Separating the data access layer

Now that we've had a look at providing a variety of functionality through our base classes and interfaces, let's investigate how we can provide the Separation of Concerns that is crucial when using the MVVM pattern. Once again, we turn to the humble interface to help us to achieve this. Let's view a simplified example:

using System; 
using CompanyName.ApplicationName.DataModels; 
 
namespace CompanyName.ApplicationName.Models.Interfaces 
{ 
  public interface IDataProvider 
  { 
    User GetUser(Guid id); 
 
    bool SaveUser(User user); 
  } 
} 

We start off with a very simple interface. Of course, real applications will have a great many more methods than this, but the principle is the same, regardless of the complexity of the interface. So here, we just have a GetUser and a SaveUser method that our DataProvider classes need to implement. Now, let's look at the ApplicationDataProvider class:

using System; 
using System.Data.Linq;...