Writing your first Django app, part 1¶
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:
- A public site that lets people view polls and vote in them.
- An admin site that lets you add, change and delete polls.
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 1.7 and Python 3.2 or later. 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 still using Python 2.7, you will need to adjust the code samples slightly, as described in comments.
See How to install Django for advice on how to remove older versions of Django and install a newer one.
Where to get help:
Creating a project¶
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.
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
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
Let’s look at what
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:
- The outer
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.pyin django-admin.py and manage.py.
- The inner
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/__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.
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. When starting your first real project, however, you may want to use a more robust database like PostgreSQL, to avoid database-switching headaches down the road.
'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,
NAMEshould 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’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
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.
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 make 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 migrate
migrate command looks at the
and creates any necessary database tables according to the database settings
mysite/settings.py file and the database migrations shipped
with the app (we’ll cover those later). You’ll see a message for each
migration it applies. If you’re interested, run the command-line client for your
database and type
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
migrate command will only run migrations for apps in
The development server¶
Let’s verify your Django project works. Change into the outer
mysite directory, if
you haven’t already, and run the following commands:
$ python manage.py runserver
You’ll see the following output on the command line:
Performing system checks... 0 errors found December 13, 2016 - 15:50:53 Django version 1.7, 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
Automatic reloading of
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 don’t trigger a restart, so you’ll have to restart the server in these cases.
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
To create your app, make sure you’re in the same directory as
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 migrations/ __init__.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.
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.
This includes the migrations - unlike in Ruby On Rails, for example, migrations are entirely derived from your models file, and are essentially just a history that Django can roll through to update your database schema to match your current models.
In our simple poll app, we’ll create two models:
Question 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
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 Question(models.Model): question_text = models.CharField(max_length=200) pub_date = models.DateTimeField('date published') class Choice(models.Model): question = models.ForeignKey(Question) choice_text = models.CharField(max_length=200) votes = models.IntegerField(default=0)
The code is straightforward. Each model is represented by a class that
django.db.models.Model. Each model has a number of class
variables, each of which represents a database field in the model.
The name of each
Field instance (e.g.
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
Question.pub_date. For all
other fields in this model, the field’s machine-readable name will suffice as
its human-readable name.
Finally, note a relationship is defined, using
ForeignKey. That tells Django each
Choice is related
to a single
Question. Django supports all the common database relationships:
many-to-one, many-to-many and one-to-one.
That small bit of model code gives Django a lot of information. With it, Django is able to:
- Create a database schema (
CREATE TABLEstatements) for this app.
- Create a Python database-access API for accessing
But first we need to tell our project that the
polls app is installed.
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.
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 makemigrations polls
You should see something similar to the following:
Migrations for 'polls': 0001_initial.py: - Create model Question - Create model Choice - Add field question to choice
makemigrations, you’re telling Django that you’ve made
some changes to your models (in this case, you’ve made new ones) and that
you’d like the changes to be stored as a migration.
Migrations are how Django stores changes to your models (and thus your
database schema) - they’re just files on disk. You can read the migration
for your new model if you like; it’s the file
polls/migrations/0001_initial.py. Don’t worry, you’re not expected to read
them every time Django makes one, but they’re designed to be human-editable
in case you want to manually tweak how Django changes things.
There’s a command that will run the migrations for you and manage your database
schema automatically - that’s called
migrate, and we’ll come to it in a
moment - but first, let’s see what SQL that migration would run. The
sqlmigrate command takes migration names and returns their SQL:
$ python manage.py sqlmigrate polls 0001
You should see something similar to the following (we’ve reformatted it for readability):
BEGIN; CREATE TABLE "polls_choice" ( "id" serial NOT NULL PRIMARY KEY, "choice_text" varchar(200) NOT NULL, "votes" integer NOT NULL ); CREATE TABLE "polls_question" ( "id" serial NOT NULL PRIMARY KEY, "question_text" varchar(200) NOT NULL, "pub_date" timestamp with time zone NOT NULL ); ALTER TABLE "polls_choice" ADD COLUMN "question_id" integer NOT NULL; ALTER TABLE "polls_choice" ALTER COLUMN "question_id" DROP DEFAULT; CREATE INDEX "polls_choice_7aa0f6ee" ON "polls_choice" ("question_id"); ALTER TABLE "polls_choice" ADD CONSTRAINT "polls_choice_question_id_246c99a640fbbd72_fk_polls_question_id" FOREIGN KEY ("question_id") REFERENCES "polls_question" ("id") DEFERRABLE INITIALLY DEFERRED; COMMIT;
Note the following:
- The exact output will vary depending on the database you are using. The example above is generated for PostgreSQL.
- Table names are automatically generated by combining the name of the app
polls) and the lowercase name of the model –
choice. (You can override this behavior.)
- Primary keys (IDs) are added automatically. (You can override this, too.)
- By convention, Django appends
"_id"to the foreign key field name. (Yes, you can override this, as well.)
- The foreign key relationship is made explicit by a
FOREIGN KEYconstraint. Don’t worry about the
DEFERRABLEparts; that’s just telling PostgreSQL to not enforce the foreign key until the end of the transaction.
