LINQ - 如何使用 DataSet.DataRelation 来连接这些表并对一个字段求​​和？

Question

我的 LINQ 查询没有产生下面的预期输出。基本上，它是与 table2.code 和 table2.class 对应的 table3.cost 的总和，按 table1.alias 分类并按 table1.priority 排序。我向数据集中添加了两个 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"))
            }
    };

知道我做错了什么吗？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

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")))
};