LINQ中的右外部聯接到實體查詢

Question

每個Order在某些RoutingStep ，每個步驟都包含一個Operation ，每個工序都在Workshop 。

public class Order
{
   public int Id {get; set;}
   public string OrderNumber {get; set;}
   public virtual collection<Routing> Routings{get; set;}
}
public class Routing
{
   public int Id {get; set;}
   public virtual Order Order {get; set;}
   public virtual Operation Operation{get; set;}
}
public class Operation
{
   public int Id {get; set;}
   public virtual Workshop Workshop{get; set;}
}
public class Workshop
{
   public int Id {get; set;}
   public string Title {get; set;}
}

我想對實體查詢（方法語法）編寫一個linq，以了解每個訂單傳遞了哪個Workshop而沒有傳遞哪個Workshop 。 換句話說，如果我總共有4個Workshop並且O1包含3個Routing步驟，那么我想要O1以下結果：

------------------------------
| Order  |  Workshop | status |
------------------------------
|   O1   |   W1      |  pass  |
------------------------------
|   O1   |   W2      |  pass  |
------------------------------
|   O1   |   W3      |not pass|
------------------------------
|   O1   |   W4      |  pass  |
-------------------------------

我寫下面的代碼

var query = db.Orders
    .SelectMany(order=> order.Routings
    .Select(g => new
    {
        Number = g.Order.OrderNumber,
        Workshop = g.Operation.Workshop.Title,
        Status = g.????
    }).ToList();

我應該改用哪個代碼“ ???” ？

Answer 1

var query = db.Orders
    .SelectMany(x => db.Workshops, (x, y) => new { Order = x, Workshop = y }) // all combinations of orders with workshops
    .GroupJoin( // left join to determine whether each combination actually exists
        db.Routings,
        x => x,  // proposed order-workshop pair
        y => new { Order = y.Order, Workshop = y.Operation.Workshop }, // existing order-workshop pair
        (x, ys) => new
        {
            x.Order.OrderNumber,
            x.Workshop.Title,
            Status = ys.Any() ? "pass" : "not pass"
        });