Merge pull request #2210 from Pacu2/fix/implement-bool-on-q-and-qcombination

Add __bool__ to Q and QCombination

docs/changelog.rst

@@ -17,6 +17,9 @@ Development
     - If you catch/use ``MongoEngineConnectionError`` in your code, you'll have to rename it.
 - BREAKING CHANGE: Positional arguments when instantiating a document are no longer supported. #2103
     - From now on keyword arguments (e.g. ``Doc(field_name=value)``) are required.
+- DEPRECATION: ``Q.empty`` & ``QNode.empty`` are marked as deprecated and will be removed in a next version of MongoEngine. #2210
+    - Added ability to check if Q or QNode are empty by parsing them to bool.
+    - Instead of ``Q(name="John").empty`` use ``not Q(name="John")``.
 - Improve error message related to InvalidDocumentError #2180
 - Fix updating/modifying/deleting/reloading a document that's sharded by a field with ``db_field`` specified. #2125
 - ``ListField`` now accepts an optional ``max_length`` parameter. #2110

mongoengine/queryset/visitor.py

@@ -1,4 +1,5 @@
 import copy
+import warnings
 
 from mongoengine.errors import InvalidQueryError
 from mongoengine.queryset import transform
@@ -108,6 +109,8 @@ class QNode(object):
 
     @property
     def empty(self):
+        msg = "'empty' property is deprecated in favour of using 'not bool(filter)'"
+        warnings.warn(msg, DeprecationWarning)
         return False
 
     def __or__(self, other):
@@ -137,6 +140,11 @@ class QCombination(QNode):
         op = " & " if self.operation is self.AND else " | "
         return "(%s)" % op.join([repr(node) for node in self.children])
 
+    def __bool__(self):
+        return bool(self.children)
+
+    __nonzero__ = __bool__  # For Py2 support
+
     def accept(self, visitor):
         for i in range(len(self.children)):
             if isinstance(self.children[i], QNode):
@@ -146,6 +154,8 @@ class QCombination(QNode):
 
     @property
     def empty(self):
+        msg = "'empty' property is deprecated in favour of using 'not bool(filter)'"
+        warnings.warn(msg, DeprecationWarning)
         return not bool(self.children)
 
     def __eq__(self, other):
@@ -167,12 +177,17 @@ class Q(QNode):
     def __repr__(self):
         return "Q(**%s)" % repr(self.query)
 
+    def __bool__(self):
+        return bool(self.query)
+
+    __nonzero__ = __bool__  # For Py2 support
+
+    def __eq__(self, other):
+        return self.__class__ == other.__class__ and self.query == other.query
+
     def accept(self, visitor):
         return visitor.visit_query(self)
 
     @property
     def empty(self):
         return not bool(self.query)
-
-    def __eq__(self, other):
-        return self.__class__ == other.__class__ and self.query == other.query

tests/queryset/test_visitor.py

@@ -407,6 +407,17 @@ class TestQ(unittest.TestCase):
     def test_combine_or_both_empty(self):
         assert Q() | Q() == Q()
 
+    def test_q_bool(self):
+        assert Q(name="John")
+        assert not Q()
+
+    def test_combine_bool(self):
+        assert not Q() & Q()
+        assert Q() & Q(name="John")
+        assert Q(name="John") & Q()
+        assert Q() | Q(name="John")
+        assert Q(name="John") | Q()
+
 
 if __name__ == "__main__":
     unittest.main()