django初始化数据库报Cannot add foreign key constraint

现象描述：

  File "C:\Python38\lib\site-packages\pymysql\cursors.py", line 163, in execute
    result = self._query(query)
  File "C:\Python38\lib\site-packages\pymysql\cursors.py", line 321, in _query
    conn.query(q)
  File "C:\Python38\lib\site-packages\pymysql\connections.py", line 505, in query
    self._affected_rows = self._read_query_result(unbuffered=unbuffered)
  File "C:\Python38\lib\site-packages\pymysql\connections.py", line 724, in _read_query_result
    result.read()
  File "C:\Python38\lib\site-packages\pymysql\connections.py", line 1069, in read
    first_packet = self.connection._read_packet()
  File "C:\Python38\lib\site-packages\pymysql\connections.py", line 676, in _read_packet
    packet.raise_for_error()
  File "C:\Python38\lib\site-packages\pymysql\protocol.py", line 223, in raise_for_error
    err.raise_mysql_exception(self._data)
  File "C:\Python38\lib\site-packages\pymysql\err.py", line 107, in raise_mysql_exception
    raise errorclass(errno, errval)
django.db.utils.IntegrityError: (1215, 'Cannot add foreign key constraint')

 解决办法：

原因是初始化模型有优先次序，要先初始化主模型表，再初始化引入模型表，根据自己的应用，调整下自己子系统的顺序，

例如auth子系统要引入contenttypes子系统的表，如果两个两个子系统先后次序交换，例如：

INSTALLED_APPS = (
    "django.contrib.auth",
    "django.contrib.contenttypes",
    "django.contrib.sessions",
)

就会报错，应该改成：

INSTALLED_APPS = (
    "django.contrib.contenttypes",
    "django.contrib.auth",
    "django.contrib.sessions",
)

调整下子系统中表的次序，尤其在初始化表数据的时候，主模型表还没创建，就新增数据，肯定是会报错的，可以给模型排序