Filtering Datatables

Years back there was this crazy way of dealing with data in .NET called a DataSet. DataSets contained DataTables which contained a combination of DataRows and DataColumns. It was all loosely typed and keyed with strings. Basically a database inside of your process. Even when they were cool I felt uncomfortable using them. Because I sometimes maintain legacy code I run into these monstrosities.

Today’s problem was that I needed to filter the contents of a table before bulk loading it. You can actually do simple filtering using a quasi-SQL like

   var dataRows = existingDataTable.Select("UserName = 'simon'")

This gives you back a collection of DataRows which I guess you could inset back into the table after clearing it of rows. To make this useful there is an extension method called CopyToDataTable in System.Data.DataExtension (be sure to include the dll for this). Using that you can get back a full data table

var dataTable = existingDataTable.Select("UserName = 'simon'").CopyToDataTable();

In that same package, though, is a much better tool for filtering: converting the table to an IEnumerable. You still need to use some magic strings but that’s somewhat unavoidable in data tables.

var dt = existingDataTable.AsEnumerable()
                    .Where(r => r.Field<String>("UserName") == "Simon").CopyToDataTable();

You can also do more advanced things like checking to see if something is a GUID

var dt = existingDataTable.AsEnumerable()
                    .Where(r => Guid.TryParse(r.Field<String>("Id"), out var _)).CopyToDataTable();