Admin inlines very slow to render

[Marc DEBUREAUX]

When using inlines in Django admin, it renders very poorly even when creating a new element (so no data to load, database time always the same).

And the higher the number in "extra" parameter, the longer it takes to load the form.

Works well with Django 1.10

class EffectModifierInline(admin.TabularInline):
    model = EffectModifier
    extra = 1


@admin.register(Effect)
class EffectAdmin(admin.ModelAdmin):
    fieldsets = (
        # Whatever
    )
    inlines = [EffectModifierInline]
    # TODO:
    list_display = ()
    list_editable = ()
    list_filter = ()

    def get_queryset(self, request):
        return super().get_queryset(request).prefetch_related('modifiers')

With 15 inlines

With only 1 inline

With no inline

[sect2k]

I encountered something similar just now, turned out the issue was occurring only when debug-toolbar was enabled.

[Tim Graham]

Yes, the issue is caused by the django-debug-toolbar I believe. See ​https://github.com/jazzband/django-debug-toolbar/issues/910.