MVC Not Parsing the Correct Value from Model

Question

Can anyone tell me why, if my model clearly shows my values to be "true" or "false" MVC still thinks it says, "true,false." I assume this is because it is confusing the Request with my Model; however, I am explicitly telling it to use the Model.

As you can see in the image above, the model value is "true." However, in the image below, it thinks the value is "true,false." How can I make it just use "true?"

Model

public class TagCategorySearchViewModel
{
    public long Id { get; set; }

    public string Name { get; set; }

    public List<TagSearchViewModel> Tags { get; set; }
}

public class TagSearchViewModel
{
    public long Id { get; set; }

    public string Name { get; set; }

    public bool IsSelected { get; set; }
}

Controller

    [Authorize]
    public ActionResult FilterPrereqGrid(EditStudentPrerequisitesViewModel model, int page = 1)
    {
        model.Prerequisites = new List<PrerequisiteListViewModel>();
        var businessPartner = _bpManager.GetBusinessPartnerByMapGuid(model.BusinessPartnerMapGuid);

        model.Prerequisites.AddRange(_epManager.GetFullPrerequisitesLeftJoinedWithExperience(model.ExperienceId, businessPartner?.Id));

        // fix for how MVC binds checkboxes... it send "true,false" instead of just true, so we need to just get the true
        for (int i = 0; i < model.TagCategories?.Count(); i++)
        {
            for (int j = 0; j < model.TagCategories[i].Tags?.Count(); j++)
            {
                model.TagCategories[i].Tags[j].IsSelected = bool.Parse((Request.QueryString[$"TagCategories[{i}].Tags[{j}].IsSelected"] ?? "false").Split(',')[0]);
            }
        }

        var selectedTagIds = model.TagCategories?.SelectMany(x => x.Tags).Where(x => x.IsSelected == true).Select(x => x.Id).ToArray();

        // filter by selected tags
        if (selectedTagIds.Any())
        {
            model.Prerequisites = (from p in model.Prerequisites
                                   let prereqTagIds = p.Prerequisite.PrerequisiteTags.Select(et => et.TagId)
                                   where selectedTagIds.All(x => prereqTagIds.Contains(x))
                                   select p).ToList();
        }

        model.Prerequisites = (from m in model.Prerequisites
                               let ownerDocs = _deManager.GetDocumentsByOwnerAndSourceId(model.BusinessPartnerMapGuid, m.Prerequisite.Id).OrderByDescending(e => e.CreatedDate)
                               select new PrerequisiteListViewModel
                               {
                                   Prerequisite = m.Prerequisite,
                                   Selected = m.Selected,
                                   Mandatory = m.Mandatory,
                                   HasExpiration = m.Prerequisite.HasExpiration,
                                   BusinessExpirationPeriod = m.Prerequisite.ExpirationPeriod == 0 ? "None" : m.Prerequisite.ExpirationPeriod.ToString(),
                                   DocOwnerGuid = (ownerDocs.Any() ? model.BusinessPartnerMapGuid : Guid.Empty),
                                   DocRowGuid = (ownerDocs.Any() ? ownerDocs.First().DocRowguid : Guid.Empty),
                                   HasDocuments = ownerDocs.Any()
                               }).ToList();

        int rowsPerPage = 1;

        model.TotalRecords = model.Prerequisites.Count();
        model.Prerequisites = model.Prerequisites.Skip(page * rowsPerPage - rowsPerPage).Take(rowsPerPage).ToList();

        return PartialView("~/Views/BusinessExperience/_EditPrerequisites.cshtml", model);
    }

Please can you share code for the model and controller.

user1023602
– user1023602

2017-03-17 15:10:08 +00:00
Commented Mar 17, 2017 at 15:10 — user1023602
– user1023602, Commented Mar 17, 2017 at 15:10
@buffjape Added. Thanks.

user1477388
– user1477388

2017-03-17 15:13:12 +00:00
Commented Mar 17, 2017 at 15:13 — user1477388
– user1477388, Commented Mar 17, 2017 at 15:13

Brian Mains · Accepted Answer · 2017-03-17 15:21:03Z

2

That is by design. The Html.CheckBoxFor extension actually renders something like the following:

<input type="checkbox" .. />
<input type="hidden" />

So both of these have the same name as the property you are rendering out. When checked, the checkbox returns "True", but when unchecked, the checkbox returns nothing. That is the way checkboxes work with form posts. In order to determine that nothing was checked, the MVC framework included a hidden field so that it would return "False" when not checked, but "True,False" when checked (since multiple items with the same name return this way from the form post). And then MVC model binding converts "True,False" to true.

You could just render your own <input type="checkbox" /> with a value of true, and that would just return true, but when unchecked, nothing gets rendered. Be aware of that...

answered Mar 17, 2017 at 15:21

Brian Mains

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3 Comments

user1477388 Over a year ago

I considered that, but I am handling the way it sends, "true,false" in my action and am only ever returning the correct "true" or "false" value back to the view. I don't understand how it is still thinking that it says, "true,false" when it clearly does not as shown in the screenshot.

Brian Mains Over a year ago

"true,false' is what comes back through the HTTP post. The default model binder for booleans changes true,false to true when assigned to a bool property.

user1477388 Over a year ago

Gotcha; I ended up needing to switch to POST anyway since GET has a limit (there is a limit to how much data you can shove into a querystring). So, all worked out using the default model binder. Thanks.

user1477388 · Accepted Answer · 2017-03-17 19:15:09Z

This actually works, it's a shame I can't just do the obvious way and have to write this all out though!

@model List<Prep2PracticeWeb.Models.ViewModels.TagCategorySearchViewModel>

@if (Model != null)
{
    <div class="tag-categories">
        @for (int i = 0; i < Model.Count(); i++)
        {
            @Html.HiddenFor(x => Model[i].Id)
            @Html.HiddenFor(x => Model[i].Name)
            <h4 data-toggle="collapse" data-target="#CollapsableTagCategory_@Model[i].Id" aria-expanded="false" aria-controls="CollapsableTagCategory_@Model[i].Id">
                <span class="glyphicon glyphicon-chevron-right"></span>
                <span class="glyphicon glyphicon-chevron-down"></span>
                @Model[i].Name
            </h4>
                            <div id="CollapsableTagCategory_@Model[i].Id" class="tag-container collapse">
                                @if (Model[i].Tags != null)
                                {
                                    for (int j = 0; j < Model[i].Tags.Count(); j++)
                                    {
                                        @Html.HiddenFor(x => Model[i].Tags[j].Id)
                                        @Html.HiddenFor(x => Model[i].Tags[j].Name)
                                        @* the following commented out line won't work because MVC is funny *@
                                        @*<label>@Html.CheckBoxFor(x => Model[i].Tags[j].IsSelected) @Model[i].Tags[j].Name</label>*@
                                        <label>
                                            <input @(Model[i].Tags[j].IsSelected ? @"checked=""checked""" : string.Empty) data-val="true" data-val-required="The IsSelected field is required." id="TagCategories_@(i)__Tags_@(j)__IsSelected" name="TagCategories[@i].Tags[@j].IsSelected" type="checkbox" value="true"> @Model[i].Tags[j].Name
                                            <input name="TagCategories[@i].Tags[@j].IsSelected" type="hidden" value="false">
                                        </label>
                                    }
                                }
                            </div>
        }
    </div>
}

Update: I realized GET was not an appropriate strategy in this scenario given the fact that the querystring can only be so long before the server returns a 500 error. I switched to POST which alleviated the issue.

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