- It’s tailored to the database you’re using, so database-specific field types
integer primary key autoincrement(SQLite) are handled for you automatically. Same goes for quoting of field names – e.g., using double quotes or single quotes.
sqlmigratecommand doesn’t actually run the migration on your database - it just prints it to the screen so that you can see what SQL Django thinks is required. It’s useful for checking what Django is going to do or if you have database administrators who require SQL scripts for changes.
If you’re interested, you can also run
python manage.py check; this checks for any problems in
your project without making migrations or touching the database.
migrate again to create those model tables in your database:
$ python manage.py migrate Operations to perform: Apply all migrations: admin, contenttypes, polls, auth, sessions Running migrations: Applying <migration name>... OK
migrate command takes all the migrations that haven’t been
applied (Django tracks which ones are applied using a special table in your
django_migrations) and runs them against your database -
essentially, synchronizing the changes you made to your models with the schema
in the database.
Migrations are very powerful and let you change your models over time, as you develop your project, without the need to delete your database or tables and make new ones - it specializes in upgrading your database live, without losing data. We’ll cover them in more depth in a later part of the tutorial, but for now, remember the three-step guide to making model changes:
- Change your models (in
python manage.py makemigrationsto create migrations for those changes
python manage.py migrateto apply those changes to the database.
The reason there’s separate commands to make and apply migrations is because you’ll commit migrations to your version control system and ship them with your app; they not only make your development easier, they’re also useable by other developers and in production.
Read the django-admin.py documentation for full
information on what the
manage.py utility can do.
Playing with the API¶
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
DJANGO_SETTINGS_MODULE environment variable, which gives Django
the Python import path to your
If you’d rather not use
manage.py, no problem. Just set the
DJANGO_SETTINGS_MODULE environment variable to
mysite.settings, start a plain Python shell, and set up Django:
>>> import django >>> django.setup()
If this raises an
AttributeError, 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.
You must run
python from the same directory
manage.py is in,
or ensure that directory is on the Python path, so that
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 Question, Choice # Import the model classes we just wrote. # No questions are in the system yet. >>> Question.objects.all()  # Create a new Question. # 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 >>> q = Question(question_text="What's new?", pub_date=timezone.now()) # Save the object into the database. You have to call save() explicitly. >>> q.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. >>> q.id 1 # Access model field values via Python attributes. >>> q.question_text "What's new?" >>> q.pub_date datetime.datetime(2012, 2, 26, 13, 0, 0, 775217, tzinfo=<UTC>) # Change values by changing the attributes, then calling save(). >>> q.question_text = "What's up?" >>> q.save() # objects.all() displays all the questions in the database. >>> Question.objects.all() [<Question: Question object>]
Wait a minute.
<Question: Question object> is, utterly, an unhelpful representation
of this object. Let’s fix that by editing the
Question model (in the
polls/models.py file) and adding a
__str__() method to both
from django.db import models class Question(models.Model): # ... def __str__(self): # __unicode__ on Python 2 return self.question_text class Choice(models.Model): # ... def __str__(self): # __unicode__ on Python 2 return self.choice_text
It’s important to add
__str__() methods to your
models, not only for your own convenience when dealing with the interactive
prompt, but also because objects’ representations are used throughout Django’s
On Python 3, it’s easy, just use
On Python 2, you should define
unicode values instead. 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
str(p) will return a bytestring, with characters encoded
as UTF-8. Python does the opposite:
object has a
method that calls
__str__ and interprets the result as an ASCII
bytestring. This difference can create confusion.
If all of this is gibberish to you, just use Python 3.
Note these are normal Python methods. Let’s add a custom method, just for demonstration:
import datetime from django.db import models from django.utils import timezone class Question(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 Question, Choice # Make sure our __str__() addition worked. >>> Question.objects.all() [<Question: What's up?>] # Django provides a rich database lookup API that's entirely driven by # keyword arguments. >>> Question.objects.filter(id=1) [<Question: What's up?>] >>> Question.objects.filter(question_text__startswith='What') [<Question: What's up?>] # Get the question that was published this year. >>> from django.utils import timezone >>> current_year = timezone.now().year >>> Question.objects.get(pub_date__year=current_year) <Question: What's up?> # Request an ID that doesn't exist, this will raise an exception. >>> Question.objects.get(id=2) Traceback (most recent call last): ... DoesNotExist: Question 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 Question.objects.get(id=1). >>> Question.objects.get(pk=1) <Question: What's up?> # Make sure our custom method worked. >>> q = Question.objects.get(pk=1) >>> q.was_published_recently() True # Give the Question 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 question's choice) which can be accessed via the API. >>> q = Question.objects.get(pk=1) # Display any choices from the related object set -- none so far. >>> q.choice_set.all()  # Create three choices. >>> q.choice_set.create(choice_text='Not much', votes=0) <Choice: Not much> >>> q.choice_set.create(choice_text='The sky', votes=0) <Choice: The sky> >>> c = q.choice_set.create(choice_text='Just hacking again', votes=0) # Choice objects have API access to their related Question objects. >>> c.question <Question: What's up?> # And vice versa: Question objects get access to Choice objects. >>> q.choice_set.all() [<Choice: Not much>, <Choice: The sky>, <Choice: Just hacking again>] >>> q.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 question whose pub_date is in this year # (reusing the 'current_year' variable we created above). >>> Choice.objects.filter(question__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 = q.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.