Django automatically inheriting "abstract = true" from an abstract meta class

I am using the following code.

class CommonFunctions(object):

    def get_absolute_url(self):
        return "/{0}/list/".format(self.__class__.__name__).lower()

    def get_fields(self):
        return [(field, field.value_to_string(self)) for field in   (self.__class__)._meta.fields]

    class Meta:
          abstract = True

The class is

class Book(models.Model, CommonFunctions):
        book_name = models.CharField(max_length=30)
        book_area = models.CharField(max_length=30)

Now if I use this I get an error,

ForeignKey cannot define a relation with abstract class

But if I use

 class Meta:
      abstract = False

in the Book class then it works.

Why is it inheriting true if their documentati开发者_Python百科on says it should inherit false?

Django does make one adjustment to the Meta class of an abstract base class: before installing the Meta attribute, it sets abstract=False. This means that children of abstract base classes don't automatically become abstract classes themselves.

Your CommonFunctions should be based on models.Model, not object. This way, you will get the behavior stated in the Django documentation.

class CommonFunctions(models.Model):

    def get_absolute_url(self):
        return "/{0}/list/".format(self.__class__.__name__).lower()

    def get_fields(self):
        return [(field, field.value_to_string(self)) for field in   (self.__class__)._meta.fields]

    class Meta:
          abstract = True

And then your Book class should be based only on CommonFunctions.

class Book(CommonFunctions):
    book_name = models.CharField(max_length=30)
    book_area = models.CharField(max_length=30)