Question

I’m totally new to django, coming from a PHP perspective. I want to write a real basic application with four classes: Book, Ebook, Genre and price. Each Book and Ebook should have one genre and many prizes. In a SQL-DB I’d put a field in Book and Ebook referencing to a genre table by id and a new table called something like Book_prices which is linking Books and Ebooks to prices.

table book_prices
id | type   | price
---+--------+------ 
1  |  book  | 3
2  |  book  | 3 
3  |  ebook | 1

table book/ebook
id | ... | genre_id
---+-----+---------
1  |     | 5
2  |     | 7
3  |     | 9

Basically I want to add a list of prices and ONE genre for each Ebook and Book. How can I do this using the django model? I know of model.ForeignKey() which could be applied to each Book/Ebook referencing to a genre. But what about my prices? If I add a ForeignKey() to a price it can only reference to a Book OR Ebook.

class Book:
    name = models.CharField(max_length=100)
    pages = models.IntegerField()

class Ebook:
    name = models.CharField(max_length=100)
    filesize = models.FloatField()

class Genre:
    name = models.CharField(max_length=100)
    info = models.TextField()

class Price:
    currency = models.CharField(max_length=4)
    amount = models.FloatField()

Answer 1

Here’s one way. It uses inheritance to reduce duplication between classes.
It uses the contenttypes framework.
Also your classes need to subclass django.db.models

from django.db import models
from django.contrib.contenttypes.models import ContentType
from django.contrib.contenttypes import generic

class Genre(models.Model):
    name = models.CharField(max_length=100)
    info = models.TextField()

class Price(models.Model):
    currency = models.CharField(max_length=4)
    amount = models.FloatField()
    content_type = models.ForeignKey(ContentType)
    object_id = models.PositiveIntegerField()
    book = generic.GenericForeignKey('content_type', 'object_id')

class BookBase(models.Model):
    name = models.CharField(max_length=100) 
    genre = models.ForeignKey(Genre)

    class Meta:
        abstract = True

class Book(BookBase):
    pages = models.IntegerField()

class Ebook(models.Model):
    filesize = models.FloatField()