Simple.Data + Impromptu-Interface interfaces

databasefactory.cs

static class DatabaseFactory
{
    public static IDatabase Create()
    {
        Database.UseMockAdapter(CreateMockAdapter());

        // This single line of code applies all these interfaces
        return Impromptu.ActLike<IDatabase>(Database.Open());
    }

    private static InMemoryAdapter CreateMockAdapter()
    {
        var inmem = new InMemoryAdapter(StringComparer.OrdinalIgnoreCase);
        inmem.SetAutoIncrementKeyColumn("Customers", "Id");
        inmem.SetAutoIncrementKeyColumn("Employees", "Id");
        inmem.Join.Master("Customers", "Id", "Employees").Detail("Employees", "EmployerId", "Employer");
        return inmem;
    }
}

interfaces.cs

public interface IDatabase
{
    ICustomers Customers { get; }
    IEmployees Employees { get; }
}

public interface ICustomers
{
    ICustomer Get(int id);
    [UseNamedArgument]
    ICustomer Insert(string name = null, string location = null);
}

public interface IEmployees
{
    [UseNamedArgument]
    IEmployee Insert(string name = null, int employerId = 0);
}

public interface ICustomer
{
    int Id { get; set; }
    string Name { get; set; }
    string Location { get; set; }
    IList<IEmployee> Employees { get; } 
}

public interface IEmployee
{
    int Id { get; set; }
    int EmployerId { get; set; }
    ICustomer Employer { get; }
    string Name { get; set; }
}

tests.cs

[TestFixture]
public class CustomerTest
{
    [Test]
    public void TestInsert()
    {
        var db = DatabaseFactory.Create();
        var customer = db.Customers.Insert(name: "Megadodo", location: "Ursa Minor Beta");
        Assert.AreEqual(1, customer.Id);
        Assert.AreEqual("Megadodo", customer.Name);
        Assert.AreEqual("Ursa Minor Beta", customer.Location);
    }
    
    [Test]
    public void TestGet()
    {
        var db = DatabaseFactory.Create();
        db.Customers.Insert(name: "Megadodo", location: "Ursa Minor Beta");

        var customer = db.Customers.Get(1);

        Assert.AreEqual(1, customer.Id);
        Assert.AreEqual("Megadodo", customer.Name);
        Assert.AreEqual("Ursa Minor Beta", customer.Location);
    }

    [Test]
    public void TestLazyLoadDetail()
    {
        var db = DatabaseFactory.Create();
        var customer = db.Customers.Insert(name: "Megadodo", location: "Ursa Minor Beta");
        db.Employees.Insert(name: "Ford Prefect", employerId: customer.Id);
        db.Employees.Insert(name: "Zarniwoop", employerId: customer.Id);

        customer = db.Customers.Get(customer.Id);
        Assert.AreEqual(2, customer.Employees.Count);
        
        // Make sure we get the same list every time we access the property
        customer.Employees.RemoveAt(0);
        Assert.AreEqual(1, customer.Employees.Count);
    }

    [Test]
    public void TestLazyLoadMaster()
    {
        var db = DatabaseFactory.Create();
        var customer = db.Customers.Insert(name: "Megadodo", location: "Ursa Minor Beta");
        var employee = db.Employees.Insert(name: "Ford Prefect", employerId: customer.Id);
        Assert.AreEqual("Megadodo", employee.Employer.Name);
    }
}