django admin many-to-many intermediary models using through= and filter_horizontal

Question

This is how my models look:

class QuestionTagM2M(models.Model):
    tag = models.ForeignKey(\'Tag\')
    question = models.ForeignKey(\'Question\')
    date_         


        

Answer 1

There are ways to do this

• As provided by @obsoleter in the comment below : set QuestionTagM2M._meta.auto_created = True and deal w/ syncdb matters.

• Dynamically add date_added field to the M2M model of Question model in models.py

  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')
  

  Then you could use it in admin as normal ManyToManyField.
  In Python shell, use Question.tags.through to refer the M2M model.

  Note, If you don't use South, then syncdb is enough; If you do, South does not like this way and will not freeze date_added field, you need to manually write migration to add/remove the corresponding column.

• Customize ModelAdmin:

  1. Don't define fields inside customized ModelAdmin, only define filter_horizontal. This will bypass the field validation mentioned in Irfan's answer.
  2. Customize formfield_for_dbfield() or formfield_for_manytomany() to make Django admin to use widgets.FilteredSelectMultiple for the tags field.
  3. Customize save_related() method inside your ModelAdmin class, like

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)

• Also, you could patch __set__() of the ReverseManyRelatedObjectsDescriptor field descriptor of ManyToManyField for date_added to save M2M instance w/o raise exception.