Add __eq__ to Q and Q operations

mongoengine/queryset/visitor.py

@@ -96,9 +96,11 @@ class QNode(object):
         """Combine this node with another node into a QCombination
         object.
         """
+        # If the other Q() is empty, ignore it and just use `self`.
         if getattr(other, "empty", True):
             return self
 
+        # Or if this Q is empty, ignore it and just use `other`.
         if self.empty:
             return other
 
@@ -146,6 +148,13 @@ class QCombination(QNode):
     def empty(self):
         return not bool(self.children)
 
+    def __eq__(self, other):
+        return (
+            self.__class__ == other.__class__
+            and self.operation == other.operation
+            and self.children == other.children
+        )
+
 
 class Q(QNode):
     """A simple query object, used in a query tree to build up more complex
@@ -164,3 +173,6 @@ class Q(QNode):
     @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

@@ -374,6 +374,38 @@ class TestQ(unittest.TestCase):
             == 2
         )
 
+    def test_equality(self):
+        assert Q(name="John") == Q(name="John")
+        assert Q() == Q()
+
+    def test_inequality(self):
+        assert Q(name="John") != Q(name="Ralph")
+
+    def test_operation_equality(self):
+        q1 = Q(name="John") | Q(title="Sir") & Q(surname="Paul")
+        q2 = Q(name="John") | Q(title="Sir") & Q(surname="Paul")
+        assert q1 == q2
+
+    def test_operation_inequality(self):
+        q1 = Q(name="John") | Q(title="Sir")
+        q2 = Q(title="Sir") | Q(name="John")
+        assert q1 != q2
+
+    def test_combine_and_empty(self):
+        q = Q(x=1)
+        assert q & Q() == q
+        assert Q() & q == q
+
+    def test_combine_and_both_empty(self):
+        assert Q() & Q() == Q()
+
+    def test_combine_or_empty(self):
+        q = Q(x=1)
+        assert q | Q() == q
+        assert Q() | q == q
+
+    def test_combine_or_both_empty(self):
+        assert Q() | Q() == Q()
 
 if __name__ == "__main__":
     unittest.main()