CODEWITHSUNDEEP
c#asp.net-mvcdictionarymodel-binding
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Reputation: 540

MVC 6 Modelbinding complex dictionaries

I'm trying to post a form containing a dictionary of complex types. The dictionary looks like this: 

 public Dictionary<Question, List<QuestionAlternative>> Questions { get; set; }

One question can have many alternatives.

The question itself looks like this: 

public class Question
{
    public Guid Id { get; set; }

    public string Text { get; set; }

    public Guid TestId { get; set; }

    public Test Test { get; set; }

    public ICollection<QuestionAlternative> QuestionAlternatives { get; set; }

    public Guid? QuestionTypeId { get; set; }
    public QuestionType QuestionType { get; set; }
}

And then there's the QuestionAlternative: 

public class QuestionAlternative
{
    public Guid Id { get; set; }

    public string Alternative { get; set; }

    public Guid QuestionId { get; set; }

    public Question Question { get; set; }
}

My form looks like this: 

  <form asp-controller="Answer" asp-action="AnswerMe" method="post">
        @foreach (var questionPair in Model.Questions)
        {
            @Html.Hidden("Questions[" + questionIndex + "].Key.Id", questionPair.Key.Id)
            <br />
            foreach (var alternative in questionPair.Value)
            {
              <label for="@alternative.Id">@questionPair.Key.Text</label>
              <textarea id="@alternative.Id" name="@("Questions["+ questionIndex + "].Value["+ index +"]")"></textarea>

               index++;
             }
            }
            questionIndex++;
        }
        <input type="submit" class="button" value="Answer" />
    </form>

The ActionResult that i'm posting to looks like this: 

  [AllowAnonymous]
  [HttpPost("AnswerMe")]
  public IActionResult AnswerMe([FromBody]AnswerViewModel model)
  {
    foreach(var item in model.Questions) //throws exception 
    ....
  }

and my viewmodel:

public class AnswerViewModel
{
    public ODELDAL.Entities.Test Test { get; set; }

    public Dictionary<Question, List<QuestionAlternative>> Questions { get; set; }

    public Guid SelectedRole { get; set; }
}

When I post my form the dictionary named Questions is null.

Is it possible to achieve this with the default modelbinder or do i need to build a custom one.

If so, how would that solution look like?

Thanks in advance

Upvotes: 1

Views: 447

Answers (1)

Nkosi
Nkosi

Reputation: 247018

Since a Question already possesses a collection of QuestionAlternative why not use a simple collect (List, array....etc) in your view model...

public class AnswerViewModel {
    public ODELDAL.Entities.Test Test { get; set; }    
    public Question[] Questions { get; set; }    
    public Guid SelectedRole { get; set; }
}

...and an updated view...

<form asp-controller="Answer" asp-action="AnswerMe" method="post">
    @for(int i = 0; i < Model.Questions.Length; i++) {
        @Html.HiddenFor(m => m.Questions[i].Id)
        <br />
        for(int j = 0; j < m.Questions[i].QuestionAlternatives.Count; j++) {
            @Html.LabelFor(m => m.Questions[i].QuestionAlternatives[j].Alternative,m.Questions[i].QuestionAlternatives[j].Text)
            @Html.TextAreaFor(m => m.Questions[i].QuestionAlternatives[j].Alternative)
        }
    }

    <input type="submit" class="button" value="Answer" />
</form>

The model binder will have an easier task of reconstructing your model using this approach as it will be able to use the expressions to generate the ids for the html tags.

For example, the hidden input will look something like this when generated

<input data-val="true" id="Questions_0__Id" name="Questions[0].Id" value="{Some-Guid-Value_Here}" type="hidden">

Upvotes: 1

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