diff --git a/db/db.go b/db/db.go
index babe641..ec47f7f 100644
--- a/db/db.go
+++ b/db/db.go
@@ -698,34 +698,25 @@ type txFunc func(tx *sql.Tx) error
 
 // withTx wraps a function in an sql transaction. the transaction is committed if there's no error, or rolled back if there is one.
 // if dbOrTx is an sql.DB, a new transaction is started
-func withTx(dbOrTx interface{}, f txFunc) (err error) {
-	var tx *sql.Tx
-
-	switch t := dbOrTx.(type) {
-	case *sql.Tx:
-		tx = t
-	case *sql.DB:
-		tx, err = t.Begin()
-		if err != nil {
-			return err
-		}
-		defer func() {
-			if p := recover(); p != nil {
-				if rollBackError := tx.Rollback(); rollBackError != nil {
-					log.Error("failed to rollback tx on panic - ", rollBackError)
-				}
-				panic(p)
-			} else if err != nil {
-				if rollBackError := tx.Rollback(); rollBackError != nil {
-					log.Error("failed to rollback tx on panic - ", rollBackError)
-				}
-			} else {
-				err = errors.Err(tx.Commit())
-			}
-		}()
-	default:
-		return errors.Err("db or tx required")
+func (s *SQL) withTx(f txFunc) (err error) {
+	tx, err := s.conn.Begin()
+	if err != nil {
+		return err
 	}
+	defer func() {
+		if p := recover(); p != nil {
+			if rollBackError := tx.Rollback(); rollBackError != nil {
+				log.Error("failed to rollback tx on panic - ", rollBackError)
+			}
+			panic(p)
+		} else if err != nil {
+			if rollBackError := tx.Rollback(); rollBackError != nil {
+				log.Error("failed to rollback tx on panic - ", rollBackError)
+			}
+		} else {
+			err = errors.Err(tx.Commit())
+		}
+	}()
 
 	return f(tx)
 }