Multiple WHERE clause in Linq

Question

I'm new to LINQ and want to know how to execute multiple where clause. This is what I want to achieve: return records by filtering out certain user names. I tried the code below but not working as expected.

DataTable tempData = (DataTable)grdUsageRecords.DataSource; var query = from r in tempData.AsEnumerable()             where ((r.Field<string>("UserName") != "XXXX") || (r.Field<string>("UserName") != "XXXX"))                                         select r;                  DataTable newDT = query.CopyToDataTable(); 

Thanks for the help in advance!!!

Answer 1

Well, you can just put multiple "where" clauses in directly, but I don't think you want to. Multiple "where" clauses ends up with a more restrictive filter - I think you want a less restrictive one. I think you really want:

DataTable tempData = (DataTable)grdUsageRecords.DataSource; var query = from r in tempData.AsEnumerable()             where r.Field<string>("UserName") != "XXXX" &&                   r.Field<string>("UserName") != "YYYY"             select r;  DataTable newDT = query.CopyToDataTable(); 

Note the && instead of ||. You want to select the row if the username isn't XXXX and the username isn't YYYY.

EDIT: If you have a whole collection, it's even easier. Suppose the collection is called ignoredUserNames:

DataTable tempData = (DataTable)grdUsageRecords.DataSource; var query = from r in tempData.AsEnumerable()             where !ignoredUserNames.Contains(r.Field<string>("UserName"))             select r;  DataTable newDT = query.CopyToDataTable(); 

Ideally you'd want to make this a HashSet<string> to avoid the Contains call taking a long time, but if the collection is small enough it won't make much odds.