asp.net mvc Remote远程验证

/// <summary>
/// 课程编号
/// </summary>
[MaxLength(50)]
[Remote("IsUnique_Available", "Course")]
[Required(ErrorMessageResourceName = "Course_CourseNum", ErrorMessageResourceType = typeof(ErrorMessage))]
public string CourseNum { get; set; }

#region 验证课程编号不唯一
public JsonResult IsUnique_Available(string CourseNum)
{
Course model = o_Res.GetCourseAny(a => a.CourseNum == CourseNum);
if (model == null)
{
return Json(true, JsonRequestBehavior.AllowGet);
}
else
{
string suggestedUID = String.Format(CultureInfo.InvariantCulture, "课程编号:{0} 已经存在！", CourseNum);
return Json(suggestedUID, JsonRequestBehavior.AllowGet);
}
}
#endregion

<td colspan="3">
@Html.TextBoxFor(a => a.CourseNum, new { maxlength = 50 }) @Html.ValidationMessageFor(model => model.CourseNum)
</td>

<td colspan="3">
@Html.TextBoxFor(a => a.CourseNum, new { maxlength = 50 , disabled = true }) @Html.ValidationMessageFor(model => model.CourseNum)
</td>