Django: limit models.ForeignKey results

Question

I have an order model:

class Order(models.Model):
    profile = models.ForeignKey(Profile, null=True, blank=True)

Which returns all possible profiles for an order, which is not necessary and slowing down the loading of the admin order page.

I want the profile returned to simply be the profile of the user who placed the order. I've tried changing it to:

class Order(models.Model):
    profile = models.ForeignKey(Profile, null=True, blank=True, limit_choices_to={'order': 99999})

which returns the correct profile for order number 99999, but how can I get this dynamically. The Order model is not aware of the 'self', but the order number is contained in the URL.

What is the best way to do this?

If the profile is fixed, it sounds like it shouldn't be editable at all. You could make it a [readonly field](https://docs.djangoproject.com/en/1.9/ref/contrib/admin/#django.contrib.admin.ModelAdmin.readonly_fields), and set the value [when the order is placed](https://docs.djangoproject.com/en/1.9/ref/contrib/admin/#django.contrib.admin.ModelAdmin.save_model). — Alasdair, Apr 22 '16 at 14:18

score 0 · Answer 1 · answered Apr 22 '16 at 14:30

If you are using the Django Admin, you can override the method formfield_for_foreignkey on your ModelAdmin class to modify the queryset for the profile field dinamically based on a GET parameter for instance (as you have access to request inside the method.

Look at this example from the docs (adapted for your case):

class MyModelAdmin(admin.ModelAdmin):
    def formfield_for_foreignkey(self, db_field, request, **kwargs):
        if db_field.name == "profile":
            # You can get the order number from the GET parameter:
            # order = request.GET.get('order')
            # or a fixed number:
            order = '12345'
            kwargs["queryset"] = Profile.objects.filter(order=order)
        return super(MyModelAdmin, self).formfield_for_foreignkey(db_field, request, **kwargs)

Reference in the docs: https://docs.djangoproject.com/en/1.9/ref/contrib/admin/#django.contrib.admin.ModelAdmin.formfield_for_foreignkey

Hmm, I tried adding the above code to my OrderAdmin class but this just results in a 504 Gateway Time-out... — James, Apr 22 '16 at 15:16
Although it sort of works with the order = '12345' line, albeit with the wrong profile attached — James, Apr 22 '16 at 15:18
Can you disable the debug, to see what Exception is being thrown that is causing the 504? — Gustavo Carvalho, Apr 22 '16 at 17:36

score 0 · Answer 2 · answered Aug 08 '16 at 22:08

I took another look at this and it seems to be working, although it seems like a bit of hack! The problem was that the order number doesn't seem to exist in the request so I am parsing the URL requested. I put this in my order admin:

def formfield_for_foreignkey(self, db_field, request, **kwargs):
    if db_field.name == "profile":
        try:
            order = int(filter(str.isdigit, str(request.path_info)))
        except:
            order = request.GET.get('order')
        kwargs["queryset"] = Profile.objects.filter(order=order)
    return super(OrderAdmin, self).formfield_for_foreignkey(db_field, request, **kwargs)

The line that filters the url string for an integer works for the change order page of the admin, but didn't work for the order page overview, so I added the try/except. Any suggestions/improvements welcome!

score 0 · Answer 3 · answered Aug 08 '16 at 22:16

I assume from the context you're referring to the display on the Django Admin page. If you set raw_id_fields = {'my_foreign_key'}

you will get a number, text description of related model (from str) and a nice popup box to open an instance of the admin page for your related models.

You could alternatively use list_select_related = True to get the same behaivour you have now but with a couple of order of magnitudes lower number of queries.

Django: limit models.ForeignKey results

3 Answers3