linq 中的右外连接到实体查询

Question

每个 Order 需要 RoutingStep 秒，每个步骤包含一个 Operation，每个操作需要 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;}
}

我想编写一个 linq to entity 查询（方法语法）来了解每个订单通过哪些 Workshops 而没有通过哪些 Workshops。换句话说如果我总共有 4 个 Workshop 并且 O1 包含 3 个 Routing 步骤，我想要 O1 的以下结果：

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

我写了下面的代码

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

我应该使用哪个代码代替“???” ？

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"
        });

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