django admin many-to-many intermediary models using through= and filter_horizontal
Solution 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 ofQuestion
model in models.pyclass 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, useQuestion.tags.through
to refer the M2M model.Note, If you don't use
South
, thensyncdb
is enough; If you do,South
does not like this way and will not freezedate_added
field, you need to manually write migration to add/remove the corresponding column. -
Customize ModelAdmin:
- Don't define
fields
inside customized ModelAdmin, only definefilter_horizontal
. This will bypass the field validation mentioned in Irfan's answer. - Customize
formfield_for_dbfield()
orformfield_for_manytomany()
to make Django admin to usewidgets.FilteredSelectMultiple
for thetags
field. - Customize
save_related()
method inside your ModelAdmin class, like
- Don't define
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 theReverseManyRelatedObjectsDescriptor
field descriptor of ManyToManyField fordate_added
to save M2M instance w/o raise exception.
Solution 2
When you specify an intermediary model using the through argument to a ManyToManyField, the admin will not display a widget by default. This is because each instance of that intermediary model requires more information than could be displayed in a single widget, and the layout required for multiple widgets will vary depending on the intermediate model.
However, you can try including the tags field explicitly by using fields = ('tags',)
in admin. This will cause this validation exception
'QuestionAdmin.fields' can't include the ManyToManyField field 'tags' because 'tags' manually specifies a 'through' model.
This validation is implemented in https://github.com/django/django/blob/master/django/contrib/admin/validation.py#L256
if isinstance(f, models.ManyToManyField) and not f.rel.through._meta.auto_created:
raise ImproperlyConfigured("'%s.%s' "
"can't include the ManyToManyField field '%s' because "
"'%s' manually specifies a 'through' model." % (
cls.__name__, label, field, field))
I don't think that you can bypass this validation unless you implement your own custom field to be used as ManyToManyField.
Solution 3
The docs may have changed since the previous answers were posted. I took a look at the django docs link that @Irfan mentioned and it seems to be a more straight forward then it used to be.
Add an inline class to your admin.py
and set the model to your M2M model
class QuestionTagM2MInline(admin.TabularInline):
model = QuestionTagM2M
extra = 1
set inlines
in your admin class to contain the Inline you just defined
class QuestionAdmin(admin.ModelAdmin):
#...other stuff here
inlines = (QuestionTagM2MInline,)
Don't forget to register this admin class
admin.site.register(Question, QuestionAdmin)
After doing the above when I click on a question I have the form to do all the normal edits on it and below that are a list of the elements in my m2m relationship where I can add entries or edit existing ones.
ecbtln
Updated on June 06, 2022Comments
-
ecbtln about 2 years
This is how my models look:
class QuestionTagM2M(models.Model): tag = models.ForeignKey('Tag') question = models.ForeignKey('Question') date_added = models.DateTimeField(auto_now_add=True) class Tag(models.Model): description = models.CharField(max_length=100, unique=True) class Question(models.Model): tags = models.ManyToManyField(Tag, through=QuestionTagM2M, related_name='questions')
All I really wanted to do was add a timestamp when a given manytomany relationship was created. It makes sense, but it also adds a bit of complexity. Apart from removing the .add() functionality [despite the fact that the only field I'm really adding is auto-created so it technically shouldn't interfere with this anymore]. But I can live with that, as I don't mind doing the extra
QuestionTagM2M.objects.create(question=,tag=)
instead if it means gaining the additional timestamp functionality.My issue is I really would love to be able to preserve my
filter_horizontal
javascript widget in the admin. I know the docs say I can use an inline instead, but this is just too unwieldy because there are no additional fields that would actually be in the inline apart from the foreign key to theTag
anyway.Also, in the larger scheme of my database schema, my
Question
objects are already displayed as an inline on my admin page, and since Django doesn't support nested inlines in the admin [yet], I have no way of selecting tags for a given question.Is there any way to override
formfield_for_manytomany(self, db_field, request=None, **kwargs)
or something similar to allow for my usage of the niftyfilter_horizontal
widget and the auto creation of thedate_added
column to the database?This seems like something that django should be able to do natively as long as you specify that all columns in the intermediate are automatically created (other than the foreign keys) perhaps with
auto_created=True
? or something of the like