feat(order): support call Order once to order by multi fields

chainable_api.go

@@ -219,6 +219,12 @@ func (db *DB) Order(value interface{}) (tx *DB) {
 		tx.Statement.AddClause(clause.OrderBy{
 			Columns: []clause.OrderByColumn{v},
 		})
+
+	case clause.OrderByColumns:
+		tx.Statement.AddClause(clause.OrderBy{
+			Columns: v,
+		})
+
 	case string:
 		if v != "" {
 			tx.Statement.AddClause(clause.OrderBy{

clause/order_by.go

@@ -6,6 +6,8 @@ type OrderByColumn struct {
 	Reorder bool
 }
 
+type OrderByColumns = []OrderByColumn
+
 type OrderBy struct {
 	Columns    []OrderByColumn
 	Expression Expression