サンプル
[RegularExpression(@"\d{4}/(0[1-9]|1[0-2])", ErrorMessage = "日付ですよ")] [RegularExpression(@"\d{4}/\d{1,2}", ErrorMessage = "日付ですよ")]
[RegularExpression(@"\d{4}/(0[1-9]|1[0-2])", ErrorMessage = "日付ですよ")] [RegularExpression(@"\d{4}/\d{1,2}", ErrorMessage = "日付ですよ")]