我有一个 Salad 型号：

class Salad(models.Model):
    some_field = models.ForeignKey(Profile, on_delete=models.CASCADE, null=True)

不管我怎么称呼这个类，单个字段，我用什么模型来代替它 Profile ，或两者中的任何一个 on_delete 我选择的选项。我得到了一个错误： django.db.utils.IntegrityError: (1215, 'Cannot add foreign key constraint') 错误日志：

Traceback (most recent call last):
  File "C:\Users\Div-o\AppData\Local\Programs\Python\Python35-32\lib\site-packages\django\db\backends\utils.py", line 85, in _execute
  Applying playerdata.0053_auto_20180724_1943...    return self.cursor.execute(sql, params)
  File "C:\Users\Div-o\AppData\Local\Programs\Python\Python35-32\lib\site-packages\django\db\backends\mysql\base.py", line 71, in execute
    return self.cursor.execute(query, args)
  File "C:\Users\Div-o\AppData\Local\Programs\Python\Python35-32\lib\site-packages\MySQLdb\cursors.py", line 250, in execute
    self.errorhandler(self, exc, value)
  File "C:\Users\Div-o\AppData\Local\Programs\Python\Python35-32\lib\site-packages\MySQLdb\connections.py", line 50, in defaulterrorhandler
    raise errorvalue
  File "C:\Users\Div-o\AppData\Local\Programs\Python\Python35-32\lib\site-packages\MySQLdb\cursors.py", line 247, in execute
    res = self._query(query)
  File "C:\Users\Div-o\AppData\Local\Programs\Python\Python35-32\lib\site-packages\MySQLdb\cursors.py", line 411, in _query
    rowcount = self._do_query(q)
  File "C:\Users\Div-o\AppData\Local\Programs\Python\Python35-32\lib\site-packages\MySQLdb\cursors.py", line 374, in _do_query
    db.query(q)
  File "C:\Users\Div-o\AppData\Local\Programs\Python\Python35-32\lib\site-packages\MySQLdb\connections.py", line 292, in query
    _mysql.connection.query(self, query)
_mysql_exceptions.IntegrityError: (1215, 'Cannot add foreign key constraint')

The above exception was the direct cause of the following exception:

