问如何使用新的Django迁移向模型添加新字段？

EN

from django.db.models import CharField
from django.db.models.signals import class_prepared

def add_field(sender, **kwargs):
    """
    class_prepared signal handler that checks for the model named
    MyModel as the sender, and adds a CharField
    to it.
    """
    if sender.__name__ == "MyModel":
        field = CharField("New field", max_length=100)
        field.contribute_to_class(sender, "new_field")

class_prepared.connect(add_field)