Django Admin - Filter ManyToManyField with through model

Question

How can I filter a queryset inside the Admin page of an object that has a ManyToManyField relation with a manually defined through model?

Given models.py

class Foo(models.Model):
    foo_field1 = models.CharField(max_length=50)

class Main(models.Model):
    main_field1 = models.CharField(max_length=50)
    m2mfield = models.ManyToManyField(Foo, through="FooBar")

class FooBar(models.Model):
    main = models.ForeignKey(Main, on_delete=models.CASCADE)
    foo = models.ForeignKey(Foo, on_delete=models.CASCADE)
    new_field = models.CharField(max_length=50)

Inside admin.py

class M2MInlineAdmin(admin.TabularInline):
    model = Main.m2mfield.through
    extra = 1

class MainAdmin(admin.ModelAdmin):
   inlines = [M2MInlineAdmin,]
   ...

    def formfield_for_manytomany(self, db_field, request, **kwargs):
        print('called formfield_for_manytomany')
        return super().formfield_for_manytomany(db_field, request, **kwargs)

    def get_field_queryset(self, db, db_field, request):
        print('called get_field_queryset')
        return super().get_field_queryset(db, db_field, request)

I try to access both of these methods, but none of them are called if I specify a through table. However, they do get called if the ManyToMany relation is simply defined as like this:

class Main(models.Model):
    main_field1 = models.CharField(max_length=50)
    m2mfield = models.ManyToManyField(Foo)

Is there a method to filter the queryset when a through table is specified (while being able to access the request context)?

EDIT:

The methods are indeed called when the ManyToManyField has a through model specified, only if there are no fieldsets specified inside the modelAdmin class.

How to access these methods when fieldsets are defined?

Upgraded to 2.2.3 and tested on it. On change/create view, it is always calling formfield_for_manytomany. Not able to reproduce the mentioned scenario. https://github.com/ChillarAnand/library/blob/master/trash/admin.py Can you paste entire model admin code? Is there something else which is missing from the above snippet? — Chillar Anand, Jul 30 '19 at 16:27
@ChillarAnand well, I investigated a bit and noticed that the methods are indeed called, but I am specifying `fieldsets` and for some reason if this variable is defined, the methods are not called... — drec4s, Jul 30 '19 at 17:47

score 2 · Accepted Answer · answered Jul 31 '19 at 15:55

formfield_for_manytomany method seems to be called only when default form is used. When fieldsets is defined, it is using a different form which is why above method is not getting called.

Since you are using tabular admin for many to many field, you can override get_queryset to filter with field.

class M2MInlineAdmin(admin.TabularInline):
    model = Main.fruits.through
    extra = 1

    def get_queryset(self, request):
        qs = super(M2MInlineAdmin, self).get_queryset(request)
        qs = qs.filter(some_arg=some_value)
        return qs

Alternatively, you can write a custom model form and use it in admin instead of default form.

class MainAdminForm(forms.ModelForm):

    class Meta:
        model = Main
        fields = '__all__'

    def __init__(self, *args, **kwargs):
        super().__init__(*args, **kwargs)
        # custom setup


class MainAdmin(admin.ModelAdmin):
    form = MainAdminForm

Thank you, `get_queryset` inside the `TabularInline` did the trick. — drec4s, Jul 31 '19 at 15:59

bromosapien · Answer 2 · 2019-07-25T22:22:19.717

1

You can use the formfield_for_foreignkey() method on the inline class.

class M2MInlineAdmin(admin.TabularInline):
    model = Main.m2mfield.through
    extra = 1

    def formfield_for_foreignkey(self, db_field, request, **kwargs):
        if db_field.name == "car":
            kwargs["queryset"] = Car.objects.filter(owner=request.user)
        return super().formfield_for_foreignkey(db_field, request, **kwargs)

edited Jul 25 '19 at 22:22

answered Jul 25 '19 at 20:15

bromosapien

234
1
5

I need to access the request context while doing this filtering (`object.id` and `request.user`) – drec4s Jul 25 '19 at 20:26
I'm getting `inlineformset_factory() got an unexpected keyword argument 'user'` – drec4s Jul 25 '19 at 20:55
@drec4s did you add the init method above to the custom formset? The user line above `super()` is important. It allows you to use `self.user` in your filtering. – bromosapien Jul 25 '19 at 21:36
yes, copied exactly as you posted, I am setting `self.user` above the `super()` method inside `__init__` – drec4s Jul 25 '19 at 21:42
Wow, I was definitely thinking too hard.. see above for a much easier solution. – bromosapien Jul 25 '19 at 22:23

Django Admin - Filter ManyToManyField with through model

2 Answers2

Linked