$ python manage.py makemigrations You are trying to add a non-nullable field 'name' to course without a default; we can't do that (the database needs something to populate existing rows). Please selec

问题：

$ python manage.py makemigrations
You are trying to add a non-nullable field 'name' to course 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

原因：由于之前已经存在的表，某些字段为没有默认值，这时候添加的时候，需要给定默认值

解决：

方法1：每个报错的字段添加   

blank=True, null=True

方法2：需要添加的字段太多，

         本地自己做项目的话，

       删除之前的数据库，删除migrations,

     重新生成数据