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PODjango: cannot detect changes on many-to-many field with m2m_changed signal - auditing at model-level
 

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  1. PODjango: cannot detect changes on many-to-many field with m2m_changed signal - auditing at model-level
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    <p>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.</p> <p>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.</p> <p><strong>Model:</strong></p> <pre><code>from django.contrib.auth.models import User class CustomGroup(models.Model): users = models.ManyToManyField(User, related_name='custom_groups') </code></pre> <p><strong>ModelForm:</strong></p> <pre><code>class CustomUserChangeForm(UserChangeForm): custom_groups = forms.ModelMultipleChoiceField(required=False, queryset=CustomGroup.objects.all()) </code></pre> <p>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:</p> <pre><code>user.custom_groups = self.cleaned_data['custom_groups'] </code></pre> <p>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.</p> <p>Am I doing all this the wrong way? Is there a simpler method that can actually work?</p> <p>Thanks!</p>
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    1. COHere is my solution http://stackoverflow.com/questions/1221878/why-does-django-post-save-signal-give-me-pre-save-data/9172783#9172783
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