add tag on_update

dialects/dialect.go

@@ -280,5 +280,14 @@ func ColumnString(dialect Dialect, col *schemas.Column, includePrimaryKey bool)
 		}
 	}
 
+	if col.IsOnUpdate {
+		if _, err := bd.WriteString("ON UPDATE CURRENT_TIMESTAMP"); err != nil {
+			return "", err
+		}
+		if err := bd.WriteByte(' '); err != nil {
+			return "", err
+		}
+	}
+
 	return bd.String(), nil
 }

dialects/mysql.go

@@ -414,7 +414,9 @@ func (db *mysql) GetColumns(queryer core.Queryer, ctx context.Context, tableName
 		if extra == "auto_increment" {
 			col.IsAutoIncrement = true
 		}
-
+		if strings.Contains(extra, "ON UPDATE CURRENT_TIMESTAMP") {
+			col.IsOnUpdate = true
+		}
 		if !col.DefaultIsEmpty {
 			if !alreadyQuoted && col.SQLType.IsText() {
 				col.Default = "'" + col.Default + "'"

schemas/column.go

@@ -30,6 +30,7 @@ type Column struct {
 	Length2         int
 	Nullable        bool
 	Default         string
+	IsOnUpdate      bool
 	Indexes         map[string]int
 	IsPrimaryKey    bool
 	IsAutoIncrement bool

session_schema.go

@@ -296,6 +296,7 @@ func (session *Session) Sync2(beans ...interface{}) error {
 			for _, col2 := range oriTable.Columns() {
 				if strings.EqualFold(col.Name, col2.Name) {
 					oriCol = col2
+					oriCol.IsOnUpdate = col.IsOnUpdate
 					break
 				}
 			}

tags/tag.go

@@ -76,6 +76,7 @@ var (
 		"CACHE":     CacheTagHandler,
 		"NOCACHE":   NoCacheTagHandler,
 		"COMMENT":   CommentTagHandler,
+		"ON_UPDATE": OnUpdateTagHandler,
 	}
 )
 
@@ -215,6 +216,12 @@ func UniqueTagHandler(ctx *Context) error {
 	return nil
 }
 
+// OnUpdateTagHandler
+func OnUpdateTagHandler(ctx *Context) error {
+	ctx.col.IsOnUpdate = true
+	return nil
+}
+
 // CommentTagHandler add comment to column
 func CommentTagHandler(ctx *Context) error {
 	if len(ctx.params) > 0 {