ASP.NET MVC NHibernate - Bind Multiple Favorite Lists to IList <T>

Question

How to associate a multi select combo box with a list attribute of a manually added staging table?

Classes

public class Department { public virtual int Id { get; set; } public virtual IList<Lam> Lams { get; set; } } public class Person { public virtual int Id { get; set; } public virtual IList<Lam> Lams { get; set; } } public class Lam { public virtual int Id { get; set; } public virtual Department Department { get; set; } public virtual Person Person { get; set; } } 

ViewModel

 public class DepartmentCreateEditViewModel { public Department Department { get; set; } public IList<Person> Persons { get; set; } } 

Actionresult

  public ActionResult Create() { // Get all Persons var persons = repositoryPerson.GetAll(); // Create ViewModel var viewModel = new DepartmentCreateEditViewModel() { Department = new Department(), Persons = persons }; // Display View return View(viewModel); } 

Create view

I tried to add a listbox like this.

 @Html.ListBoxFor(model => model.Department.Lams, new SelectList(Model.Persons, "Id", "Name"), new { @class = "form-controll" }) 

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To save an object, I want to return a department object

 [HttpPost] public ActionResult Create(Department department) 

Linking to a drop-down list (with people) in IList does not work. How am I supposed to do this? Is it possible?

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[Change] Code after Eric's suggestion

Create ActionResult

 [HttpPost] public ActionResult Create(DepartmentCreateEditViewModel viewModelPostBack) 

View

 @Html.ListBoxFor(model => model.Department.Lams, new MultiSelectList(Model.Persons, "Id", "Name"), new { @class = "form-controll" }) 

What will I be back:

 viewModelPostBack {EmpLaceMgmt.ViewModels.DepartmentCreateEditViewModel} Department: {EmpLaceMgmt.Models.Department} Persons: null viewModelPostBack.Department {EmpLaceMgmt.Models.Department} Id: 0 Lams: Count = 0 

The generated HTML is as follows

 <select class="form-controll" id="Department_Lams" multiple="multiple" name="Department.Lams"> <option value="1">Example Person</option> </select> 

Answer 1

You have three problems. Firstly, you are trying to bind to IList<T> , but this will not work, because the model’s middleware will not know which specific object it should create to satisfy this ... There are many objects that support IList<T> , so which one?

Secondly, you need to use a MultiSelectList , not a SelectList in your helper.

Third, you submit a different type of model than you use to create your pages. And this type has a completely different structure. In the structure with which you create your page, your data is created with the name Department.Lams (because Department is a property of your ViewModel), but your Post action uses the Department model, which would be a binder to look for an object simply called Lams , not Department.Lams .

So, convert your models to a specific type, such as List<Lam> , and then go back to your ViewModel, not the department, and extract the department from ViewModel and finally replace the helper with this:

 @Html.ListBoxFor(model => model.Department.Lams, new MultiSelectList(Model.Persons, "Id", "Name"), new { @class = "form-controll" })