hiearchical data, catel, and MVVM - wpf

Question

I'm working with Catel, MVVM, WPF and am wondering about how to work with nested/hiearchical data.
Let's say from a database I've got a list of Customers, each with a list of Invoices, each with a list of InvoiceItems. Customers own many Invoices which own many InvoiceItems.
I've got a working solution, but I do not like it. My approach was to build a collection of classes that would act a kind of like an ado.net “dataset.” A class would represent each layer of the hiearchy.
This top level class, CustomerModel, would contain a collection of of InvoiceBlocks:
CustomerModel
ObservableCollection of < InvoicesBlocks >
Each InvoceBlock would contain an Invoice and a collection of InvoiceItems:
InvoiceBlock
Invoice
ObservableCollection of < InvoiceItems >
It seemed clever until wading through the databinding path= satements. There are also times when I have to loop through the sets mamaully to update totals, defeating a major selling point of MVVM.
So, I've decided to learn more about grouping with LINQ queries and databinding. Is this the way the pros do it?

Answer 1

What you can do is make each view model responsible for using the right services to retrieve the data.
Note that I did not use Catel properties to make it easy to understand, but you can simply use Catel.Fody or rewrite the properties to get Catel properties.
public class CustomerViewModel
{
private readonly IInvoiceService _invoiceService;
public CustomerViewModel(ICustomer customer, IInvoiceService invoiceService)
{
Argument.IsNotNull(() => customer);
Argument.IsNotNull(() => invoiceService);
Customer = customer;
_invoiceService = invoiceService;
}
public ICustomer Customer { get; private set; }
public ObservableCollection<IInvoice> Invoices { get; private set; }
protected override void Initialize()
{
var customerInvoices = _invoiceService.GetInvoicesForCustomer(Customer.Id);
Invoices = new ObservableCollection<IInvoice>(customerInvoices);
}
}
public class InvoiceViewModel
{
private readonly IInvoiceService _invoiceService;
public InvoiceViewModel(IIinvoice invoice, IInvoiceService invoiceService)
{
Argument.IsNotNull(() => invoice);
Argument.IsNotNull(() => invoiceService);
Invoice = invoice;
_invoiceService = invoiceService;
}
public IInvoice Invoice { get; private set; }
public ObservableCollection<IInvoiceBlock> InvoiceBlocks { get; private set; }
protected override void Initialize()
{
var invoiceBlocks = _invoiceService.GetInvoiceBlocksForInvoice(Invoice.Id);
InvoiceBlocks = new ObservableCollection<IInvoiceBlock>(invoiceBlocks);
}
}
Now you are fully in control what happens when.