Django：无法通过m2m_changed信号检测多对多字段的变化 - 在模型级别进行审计 [英] Django: cannot detect changes on many-to-many field with m2m_changed signal - auditing at model-level

问题描述

我想跟踪任何模型的哪个领域发生了变化（即，在模型级别审核，因为它更加原子，而不是像管理员/表单级别，就像django和django-reversion可以已经做的那样）。我可以使用前/后保存/删除信号来做任何事情。但是，我有一个在m2m字段上这样做的问题。

对于下面的代码示例，我在用户更改表单中定义custom_groupsm2m字段，因为它是一个反向关系。例如，当用户将表单保存在管理界面上时，如果custom_groups字段中有更改，我想记录。

型号：

  from django.contrib.auth.models import User 
 
 class CustomGroup（models.Model） ：
 users = models.ManyToManyField（User，related_name ='custom_groups'）
  

ModelForm：

  class CustomUserChangeForm（UserChangeForm）：
 custom_groups = forms.ModelMultipleChoiceField（required = False ，queryset = CustomGroup.objects.all（））
  

使用m2m_changed信号的问题是我可以在使用赋值运算符更新m2m字段的情况下，检查实际发生了什么变化：

  user.custom_groups = self。 clean_data ['custom_groups'] 
  

这是因为内部django将在* custom_groups *上执行clear（） ，之前手动添加所有对象。这将执行前/后清除，然后在m2m字段上保存/保存。

我做错了吗？有一个更简单的方法可以实际工作吗？

谢谢！

解决方案

我有一个类似的问题，我想我可以解决它。我不知道你如何使用m2m_changed，但它应该在models.py上，应该类似于这样：

  signals.m2m_changed.connect（your_function，sender = CustomGroup.users.through）
  

现在，我将创建一个包含该函数的signals.py文件，以下代码将打印您选择的选项：

  def your_function（sender，instance，action，reverse，model，pk_set，** kwargs）：
 if action =='post_add'：
 for pk_set：
 print val 
  

现在，您知道更新的值。我希望这可以解决你的问题。

I'd like to keep track on what field has changed on any model (i.e. audit at model level since it's more atomic, not at admin/form-level like what django and django-reversion can already do). I'm able to do that for any field using pre/post save/delete signals. However, I have a problem of doing that on an m2m field.

For the code sample below, i define 'custom_groups' m2m field in user change form since it's a reverse relation. When user saves the form on admin interface for example, I'd like to log if there's a change in 'custom_groups' field.

Model:

from django.contrib.auth.models import User

class CustomGroup(models.Model):
    users = models.ManyToManyField(User, related_name='custom_groups')

ModelForm:

class CustomUserChangeForm(UserChangeForm):
    custom_groups = forms.ModelMultipleChoiceField(required=False, queryset=CustomGroup.objects.all())

The problem with using m2m_changed signal is that i can't check what has actually changed for the case where the m2m field is updated using assignment operator:

user.custom_groups = self.cleaned_data['custom_groups']

This is because internally django will perform a clear() on *custom_groups*, before manually adding all objects. This will execute pre/post-clear and then pre/post save on the m2m field.

Am I doing all this the wrong way? Is there a simpler method that can actually work?

Thanks!

解决方案

I had a similar problem and I think I could solve it. I don't know how you are using the m2m_changed but it should be on models.py and should be similar to something like this:

signals.m2m_changed.connect(your_function, sender=CustomGroup.users.through)

Now, I would create a signals.py file containing that function, and the following code should print you the options that you have selected:

def your_function(sender, instance, action, reverse, model, pk_set, **kwargs):
    if action == 'post_add':
        for val in pk_set:
            print val

Now, you know the updated values. I hope this could solve your problem.

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