问如何防止保存重复数据？

EN

    @model IEnumerable<PaymentAdviceEntity.Role>
    <div id="roleList">
    <div class="span6">
    <div class="span12 HeaderField2">
        Roles
    <legend style="margin-bottom:2px;margin-top:5px;"></legend>
    </div>

    <div  class="span12">    




        <div style="display:inline-block"></div>
        <div id="addrole" style="display:none">
        <span> @Html.TextBox("RoleName", String.Empty, new { @id = "RoleName",style="margin-bottom:0px;" })</span>

           <span> 
               <input type="button" value="Save" id="btnSave"/>
                <input type="button"  value="Cancel" id="btnCancel" />
           </span>
      </div>    
        <div style="margin-top:5px;">
 <span id="RoleNameValidation" style="display:none;color:Red;">Role already exists</span>
        </div>

    </div>
    </div>

 $("#RoleName").blur(function ()
    {
        var Role_Name = $('#RoleName').val();
        //alert(RoleName);
        var url = "@Html.Raw(Url.Action("checkForUniqueName","Role",new {@RName = "RoleName"}))";
        url = url.replace("RoleName", Role_Name);
        $.post(url, function (data)
        {
            if (data == false) {

                $("#RoleNameValidation").show();
                $('#RoleName').focus();
            }
            else {
                $("#RoleNameValidation").hide()
            }
        });
    });

 public ActionResult checkForUniqueName(string RName)
         {
            bool Valid = false;

            var RoleList = from e in db.Roles
                           where e.Name.Equals(RName)
                           select e;
            if (RoleList.Count() > 0 )  
            {
                Valid = false;
            }
            else
            {
                Valid = true;
            }

            return Json(Valid, JsonRequestBehavior.AllowGet);


         }