c# - Linq query is not executing properly -

i'am trying sum datatable column's in linq. when program running foreach loop not executing. checked milion times if column names equal datatable.

resultdatatable.columns.add("user id"); resultdatatable.columns.add("amount"); resultdatatable.columns.add("order number");   var query = row in result.asenumerable()             group row row.field<string>("user id") grp                             select new             {                 id = grp.key,                 sum = grp.sum(r => r.field<int>("amount")),                 sum2 = grp.sum(r => r.field<int>("order number"))                    };  foreach(var item in query) {     resultdatatable.rows.add(item.id, item.sum, item.sum2); } 

the result datatable 3 columns. first 1 name , last name, second 1 number , third number also.

any ideas why doesn't work?

i assume have created source table in same way destination table, adding columns manually. guess contained string-columns instead of int columns. note default string.

so following creates , adds 3 columns of type string:

resultdatatable.columns.add("user id"); resultdatatable.columns.add("amount"); resultdatatable.columns.add("order number"); 

instead use overload:

resultdatatable.columns.add("user id"); resultdatatable.columns.add("amount", typeof(int)); resultdatatable.columns.add("order number", typeof(int)); 

why important? because otherwise can't use sum = grp.sum(r => r.field<int>("amount")) since column's type isn't int string , you'll runtime invalidcastexception in field @ foreach. maybe have empty try...catch somewhere swallows exception , should avoided.

a better way create table , columns, if destination table has same columns use datatable.clone:

datatable resultdatatable = result.clone(); // same columns empty