Multiple WHERE clause in Linq

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!!!

Solution 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.

Solution 2:

The LINQ translator is smart enough to execute:

.Where(r => r.UserName !="XXXX" && r.UsernName !="YYYY")

I've tested this in LinqPad ==> YES, Linq translator is smart enough :))

Solution 3:

Also, you can use bool method(s)

Query :

DataTable tempData = (DataTable)grdUsageRecords.DataSource;
var query = from r in tempData.AsEnumerable()
            where isValid(Field<string>("UserName"))// && otherMethod() && otherMethod2()                           
            select r;   

        DataTable newDT = query.CopyToDataTable();

Method:

bool isValid(string userName)
{
    if(userName == "XXXX" || userName == "YYYY")
        return false;
    else return true;
}