Proper way to populate a ViewModel?

Question

I'm working on a webapp for work, and I'm using standard CRUD style interactions. However, there are certain fields that I do not want the users updating, so I removed them from the view. However, if I don't explicitly set these fields, they're cleared when the model is updated in the database.

I'm concerned with what the proper method of populating the fields for my ViewModels is.

The rough idea I came up with was something like this:

My view model:

public class EditSoftwareTrackingViewModel 
{
    public EditSoftwareTrackingViewModel(SoftwareTracking model)
    {
        Id = model.Id;
        SoftwareId = model.SoftwareId;
        ComputerId = model.ComputerId;
        SoftwareActionId = model.SoftwareActionId;
        LastModified = model.LastModified;
        Computer = model.Computer;
        Software = model.Software;
        SoftwareAction = model.SoftwareAction;
    }
    public int Id { get; set; }
    [DisplayName("Software")]
    public int SoftwareId { get; set; }
    [DisplayName("Computer")]
    public int ComputerId { get; set; }
    [DisplayName("Software Action")]
    public int SoftwareActionId { get; set; }
    [DisplayName("Last Modified")]
    public DateTime? LastModified { get; set; }

    public virtual Computer Computer { get; set; }
    public virtual Software Software { get; set; }
    public virtual SoftwareAction SoftwareAction { get; set; }
}

My main model

[Table("asset.SoftwareTracking")]
public partial class SoftwareTracking
{
    public int Id { get; set; }
    [DisplayName("Software")]
    public int SoftwareId { get; set; }
    [DisplayName("Computer")]
    public int ComputerId { get; set; }
    [DisplayName("Date Entered")]
    public DateTime? EnteredDate { get; set; }
    [DisplayName("Software Action")]
    public int SoftwareActionId { get; set; }
    [DisplayName("Last Modified")]
    public DateTime? LastModified { get; set; }

    public virtual Computer Computer { get; set; }
    public virtual Software Software { get; set; }
    public virtual SoftwareAction SoftwareAction { get; set; }
}

And my controller using the view model

    public ActionResult Edit(int? id)
    {
        if (id == null)
        {
            return new HttpStatusCodeResult(HttpStatusCode.BadRequest);
        }
        EditSoftwareTrackingViewModel softwaretracking = new EditSoftwareTrackingViewModel(db.SoftwareTrackings.Find(id));
        if (softwaretracking == null)
        {
            return HttpNotFound();
        }
        GeneratePageData(softwaretracking.Software.Id);
        return View(softwaretracking);
    }

    [HttpPost]
    [ValidateAntiForgeryToken]
    public ActionResult Edit(EditSoftwareTrackingViewModel softwaretracking)
    {
        if (ModelState.IsValid)
        {
            softwaretracking.LastModified = DateTime.Now;
            var softwareTrack = db.SoftwareTrackings.Find(softwaretracking.Id);
            softwareTrack = new SoftwareTracking
            {
                Computer = softwaretracking.Computer,
                ComputerId = softwaretracking.ComputerId,
                LastModified = softwaretracking.LastModified,
                Software = softwaretracking.Software,
                SoftwareAction = softwaretracking.SoftwareAction,
                SoftwareActionId = softwaretracking.SoftwareActionId,
                SoftwareId = softwaretracking.SoftwareId,
                EnteredDate = softwareTrack.EnteredDate
            };

            db.Entry(softwareTrack).State = EntityState.Modified;
            db.SaveChanges();
            return RedirectToAction("Index");
        }
        GeneratePageData(softwaretracking.Software.Id);
        return View(softwaretracking);
    }

Is there a better alternative? Or should I continue to create my view models in this manner?

