django.db.models.loading.get_model与导入 [英] django.db.models.loading.get_model vs. importing

问题描述

 从django.db.models.loading导入get_model 
 $有什么不利之处？ b $ b def get_something（）：
 model = get_model（'app'，'Model'）
 return model.something（）
  

而不是

 来自app.models import模型
 
 def get_something（）：
 return Model.something（）
  

第二个例子可以导致循环依赖，而第一个例子不是，但第二个例子更经常看到。

更新：你会得到循环依赖性错误，如果第二个例子在一个名为Other_Model的模型中，并且Model导入了Other_Model以及一个简单的循环导入。

解决方案

通常， get_model 功能被保留用于需要动态加载模型的时间（例如，如果您不知道是否有人会通过一个服务myapp.Person，一个myapp.Place或一个myapp.Thing，他们都有相同的界面）。如果没有其他原因导致意想不到的事实，我将会说，任何其他用途应该在代码审查中自动标记。

As对于内部力学，真的没有什么大的差别。不可避免地， get_model 版本将调用 __ import __ 。也就是说，它不是没有bug 。使用实际的导入语句将避免此问题。

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As对于MRO问题，通过重构无法解决循环进口是一种罕见的情况。如果你有两个应用程序是如此相互依赖的，它们导致循环导入，那么你真的需要重新考虑这些应用程序。 （我的猜测是，你真的在​​处理一个应用程序。）

Is there any downside to using something like

from django.db.models.loading import get_model

def get_something():
    model = get_model('app', 'Model')
    return model.something()

instead of

from app.models import Model

def get_something():
    return Model.something()

The second example can lead to circular dependencies while the first example does not, but the second example is seen much more often.

Update: You would get circular dependency errors if the second example was in a model called Other_Model and Model imported Other_Model as well -- a simple circular import.

解决方案

Generally, the get_model functionality is reserved for times when a model needs to be loaded dynamically (say, if you don't know if someone will pass a service a myapp.Person, a myapp.Place, or a myapp.Thing and they all have the same interface). I will go so far as to say that any other use should be auto-flagged in code review if for no other reason than the fact that it introduces the unexpected.

As to internal mechanics, there really isn't a substantial difference. Inevitably the get_model version will call __import__. That said, it is not without bugs. Use of actual import statements will avoid this problem.

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As to MRO issues, it is a rare situation where circular imports could not be resolved by refactoring. If you have two apps which are so interdependent that they cause a circular import, then you really need to re-think those apps. (My guess is that you are really dealing with one app.)

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