Add QuerySet support __bool__

* Add QuerySet support __bool__

* Fix __bool__

* Add pragma no cover

tests/test_queryset.py

@@ -39,6 +39,15 @@ def test_len(qs):
     assert len(qs) == 4
 
 
+@pytest.mark.parametrize('additional_qs, result', [
+    ({}, True),
+    ({'i': {'$gte': 6}}, True),
+    ({'i': {'$gte': 1000}}, False),
+])
+def test_bool_(qs, additional_qs, result):
+    assert bool(qs.find(additional_qs)) is result
+
+
 @pytest.mark.parametrize('slice, result', [
     (slice(None, 2), [6, 7]),
     (slice(2, None), [8, 9]),

yadm/queryset.py

@@ -282,6 +282,9 @@ def __iter__(self):
     def __contains__(self, document):
         raise NotImplementedError
 
+    def __bool__(self):  # pragma: no cover
+        raise NotImplementedError
+
     def find_one(self, criteria=None, projection=None, *, exc=None):
         raise NotImplementedError
 
@@ -324,6 +327,10 @@ def __len__(self):
     def __contains__(self, document):
         return self.find_one(document.id) is not None
 
+    def __bool__(self):
+        qs = self.copy(sort=[], projection={'_id': True})
+        return qs.find_one() is not None
+
     def _get_one(self, index):
         return self._from_mongo_one(self._cursor[index])