full
information on what the manage.py
utility can do.
Now, let’s hop into the interactive Python shell and play around with the free API Django gives you. To invoke the Python shell, use this command:
$ python manage.py shell
We’re using this instead of simply typing “python”, because manage.py
sets the DJANGO_SETTINGS_MODULE
environment variable, which gives Django
the Python import path to your mysite/settings.py
file.
Bypassing manage.py
If you’d rather not use manage.py
, no problem. Just set the
DJANGO_SETTINGS_MODULE
environment variable to mysite.settings
and
run python
from the same directory manage.py
is in (or ensure
that directory is on the Python path, so that import mysite
works).
For more information on all of this, see the django-admin.py documentation.
Once you’re in the shell, explore the database API:
>>> from polls.models import Poll, Choice # Import the model classes we just wrote.
# No polls are in the system yet.
>>> Poll.objects.all()
[]
# Create a new Poll.
# Support for time zones is enabled in the default settings file, so
# Django expects a datetime with tzinfo for pub_date. Use timezone.now()
# instead of datetime.datetime.now() and it will do the right thing.
>>> from django.utils import timezone
>>> p = Poll(question="What's new?", pub_date=timezone.now())
# Save the object into the database. You have to call save() explicitly.
>>> p.save()
# Now it has an ID. Note that this might say "1L" instead of "1", depending
# on which database you're using. That's no biggie; it just means your
# database backend prefers to return integers as Python long integer
# objects.
>>> p.id
1
# Access database columns via Python attributes.
>>> p.question
"What's new?"
>>> p.pub_date
datetime.datetime(2012, 2, 26, 13, 0, 0, 775217, tzinfo=<UTC>)
# Change values by changing the attributes, then calling save().
>>> p.question = "What's up?"
>>> p.save()
# objects.all() displays all the polls in the database.
>>> Poll.objects.all()
[<Poll: Poll object>]
Wait a minute. <Poll: Poll object>
is, utterly, an unhelpful representation
of this object. Let’s fix that by editing the polls model (in the
polls/models.py
file) and adding a
__unicode__()
method to both Poll
and
Choice
. On Python 3, simply replace __unicode__
by __str__
in the
following example:
from django.db import models
class Poll(models.Model):
# ...
def __unicode__(self): # Python 3: def __str__(self):
return self.question
class Choice(models.Model):
# ...
def __unicode__(self): # Python 3: def __str__(self):
return self.choice_text
It’s important to add __unicode__()
methods (or
__str__()
on Python 3) to your models, not only
for your own sanity when dealing with the interactive prompt, but also because
objects’ representations are used throughout Django’s automatically-generated
admin.
__unicode__ or __str__?
On Python 3, things are simpler, just use
__str__()
and forget about
__unicode__()
.
If you’re familiar with Python 2, you might be in the habit of adding
__str__()
methods to your classes, not
__unicode__()
methods. We use
__unicode__()
here because Django models deal
with Unicode by default. All data stored in your database is converted to
Unicode when it’s returned.
Django models have a default __str__()
method
that calls __unicode__()
and converts the
result to a UTF-8 bytestring. This means that unicode(p)
will return a
Unicode string, and str(p)
will return a normal string, with characters
encoded as UTF-8.
If all of this is gibberish to you, just remember to add
__unicode__()
methods to your models. With any
luck, things should Just Work for you.
Note these are normal Python methods. Let’s add a custom method, just for demonstration:
import datetime
from django.utils import timezone
# ...
class Poll(models.Model):
# ...
def was_published_recently(self):
return self.pub_date >= timezone.now() - datetime.timedelta(days=1)
Note the addition of import datetime
and from django.utils import
timezone
, to reference Python’s standard datetime
module and Django’s
time-zone-related utilities in django.utils.timezone
, respectively. If
you aren’t familiar with time zone handling in Python, you can learn more in
the time zone support docs.
Save these changes and start a new Python interactive shell by running
python manage.py shell
again:
>>> from polls.models import Poll, Choice
# Make sure our __unicode__() addition worked.
>>> Poll.objects.all()
[<Poll: What's up?>]
# Django provides a rich database lookup API that's entirely driven by
# keyword arguments.
>>> Poll.objects.filter(id=1)
[<Poll: What's up?>]
>>> Poll.objects.filter(question__startswith='What')
[<Poll: What's up?>]
# Get the poll that was published this year.
>>> from django.utils import timezone
>>> current_year = timezone.now().year
>>> Poll.objects.get(pub_date__year=current_year)
<Poll: What's up?>
# Request an ID that doesn't exist, this will raise an exception.
>>> Poll.objects.get(id=2)
Traceback (most recent call last):
...
DoesNotExist: Poll matching query does not exist.
# Lookup by a primary key is the most common case, so Django provides a
# shortcut for primary-key exact lookups.
# The following is identical to Poll.objects.get(id=1).
>>> Poll.objects.get(pk=1)
<Poll: What's up?>
# Make sure our custom method worked.
>>> p = Poll.objects.get(pk=1)
>>> p.was_published_recently()
True
# Give the Poll a couple of Choices. The create call constructs a new
# Choice object, does the INSERT statement, adds the choice to the set
# of available choices and returns the new Choice object. Django creates
# a set to hold the "other side" of a ForeignKey relation
# (e.g. a poll's choices) which can be accessed via the API.
>>> p = Poll.objects.get(pk=1)
# Display any choices from the related object set -- none so far.
>>> p.choice_set.all()
[]
# Create three choices.
>>> p.choice_set.create(choice_text='Not much', votes=0)
<Choice: Not much>
>>> p.choice_set.create(choice_text='The sky', votes=0)
<Choice: The sky>
>>> c = p.choice_set.create(choice_text='Just hacking again', votes=0)
# Choice objects have API access to their related Poll objects.
>>> c.poll
<Poll: What's up?>
# And vice versa: Poll objects get access to Choice objects.
>>> p.choice_set.all()
[<Choice: Not much>, <Choice: The sky>, <Choice: Just hacking again>]
>>> p.choice_set.count()
3
# The API automatically follows relationships as far as you need.
# Use double underscores to separate relationships.
# This works as many levels deep as you want; there's no limit.
# Find all Choices for any poll whose pub_date is in this year
# (reusing the 'current_year' variable we created above).
>>> Choice.objects.filter(poll__pub_date__year=current_year)
[<Choice: Not much>, <Choice: The sky>, <Choice: Just hacking again>]
# Let's delete one of the choices. Use delete() for that.
>>> c = p.choice_set.filter(choice_text__startswith='Just hacking')
>>> c.delete()
For more information on model relations, see Accessing related objects. For more on how to use double underscores to perform field lookups via the API, see Field lookups. For full details on the database API, see our Database API reference.
When you’re comfortable with the API, read part 2 of this tutorial to get Django’s automatic admin working.
Oct 03, 2017