LINQ - 我如何使用DataSet.DataRelation來加入這些表並總計一個字段？

Question

我的LINQ查詢未在下面產生預期的輸出。基本上，它是table2.cost和table2.code和table2.class的總和，按table1.alias分類並按table1.priority排序。我在DataSet中添加了兩個DataRelation：

ds.Relations.Add("Table1Table2", ds.Tables[1].Columns("ID"), ds.Tables[2].Columns("ParentID"); 
ds.Relations.Add("Table2Table3", 
    new DataColumn[] { ds.Tables[2].Columns["Code"], ds.Tables[2].Columns["Class"] },    
    new DataColumn[] { ds.Tables[3].Columns["Code"], ds.Tables[3].Columns["Class"] }); 

var query = from aliases in table1.AsEnumerable() 
    join children in table2.AsEnumerable() on aliases("ID") equals children("ParentID") 
    orderby aliases("priority") 
    select new 
    { 
     Name = aliases("alias"), 
     Cost = 
      from data in table3.AsEnumerable() 
      group data by new { code = data("code"), classcode = data("class") } 
      into datatemp 
      select new 
      { 
       cost = datatemp.Sum(x => x("cost")) 
      } 
    }; 

任何想法我做錯了什麼？提前致謝！

table1: list of aliases and priorities 
----------------- 
alias priority 
alias1 1 
alias2 2 
alias3 4 
alias4 3

table2: children records joined to table1 by ParentID (1-to-many) 
----------------- 
code class ParentID 
code1 class1 1 
code2 class2 1 
code3 class3 2 
code4 class4 4

table3: data, joined to table2 by class and code (1-to-many) 
----------------- 
code class cost 
code1 class1 1.00 
code1 class1 10.00 
code1 class1 26.00 
code2 class2 5.00 
code2 class2 0.00 
code3 class3 1000.00

預期輸出：

alias1 42.00 
alias2 1000.00 
alias4 0.00 
alias3 0.00

Answer 1

var query = from x in Table1.AsEnumerable() 
orderby x.Field<int>("Priority") 
select new { 
    Name = x.Field<string>("alias"), 
    TotalCost = x.GetChildRows("Table1Table2") 
      .Sum(c => c.GetChildRows("Table2Table3") 
        .Sum(tx => tx.Field<decimal>("cost"))) 
};