對象不能從DBNull轉換到其它類型的在LINQ表達

Question

var gFieldList = new List<string>() { "Supplier", "Country" }; 
    var sFieldList = new List<string>() { "Sales"}; 

    var gField = string.Join(", ", gFieldList.Select(x => "it[\"" + x + "\"] as " + x)); 
    var sField = string.Join(", ", sFieldList.Select(y => "Sum(Convert.ToDouble(it[\""+y+"\"])) as "+y)); 


     var newSort = dataTable 
         .AsEnumerable() 
         .AsQueryable() 
         .GroupBy("new("+gField+")", "it") 
         .Select("new("+sField+",it.Key as Key, it as Data)"); 

var groupedData = (from dynamic dat in newSort select dat).ToList(); 

拋出異常

對象不能從DBNull轉換爲其他類型。

在最後一行

，

var groupedData = (from dynamic dat in newSort select dat).ToList(); 

如何解決這個問題？

Answer 1

EDIT2：試着改變你的轉換這樣

sFieldList.Select(y => "Sum(Convert.ToDouble(iif(it[\""+y+"\"] == @0,0,it[\""+y+"\"]))) as "+y) 

然後

var newSort = dataTable 
       .AsEnumerable() 
       .AsQueryable() 
       .GroupBy("new("+gField+")", "it") 
       .Select("new("+sField+",it.Key as Key, it as Data)",DBNull.Value); 

UPDATE2：圓形和結果試試這個：

sFieldList.Select(y => "Sum(Math.Round(Convert.ToDouble(iif(it[\""+y+"\"] == @0,0,it[\""+y+"\"])),2)) as "+y) 

Answer 2

試試這個：

var gFieldList = new List<string ?>() { "Supplier", "Country" }; 
var sFieldList = new List<string ?>() { "Sales"};