g := gen.NewGenerator(gen.Config{
    Mode:              gen.WithoutContext,
    ModelPkgPath:      modelsPath,
    FieldWithIndexTag: true,
    FieldWithTypeTag:  true,
})
// ....
g.GenerateModelAs(table, db.Config.NamingStrategy.SchemaName(table), gen.FieldGORMTag("created_at", "->"))

type User struct {
    CreatedAt    time.Time `gorm:"->" json:"created_at"`  // created time
}

type User struct {
    CreatedAt    time.Time `gorm:"->;column:created_at;type:datetime(3);not null;default:CURRENT_TIMESTAMP(3)" json:"created_at"`  // created time
}

// 定义
func FieldGORMTagHandler(func(columnName, gormTag string) string) model.FilterFieldOpt

// 使用
gen.FieldGORMTagHandler(func(columnName, gormTag string) string {
    if (columnName == "created_at") {
        return "->;" + gormTag
    }

    return gormTag
})

// 定义
func FieldGORMTagHandler(func(gormTag string) string, columnNames ...string) model.FilterFieldOpt

// 使用
gen.FieldGORMTagHandler(func(gormTag string) string {
    return "->;" + gormTag
}, "created_at", "updated_at")

gen.FieldGORMTag("created_at", func(tag field.GormTag) field.GormTag {//处理gorm tag
				tag.Set("<-", "false") //加只读 tag
				tag.Set("serialize","json")
				//tag.Remove("type")     //移除gorm的 type tag
				return tag
			}),