name = models.CharField(max_length=50)
执行：python manage.py makemirations出现以下错误：
You are trying to add a non-nullable field 'name' to contact 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
Select an option:
Reason: Because a new field is added, and the previous data must have no value, but this field cannot be empty, so a default value is required. Alternatively, this field can be allowed to be empty.
Solution:
first give any initial value of 'name': name = models.CharField(max_length=50, default='')
and then execute: python manage.py makemirations
and then execute: python manage.py migrate and
then delete default, that is Execute: name = models.CharField(max_length=50)
Execute: python manage.py makemirations
and then execute: python manage.py migrate
to solve!
Note: During the development process, after the database synchronization misoperation, it is inevitable to encounter the situation that the synchronization cannot be successful later. A simple and rude way to solve this problem is to delete all the scripts in the migrations directory (except __init__.py) Delete the database, create a new database after deleting the database, and do the database synchronization operation again.