从 django 1.5 升级到 1.7 后测试中的异常

Question

这是失败的测试：

def test_registering_user_twice_cause_error_msg(self):

    user=User(name='pyRock',email='python@rocks.com')
    user.save()

    #create the request used to test the view
    self.request.session = {}
    self.request.method = 'POST'
    self.request.POST = {
        'email':'python@rocks.com',
        'name':'pyRock',
        'stripe_token':'...',
        'last_4_digits':'4242',
        'password':'bad_password',
        'ver_password':'bad_password'
    }

    expected_form=UserForm(self.request.POST)
    expected_form.is_valid()
    expected_form.addError('python@rocks.com is already a member')

    #create the expected html
    html = render_to_response(
        'register.html',
        {
            'form': expected_form,
            'months': range(1, 12),
            'publishable': settings.STRIPE_PUBLISHABLE,
            'soon': soon(),
            'user': None,
            'years': list(range(2011, 2036)),
        }
    )

    #mock out stripe so we don't hit their server
    with mock.patch('stripe.Customer') as stripe_mock:

        config = {'create.return_value': mock.Mock()}
        stripe_mock.configure_mock(**config)

        #run the test
        resp = register(self.request)

        #verify that we did things correctly

        self.assertEqual(resp.status_code, 200)
        self.assertEqual(self.request.session, {})
        self.assertEqual(resp.content, html.content)

        #assert there is no records in the database.
        users = User.objects.filter(email="python@rocks.com")
        self.assertEqual(len(users), 1)

所以在运行测试时会抛出以下内容：

ERROR: test_registering_user_twice_cause_error_msg (payments.tests.RegisterPageTests)
----------------------------------------------------------------------
Traceback (most recent call last):
  File "/Users/1111/_realpython/d3/django_ecommerce/payments/tests.py", line 278, in test_registering_user_twice_cause_error_msg
    self.assertEqual(len(users), 1)
  File "/Users/1111/.virtualenvs/d317/lib/python2.7/site-packages/django/db/models/query.py", line 122, in __len__
    self._fetch_all()
  File "/Users/1111/.virtualenvs/d317/lib/python2.7/site-packages/django/db/models/query.py", line 966, in _fetch_all
    self._result_cache = list(self.iterator())
  File "/Users/1111/.virtualenvs/d317/lib/python2.7/site-packages/django/db/models/query.py", line 265, in iterator
    for row in compiler.results_iter():
  File "/Users/1111/.virtualenvs/d317/lib/python2.7/site-packages/django/db/models/sql/compiler.py", line 700, in results_iter
    for rows in self.execute_sql(MULTI):
  File "/Users/1111/.virtualenvs/d317/lib/python2.7/site-packages/django/db/models/sql/compiler.py", line 786, in execute_sql
    cursor.execute(sql, params)
  File "/Users/1111/.virtualenvs/d317/lib/python2.7/site-packages/django/db/backends/utils.py", line 59, in execute
    self.db.validate_no_broken_transaction()
  File "/Users/1111/.virtualenvs/d317/lib/python2.7/site-packages/django/db/backends/__init__.py", line 386, in validate_no_broken_transaction
    "An error occurred in the current transaction. You can't "
TransactionManagementError: An error occurred in the current transaction. You can't execute queries until the end of the 'atomic' block.

我阅读了一些关于 Django 将每个测试包装在事务中的答案，但由于我是 Django 菜鸟，我无法从中得出任何结论，上面的代码就是教程。

更有趣的是，异常发生在断言中。如果我删除它，测试通过，即使查询 users = User.objects.filter(email="python@rocks.com") 存在。但是，如果我以某种方式引用 users，就说 print users，测试会再次中断。

那么发生了什么？

谢谢！

Answer 1

那么发生了什么？

如上所述，this is a duplicate。

但是，如果您访问 users，我将单独说明它中断的原因。发生这种情况的原因是 Django 数据库调用是惰性的，并且会延迟执行，直到您最终使用查询。

因此，如果您从不使用或遍历 users，它将为您节省数据库调用。这就是为什么它看起来可以工作的原因，因为如果你删除 len(users) 它永远不需要 users 的结果，所以不会查询它。