Django admin hangs (until timeout error) for a specific model when trying to edit/create

In your admin.py file, under the appropriate admin class, set

raw_id_fields = ('zipcode',)

This will display the zipcode's PK instead of a dropdown.

Is there a reason that you are setting up zipcode as it's own model instead of using a CharField or an actual zipcode modelfield?

I just wanted to add that another option here is creating a read_only_fields list. In cases where there is a relationship to a model with a large number of choices(in my case a rel table cataloging flags between a large number of users and discussion threads) but you don't need to edit the field. You can add it to the read_only_fields list will just print the value rather than the choices.

class FlaggedCommentsAdmin(ModelAdmin):
    list_display = ('user', 'discussion', 'flagged_on')
    readonly_fields = ('user', 'discussion')

For people still landing on this page: As Mamsaac points out in his original post, the timeout happens because django tries to load all instances of a ForeignKey into an html-select. Django 2 lets you add an auto-complete field which asynchronously lets you search for the ForeignKey to deal with this. In your admin.py do something like this:

from django.contrib import admin
from .models import Parent, Child

@admin.register(Parent)
class ParentAdmin(admin.ModelAdmin):
    # tell admin to autocomplete-select the "Parent"-field 'children'
    autocomplete_fields = ['children']

@admin.register(Child)
class ChildAdmin(admin.ModelAdmin):
    # when using an autocomplete to find a child, search in the field 'name'
    search_fields = ['name']