使這一LINQ投影查詢更好

Question

假設我有這樣的定義域類：

public class MyDomainItem 
{ 
    public string PropertyA {get;set;} 
    public string PropertyB {get;set;} 
    public string ItemStatus {get;set;} 
    public ClassA ObjectA {get;set;} 
    public ClassB ObjectB {get;set;} 
} 

然後，我有一個LINQ查詢，看起來像這樣：根據我所知道的

var mylist = from a in someList 
       join b in someOtherList on a.Id equals b.Id 
       select new MyDomainItem 
       { 
        PropertyA = a.SomeProperty, 
        PropertyB = b.SomeOtherProperty, 
        ObjectA = a, 
        ObjectB = b 
       } 

，我可以解決ItemStatus有兩種方法：

foreach(var i in mylist) 
{ 
    if (i.ObjectA.YetAnotherProperty == "some criteria") 
    { 
     if (i.ObjectA.NestedObject.NestedProperty == "price is missing") 
     { 
      i.ItemStatus = "bad - category 1"; 
     } 
     else 
     { 
      i.ItemStatus = "bad - category 2"; 
     } 
    } 
    else 
    { 
     i.ItemStatus = "good"; 
    } 
} 

或調用功能，在LINQ QUER解決y：

var mylist = from a in someList 
       join b in someOtherList on a.Id equals b.Id 
       select new MyDomainItem 
       { 
        PropertyA = a.SomeProperty, 
        PropertyB = b.SomeOtherProperty, 
        ObjectA = a, 
        ObjectB = b, 
        ItemStatus = ResolveStatus(a) 
       } 

我腦海中有些東西只是不停地說，一定有更好的辦法。我真的很喜歡做的事情大致是這樣的：

var mylist = from a in someList 
       join b in someOtherList on a.Id equals b.Id 
       select new MyDomainItem 
       { 
        PropertyA = a.SomeProperty, 
        PropertyB = b.SomeOtherProperty, 
        ObjectA = a, 
        ObjectB = b, 
        ItemStatus =()=> 
        { 
         if (a.ObjectA.YetAnotherProperty == "some criteria") 
         { 
          if (a.ObjectA.NestedObject.NestedProperty == 
           "price is missing") 
          { 
           return "bad - category 1"; 
          } 
          else 
          { 
           return "bad - category 2"; 
          } 
         } 
         else 
         { 
          return "good"; 
         } 
        } 
       } 

是否有類似的東西，我可以做什麼？

在此先感謝... !!!

Answer 1

這樣的事情呢？

select new MyDomainItem 
{ 
    PropertyA = a.SomeProperty, 
    PropertyB = b.SomeOtherProperty, 
    ObjectA = a, 
    ObjectB = b, 
    ItemStatus = (a.YetAnotherProperty == "some criteria") 
        ? (a.NestedObject.NestedProperty == "price is missing" 
         ? "bad - category 1" 
         : "bad - category 2") 
        : "good"; 

雖然我會建議擴展ObjectA與屬性，爲您做這個評估，它在LINQ查詢看起來不太好。如果你沒有來源，你可以使用一個擴展方法

string GetItemStatus(this ObjectA item) { 
    if (item.YetAnotherProperty != "some criteria") { 
     return "good"; 
    } 
    if (item.NestedObject.NestedProperty == "price is missing") { 
     return "bad - category 1"; 
    } 
    return "bad - category 2"; 
} 

Answer 2

你爲什麼不只是創建一個接受兩個屬性和兩個對象，並設置狀態MyDomainItem構造？它將使MyDomainItem成爲一個更健壯的類（狀態有效性不會取決於調用者的良好意願），並且還將解決您的樣式問題。