PYTHON-1527 - Fix default writeConcern override

pymongo/bulk.py

@@ -263,7 +263,7 @@ class _Bulk(object):
         while run:
             cmd = SON([(_COMMANDS[run.op_type], self.collection.name),
                        ('ordered', self.ordered)])
-            if write_concern.document:
+            if not write_concern.is_server_default:
                 cmd['writeConcern'] = write_concern.document
             if self.bypass_doc_val and sock_info.max_wire_version >= 4:
                 cmd['bypassDocumentValidation'] = True

pymongo/collection.py

@@ -2078,7 +2078,7 @@ class Collection(common.BaseObject):
                     kwargs["cursor"]["batchSize"] = first_batch_size
 
             if (sock_info.max_wire_version >= 5 and dollar_out and
-                    self.write_concern):
+                    not self.write_concern.is_server_default):
                 cmd['writeConcern'] = self.write_concern.document
 
             cmd.update(kwargs)
@@ -2403,7 +2403,8 @@ class Collection(common.BaseObject):
         cmd = SON([("renameCollection", self.__full_name), ("to", new_name)])
         with self._socket_for_writes() as sock_info:
             with self.__database.client._tmp_session(session) as s:
-                if sock_info.max_wire_version >= 5 and self.write_concern:
+                if (sock_info.max_wire_version >= 5 and
+                        not self.write_concern.is_server_default):
                     cmd['writeConcern'] = self.write_concern.document
                 cmd.update(kwargs)
                 return sock_info.command(
@@ -2530,7 +2531,8 @@ class Collection(common.BaseObject):
         inline = 'inline' in cmd['out']
         sock_ctx, read_pref = self._socket_for_primary_reads(session)
         with sock_ctx as (sock_info, slave_ok):
-            if (sock_info.max_wire_version >= 5 and self.write_concern and
+            if (sock_info.max_wire_version >= 5 and
+                    not self.write_concern.is_server_default and
                     not inline):
                 cmd['writeConcern'] = self.write_concern.document
             cmd.update(kwargs)

pymongo/database.py

@@ -412,7 +412,9 @@ class Database(common.BaseObject):
         if isinstance(command, string_type):
             command = SON([(command, value)])
 
-        if sock_info.max_wire_version >= 5 and write_concern:
+        if (sock_info.max_wire_version >= 5 and
+                write_concern and
+                not write_concern.is_server_default):
             command['writeConcern'] = write_concern.document
 
         command.update(kwargs)

pymongo/pool.py

@@ -535,7 +535,9 @@ class SocketInfo(object):
                 collation is None):
             raise ConfigurationError(
                 'Collation is unsupported for unacknowledged writes.')
-        if self.max_wire_version >= 5 and write_concern:
+        if (self.max_wire_version >= 5 and
+                write_concern and
+                not write_concern.is_server_default):
             spec['writeConcern'] = write_concern.document
         elif self.max_wire_version < 5 and collation is not None:
             raise ConfigurationError(

pymongo/write_concern.py

@@ -46,7 +46,7 @@ class WriteConcern(object):
           journal. Cannot be used in combination with `j`.
     """
 
-    __slots__ = ("__document", "__acknowledged")
+    __slots__ = ("__document", "__acknowledged", "__server_default")
 
     def __init__(self, w=None, wtimeout=None, j=None, fsync=None):
         self.__document = {}
@@ -84,6 +84,13 @@ class WriteConcern(object):
                 raise TypeError("w must be an integer or string")
             self.__document["w"] = w
 
+        self.__server_default = not self.__document
+
+    @property
+    def is_server_default(self):
+        """Does this WriteConcern match the server default."""
+        return self.__server_default
+
     @property
     def document(self):
         """The document representation of this write concern.
@@ -110,8 +117,3 @@ class WriteConcern(object):
 
     def __ne__(self, other):
         return self.__document != other.document
-
-    def __bool__(self):
-        return bool(self.__document)
-
-    __nonzero__ = __bool__  # Python 2.

test/test_common.py

@@ -155,6 +155,10 @@ class TestCommon(IntegrationTest):
         wc = WriteConcern(w=2, wtimeout=1000)
         self.assertEqual(wc, c.write_concern)
 
+        # Can we override back to the server default?
+        db = c.get_database('pymongo_test', write_concern=WriteConcern())
+        self.assertEqual(db.write_concern, WriteConcern())
+
         db = c.pymongo_test
         self.assertEqual(wc, db.write_concern)
         coll = db.test

test/test_read_write_concern_spec.py

@@ -232,7 +232,7 @@ def create_document_test(test_case):
                 self.assertEqual(
                     concern.acknowledged, test_case['isAcknowledged'])
                 self.assertEqual(
-                    not bool(concern), test_case['isServerDefault'])
+                    concern.is_server_default, test_case['isServerDefault'])
         if 'readConcern' in test_case:
             # Any string for 'level' is equaly valid
             concern = ReadConcern(**test_case['readConcern'])