LINQ - 我如何使用DataSet.DataRelation加入这些表和总结一个领域？(LIN

我的LINQ查询不产生低于预期的输出。基本上，它是对应于table2.code和table2.class通过table1.alias分类，并通过table1.priority下令table3.cost的总和。我添加了两个的DataRelation的到DataSet：

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，我做错了什么？提前致谢！

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

预期输出：

alias1 42.00
alias2 1000.00
alias4 0.00
alias3 0.00

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")))
};