Traceback (most recent call last):
  File "C:\Program Files\JetBrains\PyCharm 2017.3.2\helpers\pycharm\django_manage.py", line 52, in <module>
    run_command()
  File "C:\Program Files\JetBrains\PyCharm 2017.3.2\helpers\pycharm\django_manage.py", line 46, in run_command
    run_module(manage_file, None, '__main__', True)
  File "C:\Users\Div-o\AppData\Local\Programs\Python\Python35-32\lib\runpy.py", line 205, in run_module
    return _run_module_code(code, init_globals, run_name, mod_spec)
  File "C:\Users\Div-o\AppData\Local\Programs\Python\Python35-32\lib\runpy.py", line 96, in _run_module_code
    mod_name, mod_spec, pkg_name, script_name)
  File "C:\Users\Div-o\AppData\Local\Programs\Python\Python35-32\lib\runpy.py", line 85, in _run_code
    exec(code, run_globals)
  File "E:/Python/DjangoProjects/rolegate\manage.py", line 15, in <module>
    execute_from_command_line(sys.argv)
  File "C:\Users\Div-o\AppData\Local\Programs\Python\Python35-32\lib\site-packages\django\core\management\__init__.py", line 371, in execute_from_command_line
    utility.execute()
  File "C:\Users\Div-o\AppData\Local\Programs\Python\Python35-32\lib\site-packages\django\core\management\__init__.py", line 365, in execute
    self.fetch_command(subcommand).run_from_argv(self.argv)
  File "C:\Users\Div-o\AppData\Local\Programs\Python\Python35-32\lib\site-packages\django\core\management\base.py", line 288, in run_from_argv
    self.execute(*args,**cmd_options)
  File "C:\Users\Div-o\AppData\Local\Programs\Python\Python35-32\lib\site-packages\django\core\management\base.py", line 335, in execute
    output = self.handle(*args,**options)
  File "C:\Users\Div-o\AppData\Local\Programs\Python\Python35-32\lib\site-packages\django\core\management\commands\migrate.py", line 200, in handle
    fake_initial=fake_initial,
  File "C:\Users\Div-o\AppData\Local\Programs\Python\Python35-32\lib\site-packages\django\db\migrations\executor.py", line 117, in migrate
    state = self._migrate_all_forwards(state, plan, full_plan, fake=fake, fake_initial=fake_initial)
  File "C:\Users\Div-o\AppData\Local\Programs\Python\Python35-32\lib\site-packages\django\db\migrations\executor.py", line 147, in _migrate_all_forwards
    state = self.apply_migration(state, migration, fake=fake, fake_initial=fake_initial)
  File "C:\Users\Div-o\AppData\Local\Programs\Python\Python35-32\lib\site-packages\django\db\migrations\executor.py", line 244, in apply_migration
    state = migration.apply(state, schema_editor)
  File "C:\Users\Div-o\AppData\Local\Programs\Python\Python35-32\lib\site-packages\django\db\backends\base\schema.py", line 90, in __exit__
    self.execute(sql)
  File "C:\Users\Div-o\AppData\Local\Programs\Python\Python35-32\lib\site-packages\django\db\backends\base\schema.py", line 117, in execute
    cursor.execute(sql, params)
  File "C:\Users\Div-o\AppData\Local\Programs\Python\Python35-32\lib\site-packages\django\db\backends\utils.py", line 100, in execute
    return super().execute(sql, params)
  File "C:\Users\Div-o\AppData\Local\Programs\Python\Python35-32\lib\site-packages\django\db\backends\utils.py", line 68, in execute
    return self._execute_with_wrappers(sql, params, many=False, executor=self._execute)
  File "C:\Users\Div-o\AppData\Local\Programs\Python\Python35-32\lib\site-packages\django\db\backends\utils.py", line 77, in _execute_with_wrappers
    return executor(sql, params, many, context)
  File "C:\Users\Div-o\AppData\Local\Programs\Python\Python35-32\lib\site-packages\django\db\backends\utils.py", line 85, in _execute
    return self.cursor.execute(sql, params)
  File "C:\Users\Div-o\AppData\Local\Programs\Python\Python35-32\lib\site-packages\django\db\utils.py", line 89, in __exit__
    raise dj_exc_value.with_traceback(traceback) from exc_value
  File "C:\Users\Div-o\AppData\Local\Programs\Python\Python35-32\lib\site-packages\django\db\backends\utils.py", line 85, in _execute
    return self.cursor.execute(sql, params)
  File "C:\Users\Div-o\AppData\Local\Programs\Python\Python35-32\lib\site-packages\django\db\backends\mysql\base.py", line 71, in execute
    return self.cursor.execute(query, args)
  File "C:\Users\Div-o\AppData\Local\Programs\Python\Python35-32\lib\site-packages\MySQLdb\cursors.py", line 250, in execute
    self.errorhandler(self, exc, value)
  File "C:\Users\Div-o\AppData\Local\Programs\Python\Python35-32\lib\site-packages\MySQLdb\connections.py", line 50, in defaulterrorhandler
    raise errorvalue
  File "C:\Users\Div-o\AppData\Local\Programs\Python\Python35-32\lib\site-packages\MySQLdb\cursors.py", line 247, in execute
    res = self._query(query)
  File "C:\Users\Div-o\AppData\Local\Programs\Python\Python35-32\lib\site-packages\MySQLdb\cursors.py", line 411, in _query
    rowcount = self._do_query(q)
  File "C:\Users\Div-o\AppData\Local\Programs\Python\Python35-32\lib\site-packages\MySQLdb\cursors.py", line 374, in _do_query
    db.query(q)
  File "C:\Users\Div-o\AppData\Local\Programs\Python\Python35-32\lib\site-packages\MySQLdb\connections.py", line 292, in query
    _mysql.connection.query(self, query)
django.db.utils.IntegrityError: (1215, 'Cannot add foreign key constraint')