我正在尝试使用django 2.2.4/sqlite3 2.6.0/python 3.6.8测试一些简单的抽象mixin。
目前，我在使用模式编辑器从测试数据库中删除模型时遇到了问题。
我有以下测试用例：

from django.test import TestCase
from django.db.models.base import ModelBase
from django.db import connection

class ModelMixinTestCase(TestCase):
    """
    Test Case for abstract mixin models.
    """
    mixin = None
    model = None

    @classmethod
    def setUpClass(cls) -> None:
        # Create a real model from the mixin
        cls.model = ModelBase(
            "__Test" + cls.mixin.__name__,
            (cls.mixin,),
            {'__module__': cls.mixin.__module__}
        )

        # Use schema_editor to create schema
        with connection.schema_editor() as editor:
            editor.create_model(cls.model)

        super().setUpClass()

    @classmethod
    def tearDownClass(cls) -> None:
        # Use schema_editor to delete schema
        with connection.schema_editor() as editor:
            editor.delete_model(cls.model)

        super().tearDownClass()

可以这样使用：

class MyMixinTestCase(ModelMixinTestCase):
    mixin = MyMixin

    def test_true(self):
        self.assertTrue(True)

这允许创建和测试模型。问题是在ModelMixinTestCase.tearDownClass中，connection.schema_editor()无法禁用django.db.backends.sqlite3.base中使用的约束检查：

def disable_constraint_checking(self):
        with self.cursor() as cursor:
            cursor.execute('PRAGMA foreign_keys = OFF')
            # Foreign key constraints cannot be turned off while in a multi-
            # statement transaction. Fetch the current state of the pragma
            # to determine if constraints are effectively disabled.
            enabled = cursor.execute('PRAGMA foreign_keys').fetchone()[0]
        return not bool(enabled)

这导致django.db.backends.sqlite3.schema中的DatabaseSchemaEditor在__enter__中出现异常：

def __enter__(self):
        # Some SQLite schema alterations need foreign key constraints to be
        # disabled. Enforce it here for the duration of the schema edition.
        if not self.connection.disable_constraint_checking():
            raise NotSupportedError(
                'SQLite schema editor cannot be used while foreign key '
                'constraint checks are enabled. Make sure to disable them '
                'before entering a transaction.atomic() context because '
                'SQLite does not support disabling them in the middle of '
                'a multi-statement transaction.'
            )
        return super().__enter__()

因此，基于所有这些，我假设我们处于原子上下文中，但我目前不确定退出该上下文并删除模型的最干净方法是什么。