django admin how to limit selectbox values

Question

model:

class Store(models.Model):
  name = models.CharField(max_length = 20)
  class Admin:
    pass
  def __unicode__(self):
    return self.name

class Stock(Store):
  products = models.ManyToManyField(Product)
  class Admin:
    pass
  def __unicode__(self):
    return self.name

class Product(models.Model):
  name = models.CharField(max_length = 128, unique = True)
  parent = models.ForeignKey('self', null = True, blank = True, related_name='children')
  (...)
  def __unicode__(self):
    return self.name

mptt.register(Product, order_insertion_by = ['name'])

admin.py:

from bar.drinkstore.models import Store, Stock

from django.contrib import admin

admin.site.register(Store)
admin.site.register(Stock)

Now when I look at admin site I can select any product from the list. But I'd like to have a limited choice - only leaves. In mptt class there's function:

is_leaf_node() -- returns True if the model instance is a leaf node (it has no children), False otherwise.

But I have no idea how to connect it

I'm trying to make a subclass: in admin.py:

  from bar.drinkstore.models import Store, Stock

  from django.contrib import admin

  admin.site.register(Store)

  class StockAdmin(admin.ModelAdmin):
    def queryset(self, request):
      return super(StockAdmin, self).queryset(request).filter(ihavenoideawhatfilter)

    admin.site.register(Stock, StockAdmin)

but I'm not sure if it's right way, and what filter set.

UPD: This is definetely wrong way. the queryset in class StockAdmin produces list of stocks. But I need to filter product list "on stock" - still don't know how.

Answer 1

So far your idea is right, I'm no expert on how to filter this correctly, but if you look at mptt.models.get_descendant_count you see how the number of descendents i calculated, the leaves are those where the count is zero. I guess you will have to make this condition into raw sql!

EDIT: I just read the title of your question again right now, is it now about seectbox values or changing the queryset for the change list?

Answer 2

Edit: Completely updated this

So the queryset, is finally ok but you need to filter the products on the Stock page select box (I guess?). You can define a custom form for the Stock ModelAdmin.

class StockForm(ModelForm):
    products = forms.ModelChoiceField(queryset=Products.objects.filter(lft=F('rght')-1))
    class Meta:
        model = Stock

class StockAdmin(admin.ModelAdmin):
    form = StockForm

Answer 3

Botondus has the right idea, but you can't do that with annotate - that's for aggregations across related querysets. Try using extra instead:

qs = super(StockAdmin, self).queryset(request).extra(
        select={ 'desc_count': '(rght-lft-1)/2' }
     ).filter(desc_count=0)