EDIT

My business logic and view

    private void GeneratePageData(int? id = null)
    {

        ViewBag.Computers = new SelectList(db.Computers, "Id", "ComputerName");
        ViewBag.SoftwareActions = new SelectList(db.SoftwareActions, "Id", "ActionPerformed");

        var usedSoft = (from softTrack in db.SoftwareTrackings
                        where (softTrack.SoftwareActionId != 3)
                        select softTrack.Software);

        var softwareList = (from soft in db.Softwares
                            where (
                                ((from softTrack in db.SoftwareTrackings
                                  where (softTrack.SoftwareActionId != 3 && softTrack.SoftwareId == soft.Id)
                                  select softTrack.Software).Count() < soft.KeyQuantity)
                                && !(soft.AssetStatusId == 4 || soft.AssetStatusId == 5)
                                || soft.Id == id)
                            select soft).ToList();

        ViewBag.SoftwareList = softwareList.Select(t => new SelectListItem
        {
            Text = t.SoftwareIdNameFull,
            Value = t.Id.ToString()
        });

    }

And my view

@model Lighthouse_Asset_Manager.Models.EditSoftwareTrackingViewModel

@{
    ViewBag.Title = "Edit Software Install";
    Layout = "";
}

<div class="modal-header">
    <button type="button" class="close" data-dismiss="modal" aria-hidden="true">
        &times;
    </button>
    <h4 class="modal-title" id="myModalLabel">Edit Software Install</h4>
</div>
<div class="modal-body">

    @using (Html.BeginForm(null, null, FormMethod.Post, new { id = "computerForm" }))
    {
        @Html.AntiForgeryToken()
        @Html.HiddenFor(model => model.Id)

        <div class="form-horizontal">
            @Html.ValidationSummary(true)


            <div class="form-group">
                @Html.LabelFor(model => model.SoftwareId, "Software", new { @class = "control-label col-md-2" })
                <div class="col-md-10">
                    @Html.DropDownList("SoftwareId", (IEnumerable<SelectListItem>)ViewBag.SoftwareList, "-- Select --", new
                    {
                        @style = "width:100%",
                        @class = "select2"
                    })
                    @Html.ValidationMessageFor(model => model.SoftwareId)
                </div>
            </div>

            <div class="form-group">
                @Html.LabelFor(model => model.ComputerId, "Computer", new { @class = "control-label col-md-2" })
                <div class="col-md-10">
                    @Html.DropDownList("ComputerId", (IEnumerable<SelectListItem>)ViewBag.Computers, "-- Select --", new
                    {
                        @style = "width:100%",
                        @class = "select2"
                    })
                    @Html.ValidationMessageFor(model => model.ComputerId)
                </div>
            </div>

            <div class="form-group">
                @Html.LabelFor(model => model.SoftwareActionId, "Action", new { @class = "control-label col-md-2" })
                <div class="col-md-10">
                    @Html.DropDownList("SoftwareActionId", (IEnumerable<SelectListItem>)ViewBag.SoftwareActions, "-- Select --", new
                    {
                        @style = "width:100%",
                        @class = "form-control"
                    })
                    @Html.ValidationMessageFor(model => model.SoftwareActionId)
                </div>
            </div>


            <div class="form-actions no-color">
                <button type="submit" class="btn btn-primary btn-sm"><i class="fa fa-floppy-o"></i> Edit Install Record</button>
                <button type="button" class="btn btn-default" data-dismiss="modal">
                    Cancel
                </button>
            </div>
        </div>
    }
</div>

Answer 1

You approach of using a view model is a good one. The answers to this question explains some of the benefits including preventing over-posting attacks, using view specific display and validation attributes and including view specific properties such as SelectLists. Tools such as automapper can make it easy to map between you data and view models and reduce the code in the controller. A few changes I would suggest to your view model. The LastModified, Computer, Software and SoftwareAction properties are not required (you not binding to these), and I would include the SelectList properties in the model rather than ViewBag

View model

public class EditSoftwareTrackingViewModel 
{
  public int Id { get; set; }
  [Display(Name="Software")]
  public int SoftwareId { get; set; }
  [Display(Name="Computer")]
  public int ComputerId { get; set; }
  [Display(Name="Software Action")]
  public int SoftwareActionId { get; set; }
  public SelectList Computers { get; set; }
  public SelectList SoftwareActions{ get; set; }
  public SelectList SoftwareList{ get; set; }
}

Then change the GeneratePageData() method to accept the view model

private void GeneratePageData(EditSoftwareTrackingViewModel model)
{
  model.Computers = new SelectList(db.Computers, "Id", "ComputerName");
  ....

and in the view (always preferable to use the strongly typed helpers)

@Html.DropDownListFor(m => m.SoftwareId, Model.SoftwareList, "-- Select --", new { @class = "select2" })

A few other things to note.

