在将数据关联到用户时，在活动状态的虚拟环境中执行迁移命令，结果表明一切顺利。但在shell中验证迁移结果是否符合预期时出现报错。
（ll_env）F:\learning_log>python manage.py migrate
Operations to perform:
Apply all migrations: admin, auth, contenttypes, learning_logs, sessions
Running migrations:
Applying learning_logs.0003_topic_owner… OK
验证时，输入：
from learning_logs.models import Topic
报错：
Traceback (most recent call last):
_snip_
django.core.exceptions.ImproperlyConfigured: Requested setting INSTALLED_APPS, but settings are not configured. You must either define the environment variable DJANGO_SETTINGS_MODULE or call settings.configure() before accessing settings.
