Linq-to-Sql: Build an Order-OrderItems query i.e. a Master-Detail Graph

Question

Given the following classes:

class Order
{
    public int Id;
    public string OrderNumber;
    public DateTime OrderDate;
}

class OrderItem
{
    public int Id;
    public int OrderId;
    public string ProductName;
    public decimal Price;
}

class OrderComment
{
    public int Id;
    public int OrderId;
    public string Subject;
    public string Message;
}

and the following DataContext

public interface IDataContext
{
    IQueryable<Order> Orders{get;}
    IQueryable<OrderItem> OrderItems{get;}
    IQueryable<OrderComment> OrderComments{get;}
}

How would you go about building a Linq query that will create an Order graph with its details (items & comments) as shown below:

class OrderDetails
{
    public int Id;
    public string OrderNumber;
    public DateTime OrderDate;

    public IList<OrderItem> Items;
    public IList<OrderComment> Comments;

}

Note: We want to hit the database only once.