• You should use the [Display(Name="..")] attribute (not [DisplayName(..)])
• When you set the LastModified property, you should consider using UCT time.
• The hidden input for the Id property is not required in the view (assuming your using the default {controller}/{action}/{id} route mapping) - its added to the route values and will be bound anyway
• Unless you specifically want an id attribute for the form, you can just use @using(Html.BeginForm()) {
• You do not need the second parameter in LabelFor() - it can be just Html.LabelFor(m => m.SoftwareId, new { @class = "control-label col-md-2" }) since you have specified it in the [Display] attribute

Finally, if you want to simplify your view further, you could consider custom EditorTemplates or html helpers as indicated in this answer which would allow you to replace

<div class="form-group">
  @Html.LabelFor(model => model.SoftwareId, new { @class = "control-label col-md-2" })
  <div class="col-md-10">
    @Html.DropDownListFor(m => m.SoftwareId, Model.SoftwareList, "-- Select --", new { @class = "select2" })
    @Html.ValidationMessageFor(model => model.SoftwareId)
  </div>
</div>

with (custom EditorTemplate)

@Html.EditorFor(m => m.SoftwareId, "BootstrapSelect", Model.SoftwareList)

or (custom HtmlHelper)

@Html.BootstrapDropDownFor(m => m.SoftwareId, Model.SoftwareList)

Answer 2

You should use the AutoMapper to make the mapping between Model and ViewModel cleaner. Use this code to create the mapper first.

Mapper.CreateMap<SoftwareTracking, EditSoftwareTrackingViewModel>();
Mapper.CreateMap<EditSoftwareTrackingViewModel, SoftwareTracking>();

When you want to create a viewmodel from model, do this:

public ActionResult Edit(int? id)
{
    SoftwareTracking tracking = db.SoftwareTrackings.Find(id);
    EditSoftwareTrackingViewModel viewmodel = 
        Mapper.Map<SoftwareTracking, EditSoftwareTrackingViewModel>(tracking);
    return View(viewmodel);
}

When you want to populate the info from the viewmodel back to the model, do this

public ActionResult Edit(EditSoftwareTrackingViewModel vm)
{
    if (ModelState.IsValid)
    {
        vm.LastModified = DateTime.Now;
        var softwareTrack = db.SoftwareTrackings.Find(softwaretracking.Id);
        softwareTrack = 
           Mapper.Map<EditSoftwareTrackingViewModel, SoftwareTracking>(vm, softwareTrack);

        db.Entry(softwareTrack).State = EntityState.Modified;
        db.SaveChanges();
        return RedirectToAction("Index");
    }

Answer 3

To patch update your model without loading the object from Db. Try Attach:

    [HttpPost]
    [ValidateAntiForgeryToken]
    public ActionResult Edit(EditSoftwareTrackingViewModel softwaretracking)
    {
        if (ModelState.IsValid)
        {
            var softwareTrack = new SoftwareTracking
            {
                 Computer = softwaretracking.Computer,
                 ComputerId = softwaretracking.ComputerId,
                 LastModified = softwaretracking.LastModified,
                 Software = softwaretracking.Software,
                 SoftwareAction = softwaretracking.SoftwareAction,
                 SoftwareActionId = softwaretracking.SoftwareActionId,
                 SoftwareId = softwaretracking.SoftwareId,
                 EnteredDate = softwareTrack.EnteredDate
            };
            db.SoftwareTrackings.Attach(softwareTrack);

            db.Entry(softwareTrack).Property(a => a.Computer).IsModified = true;
            db.Entry(softwareTrack).Property(a => a.ComputerId).IsModified = true;
            db.Entry(softwareTrack).Property(a => a.LastModified).IsModified = true;
            db.Entry(softwareTrack).Property(a => a.Computer).IsModified = true;
            db.Entry(softwareTrack).Property(a => a.Software).IsModified = true;
            db.Entry(softwareTrack).Property(a => a.SoftwareAction).IsModified = true;

            db.Entry(softwareTrack).Property(a => a.SoftwareActionId).IsModified = true;
            db.Entry(softwareTrack).Property(a => a.SoftwareId).IsModified = true;
            db.SaveChanges();
            return RedirectToAction("Index");
        }
        GeneratePageData(softwaretracking.Software.Id);
        return View(softwaretracking);
    }

