Question

我有两个模型，使用多表继承：

# models.py - psuedo-ish code for illustrative purposes

class BaseModel(models.Model):
    name = models.CharField()


class SubclassModel(BaseModel):
    subclass_attr = models.CharField()

我正在测试更新现有SubclassModel实例所需的数据库查询数。计数似乎根据是否在BaseModel或SubclassModel中定义要更改的属性而有所不同。使用debugsqlshell，我得到以下内容：

-- sm is an existing instance of SubclassModel, which has already been saved
-- Note that I'm updating an attribute defined in the BaseModel
>>> sm.name = "Name"
>>> sm.save()
SELECT (1) AS `a`
FROM `app_basemodel`
WHERE `app_basemodel`.`id` = 3 LIMIT 1  [0.40ms]

UPDATE `app_basemodel`
SET `name` = 'Name'
WHERE `app_basemodel`.`id` = 3  [0.34ms]

SELECT (1) AS `a`
FROM `app_subclassmodel`
WHERE `app_subclassmodel`.`basemodel_ptr_id` = 3 LIMIT 1  [0.33ms]

UPDATE `app_subclassmodel`
SET `subclass_attr` = 'something'
WHERE `app_subclassmodel`.`basemodel_ptr_id` = 3  [0.33ms]

对我来说，这看起来像4个查询（SELECT，UPDATE，SELECT，UPDATE）。但是，assertNumQueries只有在设置为3时才会通过我的单元测试：

with self.assertNumQueries(3):
    # update a BaseModel attribute
    sm.name = "Different Name"
    sm.save()

奇怪的是，如果我更新SubclassModel中定义的属性，则SQL看起来完全相同，但assertNumQueries(4)通过。

在SQLite和MySQL上运行测试套件时，行为是一样的。

Django TestCase.assertNumQueries - 对象保存的查询数的意外计数

0 个答案: