Listing the customers

The next thing we need to do is to get a list of customers to display in the UI. Our approach will be to create a data provider that will query the entity framework to get our entities, which we will use as our models. To accomplish this, follow these steps:

1. Add a project reference from Northwind.ViewModel to Northwind.Data.

2. Add a .NET reference to System.Data.Entity.

3. Add using statements for System.Collections.Generic, Northwind.Data, and System.Data.Objects to MainWindowViewModel.

4. Add the following code to MainWindowViewModel:

   private IList<Customer> _customers;
   
   public IList<Customer> Customers
   {
       get 
       {
           if (_customers == null)
           {
               GetCustomers();
           }
           return _customers; 
       }
   }
   
   private void GetCustomers()
   {
       _customers 
           = new NorthwindEntities()
               .Customers.ToList();
   }

5. Update Expander in MainWindow as shown in the following code:

   <Expander Padding="10"
             Margin="4"
             BorderBrush...