如何在 Django 上模拟关系

Question

I'm currently running into a problem, I can't figure out how to mock a relation.

Let's say I have some model called

class MyModel(models.Model):
    name = models.CharField(max_length=10)


class RelatedModel(models.Model):
    my_model = models.OneToOneField(MyModel, on_delete=models.CASCADE, related_name='related_model')
    name = models.CharField(max_length=10

And I have some repository class like this:

class MyModelRepository:
    @staticmethod
    def get_related_model(my_model):
        try:
            return my_model.related_model
        except MyModel.related_model.RelatedObjectDoesNotExist:
            # do some other thing

When writing unit-tests for this how can I mock the related_model to raise this exception or return some arbitrary instance?

Answer 1

Here's a way to do it without unittest.mock :

class MockRelatedModel:
    @property
    def related_model(self):
        raise MyModel.related_model.RelatedObjectDoesNotExist()

If you do want to use unittest.mock you can use PropertyMock . Note, this hasn't been tested. And frankly, I think it might be easier to create an instance of MyModel without the related_model set on it and call MyModelRepository.get_related_model .

with patch('path.to.MyModel', new_callable=PropertyMock) as mock_model:
    mock_model.related_model.side_effect = MyModel.related_model.RelatedObjectDoesNotExist()
    instance = MyModel()
    MyModelRepository.get_related_model(instance)