MVC4 Best Practice Database Models v View Models (passed to view)

Question

I want to get into good habits from the start so I have this question and a problem:

I have been doing the following which has been working, then I read this post

Here

This example of what I have been doing:

CONTROLLER

public ActionResult OneDollar130(Int32 number)
{
    MyEDM db = new MyEDM();
    MyDBModel model = db.MyTable.Where(t => t.Current == 1 && t.No == number).First();
    return View(model);
}

VIEW

@model MyProject.MyDBModel
<table>
  <tr>
    @if (Model.fldNo1 == "")
    {
        <td class="numberTD">
            @Html.ActionLink("1", "Number1", "Number", new { model = Model, number = 1 }, null)
        </td>
    }
    else
    {
        <td class="numberTD2">
            @Html.ActionLink("1", "Number2", "Number", new { model = Model, number = 1 })
        </td>
     }
  </tr>
</table>

I am using the model from my EDM and passing it to the View.

I read in above post that I should not pass my database models to the view as this is bad practice. This concerns me somewhat as I want to be doing it right.

So based on the above post I change my code to experiment and hit a snag:

CONTROLLER

public ActionResult OneDollar112(Int32 TableNo)
{
    return View(new getOneDollar112Game(TableNo));
}

MODEL

public class getMyModel
{
    MyEDM db = new MyEDM();
    public MyDBModel MyModel { get; set; }

    public getMyModel() { }
    public getMyModel(Int32 number)
    {
        MyModel = db.MyTable
            .Where(t => t.Current == 1 && t.No == numbner).First();
    }
}

VIEW

@model MyProject.Models.getMyModel
<table>
  <tr>
    @if (Model.fldNo1 == "")
    {
        <td class="numberTD">
            @Html.ActionLink("1", "Number1", "Number", new { model = Model, number = 1 }, null)
        </td>
    }
    else
    {
        <td class="numberTD2">
            @Html.ActionLink("1", "Number2", "Number", new { model = Model, number = 1 })
        </td>
    }
  </tr>
</table>

Okay so my 2 questions are:

1. Which is the best practice ... does what I was doing before break the rule of not passing DB models to the view?

2. If the second method is correct (which I am supposing) why do I continually get the error that fldNo1 does not exist?

eg: CS1061: 'MyProject.Models.getMyModel' does not contain a definition for 'fldNo1' and no extension method 'fldNo1' accepting a first argument of type 'MyProject.Models.getMyModel' could be found (are you missing a using directive or an assembly reference?)

Answer 1

I am also not fond of using database objects as models.

What I do, is rely on the MVC structure in my project.

Views - contains views

Models - contains the models, dedicated for the view

Controllers - contain the controller, also responsible for making the translation between database and view models.

In my controllers I add repositories (see Repository Pattern ) to communicate with the database. If I would like to show a user in my view I'd end up with something like this

public ActionResult Show()
{
    // entity model
    var user = _userRepository.GetUserByName(User.Identity.Name);

    // translate to view model
    var model = new User
    {
        Name = user.Name,
        EmailAddress = user.EmailAddress
    }
    // Send the view model to the view
    return View(model);
}

Does that help?

Answer 2

You should have separate Models and ViewModels for at least two reasons:

1. Security

The default model binder in MVC will bind with any matching post data fields to Model properties. This provides a security whole that can be exploited if you have properties that are not meant to be updated, but are in the Model (eg fake a post back with the property names that are not normally displayed)

By using a ViewModel and explicitly passing each required property from ViewModel to the actual Model you defend against this attack vector

2. Complexity

Most reasonable applications will require a multitude of models and model collections per view

eg a basic CRM customer view might have: customer details, but not scores, list of names and phone numbers, summary list of recent transactions, list of products registered etc. These might exist in a complex collection of objects, with names and phone numbers in different models, recent transactions might be order number, total number of order lines, and only first three SKU codes etc.

A ViewModel allows you to build up just the parts and summaries needed for display from the Models and static data caches. The result should simplify the workflow to build a view, and make it much more testable

There is normally a path of inheritance from simple ViewModels to the final complex ViewModel actually used

Answer 3

1) I edited your code.

Action:

public ActionResult OneDollar112(Int32 tableNo)
{
    return View(new OneDollar112ViewModel(tableNo));
}

Model:

public class OneDollar112ViewModel
{
    private static MyEDM db = new MyEDM();
    private MyDBModel myModel;

    public string fldNo1 
    {
        get 
        { 
            return myModel == null
                ? myModel.fldNo1
                : null;
        }

        set 
        {
            // Your set logic here 
        }
    }    

    public OneDollar112ViewModel(Int32 number)
    {
        myModel = db.MyTable
            .Where(t => t.Current == 1 && t.No == numbner).SingleOrDefault();
    }
}    

View:

@model MyProject.Models.OneDollar112ViewModel
<table>
    <tr>
    @if (Model.fldNo1 == "")
    {
        <td class="numberTD">
            @Html.ActionLink("1", "Number1", "Number", new { model = Model, number = 1 }, null)
        </td>
    }
    else
    {
        <td class="numberTD2">
            @Html.ActionLink("1", "Number2", "Number", new { model = Model, number = 1 })
        </td>
    }
    </tr>
</table>

2) You should use view models to separate your business logic from your data layer which you could encapsulate in services and in the future take advantage of dependency injection.