PYTHON-808 Prevent use of Database and Collection in boolean expressions (#728)

doc/changelog.rst

@@ -134,8 +134,13 @@ decodes datetime as naive by default.
 - The ``hint`` option is now required when using ``min`` or ``max`` queries
   with :meth:`~pymongo.collection.Collection.find`.
 - ``name`` is now a required argument for the :class:`pymongo.driver_info.DriverInfo` class.
+- :class:`~pymongo.collection.Collection` and :class:`~pymongo.database.Database`
+  now raises an error upon evaluating as a Boolean, please use the
+  syntax ``if collection is not None:`` or ``if database is not None:`` as
+  opposed to
+  the previous syntax which was simply ``if collection:`` or ``if database:``.
+  You must now explicitly compare with None.
 
- d
 Notable improvements
 ....................
 

doc/migrate-to-pymongo4.rst

@@ -321,6 +321,19 @@ Can be changed to this::
 
 .. _'system.profile' collection: https://docs.mongodb.com/manual/reference/database-profiler/
 
+Database.__bool__ raises NotImplementedError
+............................................
+:class:`~pymongo.database.Database` now raises an error upon evaluating as a
+Boolean. Code like this::
+
+  if database:
+
+Can be changed to this::
+
+  if database is not None:
+
+You must now explicitly compare with None.
+
 Collection
 ----------
 
@@ -621,6 +634,19 @@ can be changed to this::
 
   cursor = coll.find({}, min={'x', min_value}, hint=[('x', ASCENDING)])
 
+Collection.__bool__ raises NotImplementedError
+..............................................
+:class:`~pymongo.collection.Collection` now raises an error upon evaluating
+as a Boolean. Code like this::
+
+  if collection:
+
+Can be changed to this::
+
+  if collection is not None:
+
+You must now explicitly compare with None.
+
 SONManipulator is removed
 -------------------------
 

pymongo/collection.py

@@ -289,6 +289,11 @@ class Collection(common.BaseObject):
     def __hash__(self):
         return hash((self.__database, self.__name))
 
+    def __bool__(self):
+        raise NotImplementedError("Collection objects do not implement truth "
+                                  "value testing or bool(). Please compare "
+                                  "with None instead: collection is not None")
+
     @property
     def full_name(self):
         """The full name of this :class:`Collection`.

pymongo/database.py

@@ -840,6 +840,11 @@ class Database(common.BaseObject):
 
     next = __next__
 
+    def __bool__(self):
+        raise NotImplementedError("Database objects do not implement truth "
+                                  "value testing or bool(). Please compare "
+                                  "with None instead: database is not None")
+
     def dereference(self, dbref, session=None, **kwargs):
         """Dereference a :class:`~bson.dbref.DBRef`, getting the
         document it points to.

test/test_collection.py

@@ -2265,6 +2265,10 @@ class TestCollection(IntegrationTest):
                  ('$dumb', 2),
                  ('filter', {'foo': 1})]).to_dict())
 
+    def test_bool(self):
+        with self.assertRaises(NotImplementedError):
+            bool(Collection(self.db, 'test'))
+
 
 if __name__ == "__main__":
     unittest.main()

test/test_database.py

@@ -687,6 +687,10 @@ class TestDatabaseAggregation(IntegrationTest):
             with self.admin.aggregate(self.pipeline) as _:
                 pass
 
+    def test_bool(self):
+        with self.assertRaises(NotImplementedError):
+            bool(Database(self.client, "test"))
+
 
 if __name__ == "__main__":
     unittest.main()