Database API and Django Admin

from polls.models import Question, Choice   # Import the model classes we just wrote.

# currently the database is empty.
Question.objects.all()

# Output: 
#   <Queryset []>

Choice.objects.all()

# Output:
#   <Queryset []>

# Let's create a new Question first
# If you remember the Question model has a pub_date field, which stores a datetime
# Although Python has datetime.datetime.now(),
# we will use the Django's implementation of the same
# which uses the timezone setting to create a datetime
# with timezone info included.
from django.utils import timezone

q = Question(question_text="What would you say, Dear Sir, is up?", pub_date=timezone.now())

# The above statement only creates a Python Model Object.
# To persist it in the database we do the following
q.save();

# Above 2 statements can be combined using the objects.create() method as follows
# It creates the Python model and saves it in Database in a single statement
q = Question.objects.create(question_text="What would you say, Dear Sir, is up?", pub_date=timezone.now())

# Access the model fields as Python attributes
q.id

# Output:
#   1

# Note: In some databases the above value may be 1L instead of just being 1.
# It is completely normal,
# Python read them as Long integers rather than regular integers.

q.question_text

# Output:
#   "What's up?"

q.pub_date

# Output:
#   datetime.datetime(2017, 6, 01, 13, 0, 0, 775217, tzinfo=<UTC>)

# Changing the value is as simple as changing the attributes and then calling save().
q.question_text = "What's up"
q.save()

# To list all the questions in database, we use objects.all().
Question.objects.all()

# Output:
#   <QuerySet [<Question: Question object>]>

# Python Code
# polls/models.py

from django.db import models
from django.utils.encoding import python_2_unicode_compatible

@python_2_unicode_compatible  # only if you need to support Python 2
class Question(models.Model):
    # ...
    def __str__(self):
        return self.question_text

@python_2_unicode_compatible  # only if you need to support Python 2
class Choice(models.Model):
    # ...
    def __str__(self):
        return self.choice_text

from polls.models import Question, Choice

Question.objects.all()

# Output:
#   <QuerySet [<Question: What's up?>]>

# Python Code
# polls/models.py

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)

from polls.models import Question, Choice


# Django provides a rich database lookup API that's entirely driven by
# keyword arguments.
Question.objects.get(id=1)

# Output:
#   <Question: What's up?>


Question.objects.filter(id=1)

# Output:
#   <QuerySet [<Question: What's up?>]>


Question.objects.filter(question_text__startswith='What')

# Output:
#   <QuerySet [<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)

# Output:
#   <Question: What's up?>


# Request an ID that doesn't exist, this will raise an exception.
Question.objects.get(id=2)

# Output:
#   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)

# Output:
#   <Question: What's up?>

# Make sure our custom method worked.
q = Question.objects.get(pk=1)
q.was_published_recently()

# Output:
#   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()

# Output:
#   <QuerySet []>


# Create three choices.
q.choice_set.create(choice_text='Not much', votes=0)

# Output:
#   <Choice: Not much>


q.choice_set.create(choice_text='The sky', votes=0)

# Output:
#   <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

# Output:
#   <Question: What's up?>


# And vice versa: Question objects get access to Choice objects.
q.choice_set.all()

# Output:
#   <QuerySet [<Choice: Not much>, <Choice: The sky>, <Choice: Just hacking again>]>


q.choice_set.count()

# Output:
#   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)

# Output:
#   <QuerySet [<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()

# Python code
# polls/admin.py

from django.contrib import admin

from .models import Question

admin.site.register(Question)