1 files changed, 22 insertions, 5 deletions
diff --git a/src/mongo/s/commands/cluster_commands_helpers.cpp b/src/mongo/s/commands/cluster_commands_helpers.cpp
index 50e170fec57..6fe459226eb 100644
--- a/src/mongo/s/commands/cluster_commands_helpers.cpp
+++ b/src/mongo/s/commands/cluster_commands_helpers.cpp
@@ -70,6 +70,12 @@ void appendWriteConcernErrorToCmdResponse(const ShardId& shardId,
 
 namespace {
 
+BSONObj appendDbVersion(BSONObj cmdObj, DatabaseVersion version) {
+    BSONObjBuilder cmdWithVersionBob(std::move(cmdObj));
+    cmdWithVersionBob.append("databaseVersion", version.toBSON());
+    return cmdWithVersionBob.obj();
+}
+
 std::vector<AsyncRequestsSender::Request> buildUnversionedRequestsForAllShards(
     OperationContext* opCtx, const BSONObj& cmdObj) {
     std::vector<AsyncRequestsSender::Request> requests;
@@ -98,11 +104,22 @@ std::vector<AsyncRequestsSender::Request> buildVersionedRequestsForTargetedShard
         }
     } else {
         // The collection is unsharded. Target only the primary shard for the database.
-        // Don't append shard version info when contacting the config servers.
-        requests.emplace_back(routingInfo.primaryId(),
-                              !routingInfo.primary()->isConfig()
-                                  ? appendShardVersion(cmdObj, ChunkVersion::UNSHARDED())
-                                  : cmdObj);
+
+        // Attach shardVersion "UNSHARDED", unless targeting the config server.
+        const auto cmdObjWithShardVersion = (routingInfo.db().primaryId() != "config")
+            ? appendShardVersion(cmdObj, ChunkVersion::UNSHARDED())
+            : cmdObj;
+
+        // Attach the databaseVersion if we have one cached for the database.
+        // TODO: After 4.0 is released, require the routingInfo to have a databaseVersion for all
+        // databases besides "config" and "admin" (whose primary shard cannot be changed).
+        // (In v4.0, if the cluster is in fcv=3.6, we may not have a databaseVersion cached for any
+        // database).
+        const auto cmdObjWithShardVersionAndDbVersion = routingInfo.db().databaseVersion()
+            ? appendDbVersion(cmdObjWithShardVersion, *routingInfo.db().databaseVersion())
+            : cmdObjWithShardVersion;
+
+        requests.emplace_back(routingInfo.db().primaryId(), cmdObjWithShardVersionAndDbVersion);
     }
     return requests;
 }