Question

I am teaching myself asp .net mvc3.

I have a partial view which uses various models and lookup type db. I want to keep it strongly typed and use it in multiple places but I am not sure how to implement it.
The example below should explain it better. This question might get a bit long and I appreciate your patience.

The partial view basically gives a small description of the property. A snippet of the ‘_PropertyExcerptPartial’ is below:

@model Test.ViewModels.PropertyExcerptViewModel

<div>
    <h3>@Html.DisplayFor(model => model.Property.NoOfBedrooms) bedroom @Html.DisplayFor(model => model.FurnitureType.FurnitureTypeDescription) flat to Rent </h3>
…
</div>

I want to keep this partial view strongly typed and use it in multiple places. The model that it is strongly typed to is as follows:

public class PropertyExcerptViewModel
{
    public Property Property { get; set; }
    public FurnitureType FurnitureType { get; set; }
}

The two 2 database that this model looks up is as follows:

 public class Property
 {
    public int PropertyId {get; set; }       
    ...
    public int NoOfBedrooms {get; set;}
    public int FurnishedType { get; set; }
    ...
 }

public class FurnishedType
{
    public int FurnishedTypeId { get; set; }
    public string FurnishedTypeDescription { get; set; }
}

The furnished type database is basically just a lookup table with the following data:
1 – Furnished
2 – Not Furnished
3 – Part Furnished
4 – Negotiable

I have many such lookups in that I only store an int value in the property database which can be used to look up the description. These databases are not linked to property database and the value of furniture type is read via a function GetFurnitureType(id). I pass stored int value of Property.FurnitureType as the id.

However, I encounter a problem when I try to use this partial view as I am not sure how to pass these multiple models from a view to partial view.

Say I am trying to create an ‘added property’ page. This page basically list the properties added by the logged in user. To facilitate this, I have created another function called GetAddedProperties(userId) that return the properties added by a particular user. In the ‘added property’ view, I can call a foreach function to loop through all the properties returned by GetAddedProperties and display the _PropertyExcerptPartial. Something like this:

<div>
    @foreach (var item in //Not sure what to pass here)
    {
        @Html.Partial("_PropertyExcerptPartial",item)
    }
</div>

However, I can’t use the partial view to display information as it will display the int value of furniture type stored in the property database and I am not sure how to get the corresponding FurnitureTypeDescription and pass it to the partial view from the ‘added property’ page.

Any help would be appreciated. Thanks a lot!

Answer 1

You should start by designing a real view model, not some class that you suffix its name with ViewModel and stuff your domain models inside. That’s not a view model.

So think of what information you need to work with in your view and design your real view model:

public class PropertyExcerptViewModel
{
    public int NoOfBedrooms  { get; set; }
    public string FurnishedTypeDescription { get; set; }
}

and then adapt your partial to work with this view model:

@model Test.ViewModels.PropertyExcerptViewModel
<div>
    <h3>
        @Html.DisplayFor(model => model.NoOfBedrooms) 
        bedroom 
        @Html.DisplayFor(model => model.FurnitureTypeDescription) 
        flat to Rent 
    </h3>
    ...
</div>

OK, now that we have a real view model let’s see how we could populate it. So basically the main view could be strongly typed to a collection of those view models:

@model IEnumerable<Test.ViewModels.PropertyExcerptViewModel>
<div>
    @foreach (var item in Model)
    {
        @Html.Partial("_PropertyExcerptPartial", item)
    }
</div>

and the last bit of course is the main controller that will do all the db querying and building of the view model that will be passed to the main view:

[Authorize]
public ActionResult SomeAction()
{
    // get the currently logged in username
    string user = User.Identity.Name;

    // query the database in order to fetch the corresponding domain entities
    IEnumerable<Property> properties = GetAddedProperties(user);

    // Now let's build the view model:
    IEnumerable<PropertyExcerptViewModel> vm = properties.Select(x => new PropertyExcerptViewModel
    {
        NoOfBedrooms = x.NoOfBedrooms,
        FurnishedTypeDescription = GetFurnitureType(x.FurnishedType).FurnishedTypeDescription
    });

    // and finally pass the view model to the view
    return View(vm);    
}

Be careful with the lazy nature of EF if that is the ORM that you are using in order not to fall into the SELECT N + 1 trap.