From cb77bb6b69bb80c79c97d2f0792d173fc2f443d4 Mon Sep 17 00:00:00 2001
From: Filip Kucharczyk <filip.m.kucharczyk@gmail.com>
Date: Thu, 5 Dec 2019 00:21:03 +0100
Subject: [PATCH] Implement __bool__ on Q and QCombination

---
 mongoengine/queryset/base.py    |  2 +-
 mongoengine/queryset/visitor.py | 20 ++++++++++++++++----
 tests/queryset/test_visitor.py  | 11 +++++++++++
 3 files changed, 28 insertions(+), 5 deletions(-)

diff --git a/mongoengine/queryset/base.py b/mongoengine/queryset/base.py
index a648391e..c6f467cc 100644
--- a/mongoengine/queryset/base.py
+++ b/mongoengine/queryset/base.py
@@ -686,7 +686,7 @@ class BaseQuerySet(object):
         .. versionchanged:: 0.6 Raises InvalidQueryError if filter has been set
         """
         queryset = self.clone()
-        if not queryset._query_obj.empty:
+        if queryset._query_obj:
             msg = "Cannot use a filter whilst using `with_id`"
             raise InvalidQueryError(msg)
         return queryset.filter(pk=object_id).first()
diff --git a/mongoengine/queryset/visitor.py b/mongoengine/queryset/visitor.py
index 058c722a..a7295ae5 100644
--- a/mongoengine/queryset/visitor.py
+++ b/mongoengine/queryset/visitor.py
@@ -2,6 +2,8 @@ import copy
 
 from mongoengine.errors import InvalidQueryError
 from mongoengine.queryset import transform
+import warnings
+
 
 __all__ = ("Q", "QNode")
 
@@ -101,13 +103,15 @@ class QNode(object):
             return self
 
         # Or if this Q is empty, ignore it and just use `other`.
-        if self.empty:
+        if not self:
             return other
 
         return QCombination(operation, [self, other])
 
     @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 +141,9 @@ 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)
+
     def accept(self, visitor):
         for i in range(len(self.children)):
             if isinstance(self.children[i], QNode):
@@ -146,6 +153,8 @@ 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 +176,15 @@ class Q(QNode):
     def __repr__(self):
         return "Q(**%s)" % repr(self.query)
 
+    def __bool__(self):
+        return bool(self.query)
+
+    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
diff --git a/tests/queryset/test_visitor.py b/tests/queryset/test_visitor.py
index afa00839..81e0f253 100644
--- a/tests/queryset/test_visitor.py
+++ b/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()