PYTHON-1479 - Don't add projection to "find" cmd twice, 2

Author: ajdavis

pymongo/message.py

@@ -299,15 +299,11 @@ def get_message(self, set_slave_ok, sock_info, use_cmd=False):
 
         ns = _UJOIN % (self.db, self.coll)
         spec = self.spec
-        if sock_info.is_mongos:
-            spec = _maybe_add_read_preference(spec, self.read_preference)
 
         if use_cmd:
             ns = _UJOIN % (self.db, "$cmd")
             spec = self.as_command(sock_info)[0]
             ntoreturn = -1  # All DB commands return 1 document
-            return query(flags, ns, self.ntoskip, ntoreturn,
-                         spec, None, self.codec_options)
         else:
             # OP_QUERY treats ntoreturn of -1 and 1 the same, return
             # one document and close the cursor. We have to use 2 for
@@ -318,8 +314,13 @@ def get_message(self, set_slave_ok, sock_info, use_cmd=False):
                     ntoreturn = min(self.limit, ntoreturn)
                 else:
                     ntoreturn = self.limit
-            return query(flags, ns, self.ntoskip, ntoreturn,
-                         spec, self.fields, self.codec_options)
+
+        if sock_info.is_mongos:
+            spec = _maybe_add_read_preference(spec,
+                                              self.read_preference)
+
+        return query(flags, ns, self.ntoskip, ntoreturn,
+                     spec, None if use_cmd else self.fields, self.codec_options)
 
 
 class _GetMore(object):