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

    public string Name { get; set; }
}

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

    public string Name { get; set; }
}

public class MyDatabase : Database
{
    public MyDatabase()
    {
        var peopleTable = base.Tables.Create<Person, int>(p => p.Id);
        var groupTable = base.Tables.Create<Group, int>(g => g.Id);

        var peopleGroupIdIndex = peopleTable.CreateIndex(
            new RedBlackTreeIndexFactory<Person>(), 
            p => p.GroupId);

        this.Tables.CreateRelation(
            groupTable.PrimaryKeyIndex, 
            peopleGroupIdIndex, 
            x => x, 
            x => x);

        this.People = peopleTable;
        this.Groups = groupTable;
    }

    public ITable<Person> People { get; private set; }

    public ITable<Group> Groups { get; private set; }
}

MyDatabase db = new MyDatabase();

db.Groups.Insert(new Group { 
    Id = 1, 
    Name = "Alpha Group" });

db.Groups.Insert(new Group { 
    Id = 2, 
    Name = "Beta Group" });

db.People.Insert(new Person { 
    Id = 1, 
    Name = "John Doe", 
    GroupId = 1, 
    BirthDay = new DateTime(1966, 4, 12) });

var query =
    from p in db.People
    join g in db.Groups on p.GroupId equals g.Id
    select new { Name = p.Name, Group = g.Name };
    
query.ToList()

var q = db.Groups.Where(x => x.Name.StartsWith("B"));

// Update command
q.Update(x => new Group { Name = x.Name + " (taged)" });

// Delete command
q.Delete();