从DataTable LINQ查询检索列值时发生错误

问题1:

我正在写一个查询，以获得数据表中一行的索引:

var index = from row in DataTable1.AsEnumerable()
let r = row.Field<string>("Column1") 
where r == strColumn1 
select DataTable1.Rows.IndexOf(row);

然后我尝试为多列做

var index = from row in DataTable1.AsEnumerable()
let r = row.Field<string>("Column1") && s = row.Field<int>("Column2")
&& t = row.Field<string>("Column3") && u = row.Field<string>("Column4")
where r == strColumn1 && s == intColumn2 && t == strColumn3 && u == strColumn4
select DataTable1.Rows.IndexOf(row);

有可能吗?

问题2:

从@DominicZukiewicz的回答当使用let对多个列这样，我得到一个错误:

var index = from row in DataTable1.AsEnumerable()
let r = row.Field<string>("Column1")
let s = row.Field<int>("Column2")
let t = row.Field<string>("Column3")
let u = row.Field<string>("Column4")
where r == strColumn1 && s == intColumn2 && t == strColumn3 && u == strColumn4
select DataTable1.Rows.IndexOf(row);
DataTable1.Rows[index]["Columnx"] = intUpdateValueColumnx;
DataTable1.Rows[index]["Columny"] = intUpdateValueColumny;
DataTable1.Rows[index]["Columnz"] = intUpdateValueColumnz;
DataTable1.AcceptChanges();

它的形式是:

附加信息:无法强制转换类型为'System. data . enumerablerowcollection ' 1的对象。

我哪里错了?

var index = from row in DataTable1.AsEnumerable()
   let r = row.Field<string>("Column1")
   let s = row.Field<int>("Column2")
   let t = row.Field<string>("Column3")
   let u = row.Field<string>("Column4")
   where r == strColumn1 && s == intColumn2 && t == strColumn3 && u == strColumn4
   select DataTable1.Rows.IndexOf(row);