1. Creating app

$ 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

1.1 Edit polls/models.py:

from django.db import models

class Question(models.Model):

    question_text = models.CharField(max_length=200)

    pub_date = models.DateTimeField('date published')
  def __str__(self):              # __unicode__ on Python 2

      return self.question_text
  def was_published_recently(self):

      return self.pub_date >= timezone.now()
class Choice(models.Model):    question = models.ForeignKey(Question)    choice_text = models.CharField(max_length=200)    votes = models.IntegerField(default=0)
    def __str__(self):              # __unicode__ on Python 2
     return self.choice_text

1.2 Edit the mysite/settings.py file again, and change the INSTALLED_APPS setting to include the string 'polls':

INSTALLED_APPS = (

    'django.contrib.admin',

    'django.contrib.auth',

    'django.contrib.contenttypes',

    'django.contrib.sessions',

    'django.contrib.messages',

    'django.contrib.staticfiles',

    'polls',

)

1.3 Now Django knows to include the polls app. Let’s run another command:

$ python manage.py makemigrations polls

1.4    Now, run migrate again to create those model tables in your database:

       1.4.1   python manage.py check;

      1.4.2  python manage.pymigrate

1.5    
Playing with the API
     1.5.1   python manage.py shell
     
     1.5.2
>>> 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>]


>>> 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()