C# – LINQ and paging with a DataTable – can’t get Skip working

cdatatablelinq

Ok so this might be a dumb question, but I can't seem to figure it out. I thought I'd try out LINQ against a DataTable. I got my query working and now I'm trying to implement some simple paging.

DataTable dataTable = null;

dataTable = GetAllDataTables();

var query = from r in dataTable.AsEnumerable()
            orderby r.Field<string>(Constants.fileName)
            select r;

query.Skip(WPP_PAGE_SIZE * pageIndex).Take(WPP_PAGE_SIZE);

My problem is that I get an error at query.Skip(…).

Error 1 'System.Data.OrderedEnumerableRowCollection'
does not contain a definition for
'Skip' and no extension method 'Skip'
accepting a first argument of type
'System.Data.OrderedEnumerableRowCollection'
could be found (are you missing a
using directive or an assembly
reference?)

References I have:

Microsoft.SharePoint
System
System.Core
System.Data
System.Data.DataSetExtensions
System.Web
System.Xml

What am I missing?

Best Answer

You need using System.Linq; at the top of your file.

A second problem is that you need to assign the result of Skip and Take to something otherwise the result is simply discarded:

var query2 = query.Skip(WPP_PAGE_SIZE * pageIndex).Take(WPP_PAGE_SIZE);

Related Solutions

C# – LINQ query on a DataTable

You can't query against the DataTable's Rows collection, since DataRowCollection doesn't implement IEnumerable<T>. You need to use the AsEnumerable() extension for DataTable. Like so:

var results = from myRow in myDataTable.AsEnumerable()
where myRow.Field<int>("RowNo") == 1
select myRow;

And as @Keith says, you'll need to add a reference to System.Data.DataSetExtensions

AsEnumerable() returns IEnumerable<DataRow>. If you need to convert IEnumerable<DataRow> to a DataTable, use the CopyToDataTable() extension.

Below is query with Lambda Expression,

var result = myDataTable
    .AsEnumerable()
    .Where(myRow => myRow.Field<int>("RowNo") == 1);

C# – When to use .First and when to use .FirstOrDefault with LINQ

I would use First() when I know or expect the sequence to have at least one element. In other words, when it is an exceptional occurrence that the sequence is empty.

Use FirstOrDefault() when you know that you will need to check whether there was an element or not. In other words, when it is legal for the sequence to be empty. You should not rely on exception handling for the check. (It is bad practice and might hurt performance).

Finally, the difference between First() and Take(1) is that First() returns the element itself, while Take(1) returns a sequence of elements that contains exactly one element.

Best Answer

Related Solutions

C# – LINQ query on a DataTable

C# – When to use .First and when to use .FirstOrDefault with LINQ

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