Regarding the second question about whether to use ViewModel or just use the Model directly. This is really a matter of opinion, each approach has its pros and cons. I don't have strong opinion about this, i just want to point out these pros and cons for your consideration:

• Using the model directly saves us from creating the viewModel, resulting in smaller source code and avoiding mapping logic but it would mix concerns. Because you use the same Model for your domain logic and for communcating with the client, any changes to the model may propagate up to the client if we don't take that into account.
• Using the viewModel is a good way for separation of concerns but it would require more effort and mapping logic (maybe slow down the performance a bit). To apply ViewModel efficiently, I suggest using a mapper: https://github.com/AutoMapper/AutoMapper/wiki/Getting-started

Answer 4

This is the Model Class

[Table("CURRENCY")]
    public class CurrencyClass : ICurrency
    {
        private Int32 mCURRENCY_ID = default(Int32);
        [Key]
        public virtual Int32 CURRENCY_ID  
        {
            get { return mCURRENCY_ID; }
            set { mCURRENCY_ID = value; }
        }
        private string mCURRENCY_NAME = default(string); 
        public virtual string CURRENCY_NAME 
        { 
            get { return mCURRENCY_NAME;}
            set { mCURRENCY_NAME = value;}
        }
        private string mCURRENCY_DESC = default(string);
        public  virtual string CURRENCY_DESC 
        {
            get { return mCURRENCY_DESC; }
            set { mCURRENCY_DESC = value; }
        }
        private string mCURRENCY_SYMBOLE = default(string);
        public virtual string CURRENCY_SYMBOLE 
        {
            get { return mCURRENCY_SYMBOLE; }
            set { mCURRENCY_SYMBOLE = value; }
        }
        private Int32 mcreated_by = default(Int32);
        public virtual Int32 created_by 
        {
            get { return mcreated_by; }
            set { mcreated_by = value; } 
        }
        private DateTime mcreated_date = default(DateTime);
        public virtual DateTime created_date 
        {
            get { return mcreated_date; }
            set { mcreated_date = value; } 
        }
        private Int32 mmodified_by = default(Int32);
        public virtual Int32 modified_by 
        {
            get { return mmodified_by; }
            set { mmodified_by = value; } 
        }
        private DateTime mmodified_date = default(DateTime);
        public virtual DateTime modified_date 
        {
            get { return mmodified_date; }
            set { mmodified_date = value; }
        }
    }

This is the ViewModel

public class CurrencyViewModel
    {
        [Key]
        public Int32 CURRENCY_Id { get; set; }
        [Required(ErrorMessage="Currency Name is required")]
        public string CURRENCY_NAME { get; set; }
        [Required(ErrorMessage="Currency Description is required")]
        public string CURRENCY_DESC { get; set; }
        [Required(ErrorMessage = "Currency Symbole is Required")]
        public string CURRENCY_SYMBOLE { get; set; }
    }

This is the Action

[HttpPost]
        [ActionName("Create")]
        public ActionResult Create(CurrencyViewModel vm)
        {
            if (!ModelState.IsValid)
            {
                return View("Create");
            }   

            obj.CURRENCY_NAME = vm.CURRENCY_NAME;
            obj.CURRENCY_DESC = vm.CURRENCY_DESC;
            obj.CURRENCY_SYMBOLE = vm.CURRENCY_SYMBOLE;
            obj.created_by = 1;
            obj.created_date = DateTime.Now;
            obj.modified_by = 1;
            obj.modified_date = DateTime.Now;
            db.Currencies.Add(obj);
            db.SaveChanges();

            return RedirectToAction("Index");
        }