Question

I’m debating with myself about the best practice approach to controlling an Aggreate View Model class that I’ve created for my app… Let’s say I have an aggregate model that has a PurchaseOrder object and a list of line items that belong to that Purchase Order, and a few other auxuliary/related objects. This view model is just a wrapper around all these objects that you would typcially need when working on any give PurchaseOrder.

After after creating an instance of this view model, I then want it to load up a PurchaseOrder (and it will load the PurchaseOrderLineItems automatically and saturate all the other related objects)…

So, to instruct the view model to load up a PurchaseOrder, is it more acceptable to:

1. Instruct the view model by setting a property on it (and let the property setter of the view model class respond by loading up the data)

   ViewModel.PoNo = 1234;

or

2. Call a method on the view model to do the work:

   ViewModel.LoadPurchaseOrder(1234);

Just to give a few mode detials about the Aggregate View Model, it basically looks like this:

    public class ViewModel
    {
      //-- private fields
      PurchaseOrder _Po = new PurcaseOrder();
      List<PurchaseOrderItem> _PoLineItems;
      Vendor _Vend = new Vendor();
      int _PoNo;
    
      //-- public properties here
    
      ViewModel(){} // Constructor

    }

Answer 1

Does this ViewModel serve any purpose other than relating all the PurchaseOrder informaton together? If not i would say you should pass your purchase order in the constructor of ViewModel because it seems like ViewModel would only be in a valid state if it had a PurchaseOrder.

EDIT: Given the 2 options you have listed, I think a method call makes more sense than setting a property as it is easier to tell that you are loading a PurchaseOrder into this ViewModel. As a developer, I wouldn’t think that setting an integer property would end up loading all kinds of objects on the ViewModel, but one might expect that from calling a method.