Support converting varchar to nvarchar for mssql database (#24105) (#24168)

Backport #24105 by @lunny

In #12269, all string fields of struct will generate a NVARCHAR column
in database, but for those Gitea instances installed before that PR,
users have to convert columns themselves.

In this PR, we update the `./gitea admin convert` commands to support
both MySQL and MSSQL database converting. Previously, it only supported
converting `utf8 -> utf8mb4` for MySQL.
Now, it will check the database types.
If it's MSSQL, it will convert `VARCHAR -> NVARCHAR` as well.

Co-authored-by: Lunny Xiao <xiaolunwen@gmail.com>

cmd/convert.go

@@ -17,7 +17,7 @@ import (
 var CmdConvert = cli.Command{
 	Name:        "convert",
 	Usage:       "Convert the database",
-	Description: "A command to convert an existing MySQL database from utf8 to utf8mb4",
+	Description: "A command to convert an existing MySQL database from utf8 to utf8mb4 or MSSQL database from varchar to nvarchar",
 	Action:      runConvert,
 }
 
@@ -35,17 +35,22 @@ func runConvert(ctx *cli.Context) error {
 	log.Info("Log path: %s", setting.Log.RootPath)
 	log.Info("Configuration file: %s", setting.CustomConf)
 
-	if !setting.Database.Type.IsMySQL() {
-		fmt.Println("This command can only be used with a MySQL database")
-		return nil
-	}
-
+	switch {
+	case setting.Database.Type.IsMySQL():
 		if err := db.ConvertUtf8ToUtf8mb4(); err != nil {
 			log.Fatal("Failed to convert database from utf8 to utf8mb4: %v", err)
 			return err
 		}
-
 		fmt.Println("Converted successfully, please confirm your database's character set is now utf8mb4")
+	case setting.Database.Type.IsMSSQL():
+		if err := db.ConvertVarcharToNVarchar(); err != nil {
+			log.Fatal("Failed to convert database from varchar to nvarchar: %v", err)
+			return err
+		}
+		fmt.Println("Converted successfully, please confirm your database's all columns character is NVARCHAR now")
+	default:
+		fmt.Println("This command can only be used with a MySQL or MSSQL database")
+	}
 
 	return nil
 }

models/db/convert.go

@@ -42,6 +42,33 @@ func ConvertUtf8ToUtf8mb4() error {
 	return nil
 }
 
+// ConvertVarcharToNVarchar converts database and tables from varchar to nvarchar if it's mssql
+func ConvertVarcharToNVarchar() error {
+	if x.Dialect().URI().DBType != schemas.MSSQL {
+		return nil
+	}
+
+	sess := x.NewSession()
+	defer sess.Close()
+	res, err := sess.QuerySliceString(`SELECT 'ALTER TABLE ' + OBJECT_NAME(SC.object_id) + ' MODIFY SC.name NVARCHAR(' + CONVERT(VARCHAR(5),SC.max_length) + ')'
+FROM SYS.columns SC
+JOIN SYS.types ST
+ON SC.system_type_id = ST.system_type_id
+AND SC.user_type_id = ST.user_type_id
+WHERE ST.name ='varchar'`)
+	if err != nil {
+		return err
+	}
+	for _, row := range res {
+		if len(row) == 1 {
+			if _, err = sess.Exec(row[0]); err != nil {
+				return err
+			}
+		}
+	}
+	return err
+}
+
 // Cell2Int64 converts a xorm.Cell type to int64,
 // and handles possible irregular cases.
 func Cell2Int64(val xorm.Cell) int64 {