从for循环返回局部视图

Question

My page allows the user to select businesses from a checkbox list and have those businesses inserted into the db.

I use a foreach to loop through each item in the form collection and then save through the db context.

All of this is working well.

public ActionResult RecordBusinesses(FormCollection collection)
    {
        foreach (var item in collection.GetValues("mycheckboxlist"))
        {
            modelentity modelentity = new modelentity();

            if (ModelState.IsValid)
            {
                db.modelentity.Add(modelentity);
                db.SaveChanges();
            }

            return PartialView("_mypartialview", modelentity);
        }
        return PartialView("_mypartialview");
    }

In the view, the checkbox list is wrapped in an ajax form.

@using (Ajax.BeginForm(
                        "RecordBusinesses",
                        new AjaxOptions
                        {
                        HttpMethod = "POST",
                        InsertionMode = InsertionMode.InsertBefore,
                        UpdateTargetId = "insertedbusiness"
                        }))
                        {

                            foreach(var b in Model)
        {
            <input type="checkbox" name="mycheckboxlist" value="@b.businessid">@b.name
        <br />
        }
                            </div>
                            <input type="submit" />
                        }

This form posts to the action and, again, everything is working well.

My problem is that only the first entry is posted back to the screen. So the partialview that is returned from the controller is added to the dom if there's only one business selected in the checkbox, but if there's multiple businesses selected, only the first one shows up.

I'm guessing thats because the controller method "returns" after the first successful insert, ending the process and subsequent calls are not made.

My only confusion there is that all of the businesses are successfully inserted. I would expect those to fail as well, but upon refreshing the page, all businesses are displayed correctly.

Answer 1

The issue here is your action

public ActionResult RecordBusinesses(FormCollection collection)
{
    foreach (var item in collection.GetValues("mycheckboxlist"))
    {
        ...
        return PartialView("_mypartialview", modelentity);
    }
    return PartialView("_mypartialview");
}

Once you return from the action the request ends, ASP.NET doesn't understand that you want to iterate through the rest of the loop. If it did, it would result in multiple calls to & from the server which you probably wouldn't want anyway.

Think about it, your code is the equivalent to

for(int i = 0; i <= 10; i++)
{
    Console.WriteLine(i);
    return i;
}

This would only ever output 0 . It looks like what you are really after here is the yield keyword

for (int i = 0; i <= 10; i++)
{
    yield return i;
}

Which I am pretty sure you can't do in ASP.NET in the context of an HTTP request.

The way around this is to do all your rendering server side. Change your action to actually pass your model back to some container view

public ActionResult RecordBusinesses(FormCollection collection)
{
    List<Entity> myEntities = ...;
    foreach (var item in collection.GetValues("mycheckboxlist"))
    {
        ...
        myEntities.Add(new ...);
    }
    return View("SomeContainerView", myEntities);
}

Then in your view, make the calls to render each partial

@model System.Collections.Generic.List<Entity>

@foreach (var entity in Model)
{
     @Html.RenderPartial("_mypartialview", entity)
}

Answer 2

You cannot return multiple partial views from one action, in the same sense as you cannot receive multiple HTTP responses for one HTTP request.

Consider changing your partial view to accept a collection of entities and render all of them in a loop.