Question

Is there a negation filter available by default. The idea is that you can do the following in the django ORM:

model.objects.filter(field!=value)

How can I do that in tastypie if that is even possible. I tried:

someapi.com/resource/pk/?field__not=value
someapi.com/resource/pk/?field__!=value
someapi.com/resource/pk/?field!=value

And all of them given me errors.

Answer 1

Unfortunately there’s not.

The problem is that Tastypie’s ModelResource class uses the filter() method of the QuerySet only, i.e. it does not use exclude() which should be used for negative filters. There is no filter() field lookup that would mean negation though. The valid lookups are (after this SO post):

exact
iexact
contains
icontains
in
gt
gte
lt
lte
startswith
istartswith
endswith
iendswith
range
year
month
day
week_day
isnull
search
regex
iregex

However it shouldn’t be so hard to implement the support for something like “__not_eq”. All you need to do is to modify the apply_filters() method and separate filters with “__not_eq” from the rest. Then you should pass the first group to exclude() and the rest to filter().

Something like:

def apply_filters(self, request, applicable_filters):
    """
    An ORM-specific implementation of ``apply_filters``.

    The default simply applies the ``applicable_filters`` as ``**kwargs``,
    but should make it possible to do more advanced things.
    """
    positive_filters = {}
    negative_filters = {}
    for lookup in applicable_filters.keys():
        if lookup.endswith( '__not_eq' ):
            negative_filters[ lookup ] = applicable_filters[ lookup ]
        else:
            positive_filters[ lookup ] = applicable_filters[ lookup ]

    return self.get_object_list(request).filter(**positive_filters).exclude(**negative_filters)

instead of the default:

def apply_filters(self, request, applicable_filters):
    """
    An ORM-specific implementation of ``apply_filters``.

    The default simply applies the ``applicable_filters`` as ``**kwargs``,
    but should make it possible to do more advanced things.
    """
    return self.get_object_list(request).filter(**applicable_filters)

should allow for the following syntax:

someapi.com/resource/pk/?field__not_eq=value

I haven’t tested it. It could probably be written in more elegant way too, but should get you going 🙂