LINQ - if条件

Question

在代码中，被注释的部分是我需要解决的...是否有一种方法可以用LINQ编写这样的查询？我需要这个是因为我需要基于状态进行排序。

var result = (
     from contact in db.Contacts
     join user in db.Users on contact.CreatedByUserID equals user.UserID
     join deal in db.Deals on contact.ContactID equals deal.ContactID into deals
     orderby contact.ContactID descending
     select new ContactListView
     {
         ContactID = contact.ContactID,
         FirstName = contact.FirstName,
         LastName = contact.LastName,
         Email = contact.Email,
         Deals = deals.Count(),
         EstValue = deals.Sum(e => e.EstValue),
         SalesAgent = user.FirstName + " " + user.LastName,
         Tasks = 7,
         // This is critical part
         if(Deals == 0) Status = "Prospect";
         else
             Status = "Client";
         // End of critical part...
     })
     .OrderBy(filterQuery.OrderBy + " " + filterQuery.OrderType)
     .Where(filterQuery.Status);

- ilija veselica

Answer 1

Status = (deals.Count() == 0 ? "Prospect" : "Client")

这里使用了 "条件运算符"

条件运算符 (?:) 根据布尔表达式的值返回两个值中的一个。

编辑： 您可以像这样进行组合：

Status = (deals.Count() == 0 ? "Prospect" : (deals.Count() == 1 ? "Client" : "Other"))

在这种情况下，您经常使用deals.Count()，因此可以使用LINQ的let语法将结果存储在临时变量中：

var result = (
   from contact in db.Contacts
   join user in db.Users on contact.CreatedByUserID equals user.UserID
   join deal in db.Deals on contact.ContactID equals deal.ContactID into deals
   let dealCount = deals.Count()
   ... // Continue here
     Status = (dealCount == 0 ? "Prospect" : (dealCount == 1 ? "Client" : "Other"))

- GvS

---

除了必须使用deals.Count()而不是Deal之外，没有其他要求。如果有超过两种情况怎么办？是否有可能做到这一点？谢谢！ - ilija veselica

@ile - 当然可以，你只需要使用一些括号.. Status = (Deals.Count() == 0 ? "没有交易" : (Deals.Count() == 1 ? "一个交易" : "多个交易")) - Eric Johansson

Answer 2

// This is critical part
Status = deals.Any() ? "Client" : "Prospect"
// End of critical part...

- LukeH

Answer 3

ar result = (
     from contact in db.Contacts
     join user in db.Users on contact.CreatedByUserID equals user.UserID
     join deal in db.Deals on contact.ContactID equals deal.ContactID into deals
     orderby contact.ContactID descending
     select new ContactListView
     {
         ContactID = contact.ContactID,
         FirstName = contact.FirstName,
         LastName = contact.LastName,
         Email = contact.Email,
         Deals = deals.Count(),
         EstValue = deals.Sum(e => e.EstValue),
         SalesAgent = user.FirstName + " " + user.LastName,
         Tasks = 7,
         // This is critical part
         Status = deals.Count()==0 ? "Prospect" : "Client",
         // End of critical part...
     })
     .OrderBy(filterQuery.OrderBy + " " + filterQuery.OrderType)
     .Where(filterQuery.Status);

- Cheng Chen

---

deals.Any()会更好 :) - leppie