Запись данных через форму связанных моделей

Все привет, вопрос, как записать данные в связанную модель? Например есть три модели:

class regSurname(models.Model):
    surname = models.CharField(max_length=500, verbose_name='Фамилия')

class regName(models.Model):
    name = models.CharField(max_length=500, verbose_name='Имя')
    surname_key = models.ForeignKey(regSurname, on_delete=models.CASCADE)

class regPatronymic(models.Model):
    patronymic = models.CharField(max_length=500, verbose_name='Отчество')
    surname_key = models.ForeignKey(regSurname, on_delete=models.CASCADE)

Формы

class regSurnameForm(forms.ModelForm):
    class Meta:
        model = regSurname
        fields = ['school_key', 'surname']
        widgets = {
            'surname': forms.TextInput(attrs={'class': 'reg_input'}),
        }

class regNameForm(forms.ModelForm):
    class Meta:
        model = regName
        fields = ['name']
        widgets = {
            'name': forms.TextInput(attrs={'class': 'reg_input'}),
        }


class regPatronymicForm(forms.ModelForm):
    class Meta:
        model = regPatronymic
        fields = ['patronymic']
        widgets = {
            'patronymic': forms.TextInput(attrs={'class': 'reg_input'}),
        }

При отправке данных "(1048, "Column 'surname_key_id' cannot be null")" СПАСИБО!