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copied!<p>There are <em>ways</em> to do this </p> <ul> <li>As provided by @obsoleter in <a href="https://stackoverflow.com/questions/10110606/django-admin-many-to-many-intermediary-models-using-through-and-filter-horizont/10203192?noredirect=1#comment18228487_10203192">the comment below</a> : set <code>QuestionTagM2M._meta.auto_created = True</code> and deal w/ syncdb matters.</li> <li><p>Dynamically add <code>date_added</code> field to the M2M model of <code>Question</code> model in models.py</p> <pre><code>class Question(models.Model): # use auto-created M2M model tags = models.ManyToMany(Tag, related_name='questions') # add date_added field to the M2M model models.DateTimeField(auto_now_add=True).contribute_to_class( Question.tags.through, 'date_added') </code></pre> <p>Then you could use it in admin as normal <code>ManyToManyField</code>.<br> In Python shell, use <code>Question.tags.through</code> to refer the M2M model. </p> <p><em>Note</em>, If you don't use <code>South</code>, then <code>syncdb</code> is enough; If you do, <code>South</code> does not like this way and will not freeze <code>date_added</code> field, you need to manually write migration to add/remove the corresponding column. </p></li> <li><p>Customize ModelAdmin:</p> <ol> <li>Don't define <code>fields</code> inside customized ModelAdmin, only define <code>filter_horizontal</code>. This will bypass the field validation mentioned in Irfan's answer.</li> <li>Customize <code>formfield_for_dbfield()</code> or <code>formfield_for_manytomany()</code> to make Django admin to use <code>widgets.FilteredSelectMultiple</code> for the <code>tags</code> field.</li> <li>Customize <code>save_related()</code> method inside your ModelAdmin class, like</li> </ol></li> </ul> <p></p> <pre><code>def save_related(self, request, form, *args, **kwargs): tags = form.cleaned_data.pop('tags', ()) question = form.instance for tag in tags: QuestionTagM2M.objects.create(tag=tag, question=question) super(QuestionAdmin, self).save_related(request, form, *args, **kwargs) </code></pre> <ul> <li>Also, you could patch <code>__set__()</code> of the <code>ReverseManyRelatedObjectsDescriptor</code> field descriptor of ManyToManyField for <code>date_added</code> to save M2M instance w/o raise exception.</li> </ul>

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