错误models.py Django

Question

I have an error when creating migrations in django

models.py

class StateBuyers(models.Model):
    name = models.CharField(max_length=100)

    def __unicode__(self):
        return self.name

    class Meta:
        db_table = "states"

class CountiesBuyers (models.Model):
    state = models.ForeignKey(StateBuyers, on_delete=models.CASCADE)
    name = models.CharField(max_length=100)

    def __unicode__(self):
        return self.name

    class Meta:
        db_table = "counties"


class CityBuyers (models.Model):
    state = models.ForeignKey(StateBuyers, on_delete=models.CASCADE)
    county = models.ForeignKey(CountiesBuyers, on_delete=models.CASCADE)
    name = models.CharField(max_length=100)

    def __unicode__(self):
        return self.name

    class Meta:
        db_table = "cities"

maybe here I have the error create one instance of many

class Buyers(models.Model):
    name = models.CharField(max_length= 50)
    state = models.ForeignKey(StateBuyers, related_name="Buyers", null=True, on_delete=models.CASCADE)
    city = models.ForeignKey(CityBuyers, related_name="Buyers", null=True, on_delete=models.CASCADE)
    phonenumber = models.CharField(max_length=15)
    email = models.EmailField (max_length= 50)
    notes = models.CharField(max_length=200)

    def __unicode__(self):
        return self.name

    class Meta:
        db_table = "buyers"

At the time of migration throws this error Any ideas ?.

migration error

Answer 1

slightly off-topic, but why do you not follow the conventions?

• simple model names using singular form
• no need for extra parameters if they are same as defaults
• why duplicate State if there is State for county? any performance gains?

class NameAsReprMixin(object):
    def __unicode__(self):
        return self.name

class State(models.Model, NameAsReprMixin):
    name = models.CharField(max_length=100)    


class County(models.Model, NameAsReprMixin):
    state = models.ForeignKey(State)
    name = models.CharField(max_length=100)


class City(models.Model, NameAsReprMixin):
    county = models.ForeignKey(County)
    name = models.CharField(max_length=100)


class Buyer(models.Model, NameAsReprMixin):
    name = models.CharField(max_length= 50)
    state = models.ForeignKey(State, related_name="buyers", null=True)
    city = models.ForeignKey(City, related_name="buyers", null=True)
    phone_number = models.CharField(max_length=15)
    email = models.EmailField(max_length= 50)
    notes = models.CharField(max_length=200)

then:

# all city buyers
City.object.get(...).buyers.all()

# all state byuers
State.object.get(...).buyers.all()