Question

This LINQ expression is not working:

dt.AsEnumerable().ToDictionary<Int64, List<string>> (
    dtRow => dtRow.Field<Int64>("CodeVal_1"),
    new List<string> {
        dtRow => dtRow.Field<string>("CodeVal_2"), 
        dtRow => dtRow.Field<string>("CountryCode")
    }
);

dt is a DataTable, and I added a reference to DataSetExtensions.

Here full code

    using (DataSet dsIps = DbConnection.db_Select_Query("use mydb select * from tblCountryCodes"))
    {
        using (DataTable dt = dsIps.Tables[0])
        {
            dt.AsEnumerable().ToDictionary<Int64, List<string>>(
            dtRow => dtRow.Field<Int64>("CodeVal_1"),
            new List<string> {
                    dtRow => dtRow.Field<string>("CodeVal_2"), 
                    dtRow => dtRow.Field<string>("CountryCode")
                }
            );
        }
    }

errors list

Answer 1

Based on the additional information, the problem is that you are not passing the right arguments to ToDictionary. It takes two lambdas, not a lambda and a List<>.

Here’s the first step to fixed code:

dt.AsEnumerable().ToDictionary(
    dtRow => dtRow.Field<Int64>("CodeVal_1"),
    dtRow => new List<string> {
        dtRow.Field<string>("CodeVal_2"), 
        dtRow.Field<string>("CountryCode")
    }
);

EDIT: fixed using wrong version of ToDictionary.