Question

I am using ASP.NET MVC3 and EF 4.1
I have two DropDownList in my Model, It is required and not duplicated too.
And I want the Remote validate function: ValidateDuplicateInsert get firing when user submit data. But I can NOT get the ValidateDuplicateInsert function firing.
Where am I wrong?

My Model

    [Key]
    public int CMAndOrgID { get; set; }

    [Display(Name = "CM")]
    [Required(ErrorMessage = "CM is required.")]
    [Remote("ValidateDuplicateInsert", "CMAndOrg", HttpMethod = "Post", AdditionalFields = "CMID, OrganizationID", ErrorMessage = "CM is assigned to this Organization.")]
    public int? CMID { get; set; }

    [Display(Name = "Organization")]
    [Required(ErrorMessage = "Organization is required.")]
    public int? OrganizationID { get; set; }

    public virtual CM CM { get; set; }
    public virtual Organization Organization { get; set; }

The ValidateDuplicateInsert function in my CMAndOrg controller

    [HttpPost]
    public ActionResult ValidateDuplicateInsert(string cmID, string orgID)
    {
        bool flagResult = true;
        foreach (CMAndOrg item in db.CMAndOrgs)
        {
            if (item.CMID.ToString() == cmID && item.OrganizationID.ToString() == orgID)
            {
                flagResult = false;
                break;
            }
        }
        return Json(flagResult);
    }

And my View

@using (Html.BeginForm()) {
@Html.ValidationSummary(true)
<fieldset>
    <legend>CMAndOrg</legend>

    <div class="editor-label">
        @Html.LabelFor(model => model.CMID, "CM")
    </div>
    <div class="editor-field">
        @Html.DropDownList("CMID", String.Empty)
        @Html.ValidationMessageFor(model => model.CMID)
    </div>

    <div class="editor-label">
        @Html.LabelFor(model => model.OrganizationID, "Organization")
    </div>
    <div class="editor-field">
        @Html.DropDownList("OrganizationID", String.Empty)
        @Html.ValidationMessageFor(model => model.OrganizationID)
    </div>

    <p>
        <input type="submit" value="Create" />
    </p>
</fieldset>
}

Answer 1

There is a bug in MVC3 related to unobtrusive validation on dropdownlist. Please reference to this http://aspnet.codeplex.com/workitem/7629%5B^] link for more detail explaination.

Briefly, you can’t use the same name for category collection and category field, so just change your collection name and update following line in your view

@Html.DropDownList("CategoryID", String.Empty)

with this

@Html.DropDownListFor(model => model.CategoryID, new SelectList((System.Collections.IEnumerable)ViewData["Categories"], "Value", "Text"))

Thanks again Henry He

Original link
http://www.codeproject.com/Articles/249452/ASP-NET-MVC3-Validation-Basic?msg=4330725#xx4330725xx