You are trying to add a non-nullable field 'Number' to author without a default; we can't do that (the database needs something to populate existing rows). Please select a fix: 1) Provide a one-off default now (will be set on all existing rows with a null value for this column) 2) Quit, and let me add a default in models.py

It seems like you are facing a database migration issue in Django. In this case, you have added a non-nullable field 'Number' to the 'author' model without a default value, and there are existing rows with null values for this column.

To solve this issue, you have two options:

1. Provide a one-off default now: You can provide a default value for the 'Number' field that will be set on all existing rows with a null value for this column. You can do this by running the following command in your Django project directory:

   python manage.py makemigrations --empty yourappname

This will create an empty migration file for your app. Then add the following code to the `operations` list in the `migrations.RunPython` method:

   from django.db import migrations

   def set_default_value(apps, schema_editor):
       Author = apps.get_model('yourappname', 'Author')
       Author.objects.filter(Number=None).update(Number=0)

   class Migration(migrations.Migration):

       dependencies = [
           ('yourappname', 'previous_migration'),
       ]

       operations = [
           migrations.RunPython(set_default_value),
       ]

Replace 'yourappname' and 'previous_migration' with your actual app name and the previous migration name respectively. Then run the following command:

   python manage.py migrate

This will apply the migration and set the default value for the 'Number' field on all existing rows with null values.

2. Quit, and let me add a default in models.py: If you don't want to provide a default value for the 'Number' field, you can quit the migration process and add a default value in the 'author' model in your models.py file. You can do this by adding the following code to your model:

   class Author(models.Model):
       name = models.CharField(max_length=100)
       # Add default value for Number field
       Number = models.IntegerField(default=0)

Then run the following command to create a new migration:

   python manage.py makemigrations

This will create a new migration file with the default value for the 'Number' field. Then run the following command to apply the migration:

   python manage.py migrate

This will apply the migration and add the default value for the 'Number' field in the 'author' model.