Models

Question 1

field as primary key

Answer 1

from django.db import models

class Fruit(models.Model):
    name = models.CharField(max_length=100, primary_key=True)

Question 2

Meta example

Answer 2

from django.db import models

class Ox(models.Model):
    horn_length = models.IntegerField()

    class Meta:
        ordering = ["horn_length"]
        verbose_name_plural = "oxen"

Question 3

raw sql

Answer 3

Person.objects.raw(‘SELECT * FROM myapp_person WHERE last_name = %s’, [lname])

Question 4

Multi-table inheritance

Answer 4

from django.db import models

class Place(models.Model):
    name = models.CharField(max_length=50)
    address = models.CharField(max_length=80)

class Restaurant(Place):
    serves_hot_dogs = models.BooleanField(default=False)
    serves_pizza = models.BooleanField(default=False)

Question 5

Abstract base class

Answer 5

from django.db import models

class CommonInfo(models.Model):
    name = models.CharField(max_length=100)
    age = models.PositiveIntegerField()

    class Meta:
        abstract = True

class Student(CommonInfo):
    home_group = models.CharField(max_length=5)

Question 6

proxy model

Answer 6

from django.db import models

class Person(models.Model):
    first_name = models.CharField(max_length=30)
    last_name = models.CharField(max_length=30)

class MyPerson(Person):
    class Meta:
        proxy = True

    def do_something(self):
        # ...
        pass

Question 7

exact

Answer 7

Entry.objects.get(headline__exact=”Cat bites dog”)

Blog.objects.get(name__iexact=”beatles blog”)

Question 8

contains

Answer 8

Blog.objects.filter(entry__headline__contains=’Lennon’)

Question 9

F expression

Answer 9

> > > from django.db.models import F

|&raquo_space;> Entry.objects.filter(number_of_comments__gt=F(‘number_of_pingbacks’))

Question 10

Q objects

Answer 10

Poll.objects.get(
Q(question__startswith=’Who’),
Q(pub_date=date(2005, 5, 2)) | Q(pub_date=date(2005, 5, 6))
)

Question 11

annotate

Answer 11

> > > from django.db.models import Q
above_5 = Count(‘book’, filter=Q(book__rating__gt=5))
below_5 = Count(‘book’, filter=Q(book__rating__lte=5))
pubs = Publisher.objects.annotate(below_5=below_5).annotate(above_5=above_5)
pubs[0].above_5
23
pubs[0].below_5

Question 12

aggregate

Answer 12

> > > from django.db.models import FloatField
Book.objects.aggregate(
… price_diff=Max(‘price’, output_field=FloatField()) - Avg(‘price’))
{‘price_diff’: 46.85}