選擇情況下，LINQ在C＃

Question

我怎樣才能trasfrom下面的SQL語句轉換成LINQ

select AdsProperties.AdsProID, 
     AdsProperties.IsActive, 
     AdsProperties.Name, 
      case 
       when AdsProperties.ControlType =1 then -- TextBox 
        'Textbox' 
       when AdsProperties.ControlType =2 then -- DropDown 
        'Dropdown' 
       when AdsProperties.ControlType =3 then -- ConboBox 
        'ComboBox' 
       else -- RadioButton 
        'RadioButtont' 
      end as ControlType 
    from CLF.utblCLFAdsPropertiesMaster as AdsProperties 

我已經試過這

var query = from AdsProperties in db.utblCLFAdsPropertiesMasters 
      select new 
      { 
       AdsProperties.AdsProID, 
       AdsProperties.Name, 
       AdsProperties.IsActive, 
       ControlType = AdsProperties.ControlType == 1 ? (int?)"TextBox" : null, 
       ControlType = AdsProperties.ControlType == 2 ? (int?)"Dropdown" : null, 
       ControlType = AdsProperties.ControlType == 3 ? (int?)"ComboBox" : null,     
       ControlType = AdsProperties.ControlType == 4 ? (int?)"RadioButton" : null) 
      }; 
      dt = query.CopyToDataTableExt(); 

但我得到這個錯誤

`an anynomous type cannot have multiple properties with the same name` 

我知道這可能很簡單。然而，作爲linq的新人，我沒有相應的經驗來處理它。任何幫助，將不勝感激。提前致謝。

Answer 1

聲明字符串數組爲：

string[] controls = new string[] {"TextBox","Dropdown","ComboBox","RadioButton"}; 

修改您的查詢如下所述：

var query = from AdsProperties in db.utblCLFAdsPropertiesMasters 
        select new 
        { 
         AdsProperties.AdsProID, 
         AdsProperties.Name, 
         AdsProperties.IsActive, 
         ControlType = AdsProperties.ControlType < controls.Length ? controls[AdsProperties.ControlType-1] : null 
        }; 
     dt = query.CopyToDataTableExt(); 

Answer 2

var query = from AdsProperties in db.utblCLFAdsPropertiesMasters 
        select new 
        { 
         AdsProperties.AdsProID, 
         AdsProperties.Name, 
         AdsProperties.IsActive, 
         ControlType = (AdsProperties.ControlType == 1) ? "TextBox" : 
             (AdsProperties.ControlType == 2) ? "Dropdown" : 
             (AdsProperties.ControlType == 3) ? "ComboBox" : 
             (AdsProperties.ControlType == 4) ? "RadioButton" : "" 
        }; 
     dt = query.CopyToDataTableExt(); 

Answer 3

您可以使用下面的代碼。

var query = from AdsProperties in db.utblCLFAdsPropertiesMasters 
    select new 
    { 
     AdsProperties.AdsProID, 
     AdsProperties.Name, 
     AdsProperties.IsActive, 
     ControlType = AdsProperties.ControlType == 1 ? "TextBox" : 
      (AdsProperties.ControlType == 2) ? "Dropdown" : 
      (AdsProperties.ControlType == 3) ? "ComboBox" : 
      (AdsProperties.ControlType == 4) ? "RadioButton" : 
      null) 
    }; 
dt = query.CopyToDataTableExt(); 

另外，如果你想使它不那麼亂，你可以嘗試把你的病情的另一種方法，並作出這樣一個電話：

var query = from AdsProperties in db.utblCLFAdsPropertiesMasters 
    select new 
    { 
     AdsProperties.AdsProID, 
     AdsProperties.Name, 
     AdsProperties.IsActive, 
     ControlType = GetControlType(AdsProperties.ControlType) 
    }; 
dt = query.CopyToDataTableExt(); 

而且你GetControlType會是這樣的：

private string GetControlType(int controlIndexOrWhatever) 
{ 
    switch(controlIndexOrWhatever) 
    { 
     case 1: return "TextBox"; 
     case 2: return "DropDown"; 
     case 3: return "ComboBox"; 
     case 4: return "RadioButton"; 
     default: return null;    
    } 
} 

但是，然後再次，它沒有測試，並不適用於實體的LINQ。我認爲它可能適用於LINQ to SQL。不介意語法問題（如果有的話），只寫代碼而不檢查VS.