L2sAR.cs

public class Customer {
  public int Id { get; set; } //assumes public property named  "Id" is PK
  public string Name { get; set; } //all public read/write properties auto-mapped to db cols
}

//config:
ActiveRecordConfiguration.Configure(cfg => {
   cfg.ConnectToSqlServer("(local)", "mydb", "user", "pass");
   cfg.MapTypesFromAssemblyContaining<Customer>();
   //lots of other options...
});

//usage:
using(ContextScope.Begin()) { //in a web app, this can be transparent using a scope per request
  var customer = new Customer { Name = "Jeremy" };
  customer.Save();
} //changes committed on scope disposal

using(ContextScope.Begin()) {
  var cust = Customer.FindById(1); //normal AR-style operations
}

//testability:
var fakeData = new[] { new Customer { Id = 1 }, new Customer { Id = 2 } };
using(Customer.Fake(fakeData)) { //replaces underlying data access with in-memory collection
  var cust = Customer.FindById(1); 
}