tastypie problem

gistfile1.txt

    #models.py
    class StoreType(models.Model):
        name = models.CharField(max_length=24, unique=True)
        class Meta:
            ordering = ["name"]
        def __unicode__(self):
            return ("%24s" % (self.name))
       
    class Store(models.Model):
        name = models.CharField(max_length=24)
        store_type = models.ForeignKey(StoreType, to_field='name')
        class Meta:
            ordering = ["store_type", "name"]
            unique_together = (("name", "store_type"),)
        def __unicode__(self):
            return ("%24s (%24s)" % (self.name, self.store_type))
     
    #api.py
    class StoreTypeResource(ModelResource):
        class Meta:
            queryset = StoreType.objects.all()
            resource_name = 'storetype'
            authorization = Authorization()
     
    class StoreResource(ModelResource):
        store_type = fields.ToOneField(StoreTypeResource, 'name', full=True)
        class Meta:
            queryset = Store.objects.all()
            resource_name = 'store'
            authorization = Authorization()
     
    ##### Error
    http://localhost:8000/api/v1/store/?format=json
    {"error_message": "'unicode' object has no attribute 'pk'", "traceback": "Traceback (most recent call last):\n\n  File \"/usr/local/lib/python2.7/dist-packages/tastypie/resources.py\", line 192, in wrapper\n    response = callback(request, *args, **kwargs)\n\n  File \"/usr/local/lib/python2.7/dist-packages/tastypie/resources.py\", line 397, in dispatch_list\n    return self.dispatch('list', request, **kwargs)\n\n  File \"/usr/local/lib/python2.7/dist-packages/tastypie/resources.py\", line 427, in dispatch\n    response = method(request, **kwargs)\n\n  File \"/usr/local/lib/python2.7/dist-packages/tastypie/resources.py\", line 1037, in get_list\n    to_be_serialized['objects'] = [self.full_dehydrate(bundle) for bundle in bundles]\n\n  File \"/usr/local/lib/python2.7/dist-packages/tastypie/resources.py\", line 654, in full_dehydrate\n    bundle.data[field_name] = field_object.dehydrate(bundle)\n\n  File \"/usr/local/lib/python2.7/dist-packages/tastypie/fields.py\", line 633, in dehydrate\n    return self.dehydrate_related(fk_bundle, self.fk_resource)\n\n  File \"/usr/local/lib/python2.7/dist-packages/tastypie/fields.py\", line 514, in dehydrate_related\n    return related_resource.full_dehydrate(bundle)\n\n  File \"/usr/local/lib/python2.7/dist-packages/tastypie/resources.py\", line 660, in full_dehydrate\n    bundle.data[field_name] = method(bundle)\n\n  File \"/usr/local/lib/python2.7/dist-packages/tastypie/resources.py\", line 798, in dehydrate_resource_uri\n    return self.get_resource_uri(bundle)\n\n  File \"/usr/local/lib/python2.7/dist-packages/tastypie/resources.py\", line 1967, in get_resource_uri\n    kwargs['pk'] = bundle_or_obj.obj.pk\n\nAttributeError: 'unicode' object has no attribute 'pk'\n"}