A simple project structure which separates business layer from the infrastructure layer and the application layer.

ProjectStructure.cs

/**
 * Solution
 * |- Domain
 * |  `- Customers
 * |     |- Customer.cs
 * |     `- ICustomersRepository.cs
 * |- Infrastructure
 * |  `- Customers
 * |     `- LinqToSqlCustomersRepository.cs
 * `- Application
 *    `- Program.cs
 *
 * Domain references nothing.
 * Infrastructure refences both Linq To Sql and Domain.
 * Application references both Domain and Infrastructure.
 *
 * LinqToSqlCustomersRepository.cs maps Customer against the Database and
 * implements the ICustomersRepository.cs interface.
 */

public class Customer
{
	public int Id { get; set; }

	public string Name { get; set; }
}

public interface ICustomersRepository
{
	IEnumerable<Customer> FindAll();
}

public class LinqToSqlCustomersRepository : ICustomersRepository
{
	public IEnumerable<Customer> FindAll()
	{
		using (var context = new MyDbContext())
		{
			var customers = context.Customers.OrderBy(x => x.Name)
				.Select(x => new Customer { Id = x.Id, x.Name });

			// NOTE: .ToList() is needed to force immediate execution since we
			// are disposing the context.
			return customers.ToList();
		}
	}
}

public class Program
{
	public static void Main()
	{
		var customersRepository = new LinqToSqlCustomersRepository();

		PrintAllCustomers(customersRepository);

		Console.WriteLine("Press Enter to exit...");
		Console.ReadLine();
	}

	private void PrintAllCustomers(ICustomersRepository customersRepository)
	{
		foreach (var customer in customersRepository.FindAll())
		{
			Console.WriteLine("{{ \"id\": \"{0}\", \"name\": \"{1}\" }}",
				customer.Id, customer.Name);
		}
	}
}