我想从makemigrations文件中添加另一个initial.py文件

当我尝试py manage.py makemigrations时显示错误

  

    

您正在尝试向用户添加不可为空的字段“ role”，而没有默认设置；我们无法做到这一点（数据库需要一些东西来填充现有行）。

         

请选择一个修复程序：

         

    

1. 现在提供一个一次性的默认值（将在所有现有行中设置为该列的空值）

    

2. 退出，然后让我在models.py

中添加默认值     

  

我想通过另一个init进行依赖下拉列表

这是我在models.py中写的

import datetime

from django.db import models
from django.utils import timezone

class TableAll(models.Model):
    table_name = models.CharField(max_length=250)

这是0001_initial.py的代码

# Generated by Django 2.2.2 on 2019-10-29 03:52

from django.db import migrations,models
from django.contrib.auth.models import User
import django.db.models.deletion

class Migration(migrations.Migration):

    initial = True

    dependencies = [
    ]

    role = models.CharField(max_length=250)
    role.contribute_to_class(User,'role')    

    operations = [

        migrations.CreateModel(
            name='TableAll',fields=[                
                ('id',models.AutoField(auto_created=True,primary_key=True,serialize=False,verbose_name='ID')),('table_name',models.CharField(max_length=250)),],),]

我想向另一个模型添加外键，并想进行迁移以添加新的00002_initial.py（例如），并且我想要这样的东西（这是我从github源码中找到的代码）

新的初始文件（0002_add_initial_data.py）//这只是github源代码的示例，其中具有0001_initial.py和0002_add_initial_data.py来使依赖的下拉列表起作用

class Migration(migrations.Migration):
    Country = apps.get_model('hr','Country')
    City = apps.get_model('hr','City')

    india = Country.objects.create(name='India')
    City.objects.create(name='Bengaluru',country=india)
    City.objects.create(name='Mumbai',country=india)
    City.objects.create(name='Chennai',country=india)
    City.objects.create(name='Hyderabad',country=india)
    City.objects.create(name='New Delhi',country=india)

    usa = Country.objects.create(name='United States')
    City.objects.create(name='New York',country=usa)
    City.objects.create(name='San Francisco',country=usa)
    City.objects.create(name='Los Angeles',country=usa)
    City.objects.create(name='Chicago',country=usa)
    City.objects.create(name='Seattle',country=usa)

    russia = Country.objects.create(name='Russia')
    City.objects.create(name='Moscow',country=russia)
    City.objects.create(name='Saint Petersburg',country=russia)
    City.objects.create(name='Yekaterinburg',country=russia)
    City.objects.create(name='Kazan',country=russia)
    City.objects.create(name='Krasnodar',country=russia)

    brazil = Country.objects.create(name='Brazil')
    City.objects.create(name='Sao Paulo',country=brazil)
    City.objects.create(name='Rio de Janeiro',country=brazil)
    City.objects.create(name='Belo Horizonte',country=brazil)
    City.objects.create(name='Curitiba',country=brazil)
    City.objects.create(name='Recife',country=brazil)

    uk = Country.objects.create(name='United Kingdom')
    City.objects.create(name='London',country=uk)
    City.objects.create(name='Huddersfield',country=uk)
    City.objects.create(name='Glasgow',country=uk)
    City.objects.create(name='Edinburgh',country=uk)
    City.objects.create(name='Cambridge',country=uk)

    dependencies = [
        ('hr','0001_initial'),]

    operations = [
        migrations.RunPython(add_initial_data),]

感谢您的帮助，这是django框架的新功能，我需要在论文中使用它。.