Question

In EditPhoto.cshtml:

@model vg_music.Models.images
@{
    ViewBag.Title = "EditPhoto";
}
<h2>
    EditPhoto2</h2>
<script src="@Url.Content("~/Scripts/jquery.validate.min.js")" type="text/javascript"></script>
<script src="@Url.Content("~/Scripts/jquery.validate.unobtrusive.min.js")" type="text/javascript"></script>
@using (Ajax.BeginForm(new AjaxOptions{UpdateTargetId = "AjaxDiv"})) {
    @Html.ValidationSummary(true)
    <div id="AjaxDiv">
        @Html.Partial("EditPhotoForm")
    </div>
}
<div>
    @Html.ActionLink("Back to List", "Index")
</div> 

EditPhotoForm.cshtml:

    @model vg_music.Models.images
<fieldset>
            <legend>images</legend>
            @Html.HiddenFor(model => model.id)
            <div class="editor-label">
                @Html.LabelFor(model => model.title)
            </div>
            <div class="editor-field">
                @Html.EditorFor(model => model.title)
                @Html.ValidationMessageFor(model => model.title)
            </div>
            <div class="editor-label">
                @Html.LabelFor(model => model.comment)
            </div>
            <div class="editor-field">
                @Html.EditorFor(model => model.comment)
                @Html.ValidationMessageFor(model => model.comment)
            </div>
            <div class="editor-label">
                @Html.LabelFor(model => model.filename)
            </div>
            <div class="editor-field">
            <img src="@Url.Content("~/uploads/images/little/"+Model.filename)" alt="@Model.title"/><br />                
            </div>
            <p>
                <input type="submit" value="Сохранить" />
            </p>
        </fieldset> 

PhotosController.cs:
….

[HttpPost]
    public ActionResult EditPhoto(images obj)
    {
        if (ModelState.IsValid)
        {
            var db = new EditImagesModel();
            db.SaveImage(obj);
            if (Request.IsAjaxRequest()) //This does not work.
            {
                return PartialView("EditPhotoForm");
            }
            return RedirectToAction("EditPhotos");

        }
        return View();
    }

….

Why is not satisfied:

if (Request.IsAjaxRequest())
{
    return PartialView("EditPhotoForm");
}

Answer 1

Why is not satisfied:

Because you forgot to include:

<script src="@Url.Content("~/Scripts/jquery.unobtrusive-ajax.js")" type="text/javascript"></script>

in your EditPhoto.cshtml page. And because of this the Ajax.BeginForm helper doesn’t perform any AJAX request but a simple form POST.

Contrary to ASP.NET MVC 1.0 and 2.0 where Ajax.* helpers such as Ajax.ActionLink and Ajax.BeginForm were polluting your markup with javascript obtrusively, in ASP.NET MVC 3 they simply generate HTML5 data-* attributes on the corresponding DOM elements. This way markup and javascript is kept separate. And you need javascript to interpret those attributes. This javascript is located in the jquery.unobtrusive-ajax.js script which needs to be included.