Understanding model use in view

Question

Consider the following code snippet

public class FirstViewModel
{
    public IEnumerable<SelectListItem> GetSomeData()
    {
      //query dbcontext here
    }
}

public class SecondViewModel
{
    public Employee Employee { get; set; }
    public Stock Stock { get; set; }
    //more properties
}

So with the first snippet I can do the following in my code:

@Html.DropDownListFor(model => Model.Employee, new App.Models.ViewModels.FirstViewModel().GetSomeData(), "Please choose something")

In the second snippet I can do:

@Html.DropDownListFor(model => Model.Employee, new SelectList(Model.Employee), "Select Status")

What I'm trying to achieve is to have multiple models in one view for my MVC app. My question is would it be better to have a separate view model for each or one big view model which reference all other models. I'm very new to MVC so any help would be appreciated.

Answer 1

Each of my Views has a ViewModel - that may be an aggregate of two VMs (as properties). Important to remember the VM is a Model for the View - its not a Data Model in its own right. The data model should be elsewhere and the Controller maps between the two.

(I've never had a ViewModel actively pull data from a DB before - I've always had the Controller populate the ViewModel. Not directly related to your question, but important to go in the right direction from the start.)

Answer 2

I would base it on use. If you need all of the data all of the time why not include it all.

Other things to consider:

1. Do you need all of the data all the time?
2. Are there maximums to worry about for reads?
3. Possible memory limitations?
4. Number of visits/traffic load considerations.