Fix readpreference option parsing in MongoDB transport (#751)

* Fix readpreference option parsing in MongoDB transport

* Update changelog

1 files changed, 5 insertions, 2 deletions

diff --git a/kombu/transport/mongodb.py b/kombu/transport/mongodb.py
index 2a7f8ff3..75372ab0 100644
--- a/kombu/transport/mongodb.py
+++ b/kombu/transport/mongodb.py
@@ -274,18 +274,21 @@ class Channel(virtual.Channel):
                                  if self.connect_timeout else None),
         }
         options.update(parsed['options'])
+        options = self._prepare_client_options(options)
 
         return hostname, dbname, options
 
     def _prepare_client_options(self, options):
         if pymongo.version_tuple >= (3,):
             options.pop('auto_start_request', None)
+            if isinstance(options.get('readpreference'), int):
+                modes = pymongo.read_preferences._MONGOS_MODES
+                options['readpreference'] = modes[options['readpreference']]
         return options
 
     def _open(self, scheme='mongodb://'):
-        hostname, dbname, options = self._parse_uri(scheme=scheme)
+        hostname, dbname, conf = self._parse_uri(scheme=scheme)
 
-        conf = self._prepare_client_options(options)
         conf['host'] = hostname
 
         env = _detect_environment()