Had to do the same and stumbled upon your question. This is how I fixed it in my code (adapted to your example):
class CanceledFilter(SimpleListFilter):
title = 'Canceled'
# Parameter for the filter that will be used in the URL query.
parameter_name = 'canceled'
def lookups(self, request, model_admin):
return (
(2, 'All'),
(1, 'Yes'),
(0, 'No'),
)
def queryset(self, request, queryset):
if self.value() is None:
self.used_parameters[self.parameter_name] = 0
else:
self.used_parameters[self.parameter_name] = int(self.value())
if self.value() == 2:
return queryset
return queryset.filter(cancelled=self.value())
Some explanation is required. The querystring is just part of the URL, and exactly what the name implies: a query string. Your values come in as strings, not as booleans or integers. So when you call self.value()
, it returns a string.
If you examine the URL you get when you click on the Yes/No, when not using a custom list filter, you'll see it encodes it as 1/0, not True/False. I went with the same scheme.
For completeness and our future readers, I also added 2 for All. Without verifying, I assume that was None
before. But None
is also used when nothing is selected, which defaults to All. Except, in our case it needs to default to False
, so I had to pick a different value. If you don't need the All option, just remove the final if-block in the queryset
method, and the first tuple in the lookups
method.
With that out of the way, how does it work? The trick is in realising that self.value()
just returns:
self.used_parameters.get(self.parameter_name, None)
which is either a string, or None
, depending on whether the key is found in the dictionary or not. So that's the central idea: we make sure it contains integers and not strings, so that self.value()
can be used in the call to queryset.filter()
. Special treatment for the value for All, which is 2: in this case, just return queryset
rather than a filtered queryset. Another special value is None
, which means there is no key parameter_name
in the dictionary. In that case, we create one with value 0, so that False
becomes the default value.
Note: your logic was incorrect there; you want the non-cancelled by default, but you treat None
the same as True
. My version corrects this.
ps: yes, you could check for 'True'
and 'False'
rather than True
and False
in your querystring
method, but then you'd notice the correct selection would not be highlighted because the first elements in your tuple don't match up (you're comparing strings to booleans then). I tried making the first elements in the tuples strings too, but then I'd have to do string comparison or eval
to match up 'True'
to True
, which is kind of ugly/unsafe. So best stick to integers, like in my example.