I've got a model for Orders in a webshop application, with an auto-incrementing primary key and a foreign key to itself, since orders can be split into multiple orders, but the relationship to the original order must be maintained.
class Order(models.Model):
ordernumber = models.AutoField(primary_key=True)
parent_order = models.ForeignKey('self', null=True, blank=True, related_name='child_orders')
# .. other fields not relevant here
I've registered an OrderAdmin class for the admin site. For the detail view, I've included parent_order in the fieldsets attribute. Of course, by default this lists all the orders in a select box, but this is not the desired behaviour. Instead, for orders that don't have a parent order (i.e. have not been split from another order; parent_order is NULL/None), no orders should be displayed. For orders that have been split, this should only display the single parent order.
There's a rather new ModelAdmin method available, formfield_for_foreignkey, that seems perfect for this, since the queryset can be filtered inside it. Imagine we're looking at the detail view of order #11234, which has been split from order #11208. The code is below
def formfield_for_foreignkey(self, db_field, request, **kwargs):
if db_field.name == 'parent_order':
# kwargs["queryset"] = Order.objects.filter(child_orders__ordernumber__exact=11234)
return db_field.formfield(**kwargs)
return super(OrderAdmin, self).formfield_for_foreignkey(db_field, request, **kwargs)
The commented row works when run in a Python shell, returning a single-item queryset containing order #11208 for #11234 and all other orders that may have been split from it.
Of course, we can't hard-code the order number there. We need a reference to the ordernumber field of the order instance whose detail page we're looking at. Like this:
kwargs["queryset"] = Order.objects.filter(child_orders__ordernumber__exact=?????)
I've found no working way to replace ????? with a reference to the "current" Order instance, and I've dug pretty deep. self inside formfield_for_foreignkey refers to the ModelAdmin instance, and while that does have a model attribute, it's not the order model instance (it's a ModelBase reference; self.model() returns an instance, but its ordernumber is None).
One solution might be to pull the order number from request.path (/admin/orders/order/11234/), but that is really ugly. I really wish there is a better way.
I think you might need to approach this in a slightly different way - by modifying the ModelForm, rather than the admin class. Something like this:
class OrderForm(forms.ModelForm):
def __init__(self, *args, **kwargs):
super(OrderForm, self).__init__(*args, **kwargs)
self.fields['parent_order'].queryset = Order.objects.filter(
child_orders__ordernumber__exact=self.instance.pk)
class OrderAdmin(admin.ModelAdmin):
form = OrderForm