使这一LINQ投影查询更好

Question

假设我有这样的定义域类：

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;} 
} 

然后，我有一个LINQ查询，看起来像这样：根据我所知道的

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 
       } 

，我可以解决ItemStatus有两种方法：

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"; 
    } 
} 

或调用功能，在LINQ QUER解决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) 
       } 

我脑海中有些东西只是不停地说，一定有更好的办法。我真的很喜欢做的事情大致是这样的：

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"; 
         } 
        } 
       } 

是否有类似的东西，我可以做什么？

在此先感谢... !!!

Answer 1

这样的事情呢？

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"; 

虽然我会建议扩展ObjectA与属性，为您做这个评估，它在LINQ查询看起来不太好。如果你没有来源，你可以使用一个扩展方法

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

你为什么不只是创建一个接受两个属性和两个对象，并设置状态MyDomainItem构造？它将使MyDomainItem成为一个更健壮的类（状态有效性不会取决于调用者的良好意愿），并且还将解决您的样式问题。