MM-32525 Incorrect number of mentions for channels when threads are enabled (#16853)

store/sqlstore/thread_store.go

@@ -108,6 +108,35 @@ func (s *SqlThreadStore) Get(id string) (*model.Thread, error) {
 	return &thread, nil
 }
 
+func (s *SqlThreadStore) GetThreadMentionsForUserPerChannel(userId, teamId string) (map[string]int64, error) {
+	type Count struct {
+		UnreadMentions int64
+		ChannelId      string
+	}
+	var counts []Count
+
+	sql, args, _ := s.getQueryBuilder().
+		Select("SUM(UnreadMentions) as UnreadMentions", "ChannelId").
+		From("ThreadMemberships").
+		LeftJoin("Threads ON Threads.PostId = ThreadMemberships.PostId").
+		LeftJoin("Channels ON Threads.ChannelId = Channels.Id").
+		Where(sq.And{
+			sq.Or{sq.Eq{"Channels.TeamId": teamId}, sq.Eq{"Channels.TeamId": ""}},
+			sq.Eq{"ThreadMemberships.UserId": userId},
+			sq.Eq{"ThreadMemberships.Following": true},
+		}).
+		GroupBy("Threads.ChannelId").ToSql()
+
+	if _, err := s.GetMaster().Select(&counts, sql, args...); err != nil {
+		return nil, err
+	}
+	result := map[string]int64{}
+	for _, count := range counts {
+		result[count.ChannelId] = count.UnreadMentions
+	}
+	return result, nil
+}
+
 func (s *SqlThreadStore) GetThreadsForUser(userId, teamId string, opts model.GetUserThreadsOpts) (*model.Threads, error) {
 	type JoinedThread struct {
 		PostId         string