python - 如何在 Flask-SqlAlchemy 中模拟 .query.filter_by()

Question

简述

在Flask-SqlAlchemy中测试模型类时，如何模拟.query.filter_by()方法返回模拟模型对象列表？

详细信息

假设我们有一个模型类，代码如下

from flask.ext.sqlalchemy import SQLAlchemy
db = SQLAlchemy()
class SomeModel(db.Model):
    # more column mapping and methods go here

然后在我们的 Flask 代码中调用

SomeModel.query.filter_by(...)

在我们的测试代码中，使用Python unittest模型与 mocking ，我们想模拟 filter_by() 调用，以便它返回我们设计的测试用例下的模型对象列表。

我们怎样才能做到这一点？

附注

我的谷歌搜索只找到this related post ;尽管在类(class)开始时应用 @patch("flask_sqlalchemy.SignallingSession", autospec=True) 对我不起作用。

我还尝试模拟如下代码片段的功能

@patch('app.model.some_model.SomeModel.query.filter_by')
def test_some_case(self, filterbyMOCK):
    # more test logic goes here

并且代码在启动时立即出错

RuntimeError: application not registered on db instance and no application bound to current context

PyCharm IDE 的完整错误如下图所示。

Traceback (most recent call last):
  File "/home/namgivu/NN/code/someproject-cloud/venv/local/lib/python2.7/site-packages/mock/mock.py", line 1297, in patched
    arg = patching.__enter__()
  File "/home/namgivu/NN/code/someproject-cloud/venv/local/lib/python2.7/site-packages/mock/mock.py", line 1353, in __enter__
    self.target = self.getter()
  File "/home/namgivu/NN/code/someproject-cloud/venv/local/lib/python2.7/site-packages/mock/mock.py", line 1523, in <lambda>
    getter = lambda: _importer(target)
  File "/home/namgivu/NN/code/someproject-cloud/venv/local/lib/python2.7/site-packages/mock/mock.py", line 1210, in _importer
    thing = _dot_lookup(thing, comp, import_path)
  File "/home/namgivu/NN/code/someproject-cloud/venv/local/lib/python2.7/site-packages/mock/mock.py", line 1197, in _dot_lookup
    return getattr(thing, comp)
  File "/home/namgivu/NN/code/someproject-cloud/venv/local/lib/python2.7/site-packages/flask_sqlalchemy/__init__.py", line 428, in __get__
    return type.query_class(mapper, session=self.sa.session())
  File "/home/namgivu/NN/code/someproject-cloud/venv/local/lib/python2.7/site-packages/sqlalchemy/orm/scoping.py", line 78, in __call__
    return self.registry()
  File "/home/namgivu/NN/code/someproject-cloud/venv/local/lib/python2.7/site-packages/sqlalchemy/util/_collections.py", line 990, in __call__
    return self.registry.setdefault(key, self.createfunc())
  File "/home/namgivu/NN/code/someproject-cloud/venv/local/lib/python2.7/site-packages/flask_sqlalchemy/__init__.py", line 136, in __init__
    self.app = db.get_app()
  File "/home/namgivu/NN/code/someproject-cloud/venv/local/lib/python2.7/site-packages/flask_sqlalchemy/__init__.py", line 809, in get_app
    raise RuntimeError('application not registered on db '
RuntimeError: application not registered on db instance and no application bound to current context

Answer 1

您必须模拟整个映射器类；访问映射器上的 query 属性会导致 session 加载:

@patch('app.model.some_model.SomeModel')
def test_some_case(self, some_model_mock):
    filter_by_mock = some_model_mock.query.filter_by
    # more test logic goes here

那是因为.query属性是一个描述符对象；访问它会触发到 session 的绑定(bind)。

另一种方法是模拟 _QueryProperty.__get__ method (支持 .query 属性)；仅当您必须使用实际的 SomeModel 实例进行测试时才使用它:

@patch('flask_sqlalchemy._QueryProperty.__get__')
def test_some_case(self, query_property_getter_mock):
    filter_by_mock = query_property_getter_mock.return_value.filter_by
    # more test logic goes here

演示:

>>> from flask_sqlalchemy import SQLAlchemy
>>> db = SQLAlchemy()
>>> class SomeModel(db.Model):
...     id = db.Column(db.Integer, primary_key=True)
...
>>> from unittest import mock
>>> with mock.patch('__main__.SomeModel') as model_mock:
...     filter_by = model_mock.query.filter_by
...     SomeModel.query.filter_by(SomeModel.id == 'foo')
...
<MagicMock name='SomeModel.query.filter_by()' id='4438980312'>
>>> with mock.patch('flask_sqlalchemy._QueryProperty.__get__') as query_property_getter_mock:
...     filter_by_mock = query_property_getter_mock.return_value.filter_by
...     SomeModel.query.filter_by(SomeModel.id == 'foo')
...
<MagicMock name='__get__().filter_by()' id='4439035184'>