LINQ query IEnumerable<Object> for IEnumerable<DataRow> results in null [duplicate]

Question

This question already has answers here:

LINQ to Entities query to DataTable (3 answers)

Closed 8 years ago.

Why is my LINQ query ("rows") showing up as a null when it seems like I have plenty of data ("waypoints")?

I'm doing an insert of ~20k records and rather than go through Entity Framework I've opted for SqlBulkCopy, which seems to mean I need a datatable. I'm trying to get an IEnumerable into IEnumberable as that seems to be the only way to get CopyToDataTable().

I was copying the syntax in this answer, and you can see in my debugger that I have plenty of objects in my original list but IEnumerable is null.

Same code, maybe easier to read:

    IEnumerable<DataRow> rows =
            (from w in waypoints.AsEnumerable()
            select w)  as IEnumerable<DataRow>;

    DataTable table = rows.CopyToDataTable();

The "rows" variable is returning as null.

Answer 1

You are trying to typecase an IEnumerable<Waypoint> as an IEnumerable<DataRow>, which is not going to work unless your Waypoint class is derived from DataRow, which I assume it's not. The documentation for the CopyToDataTable method is pretty clear:

The parameter T of the input parameter source can only be of type DataRow or a type derived from DataRow.

You are going to have to make your data table the long way, unfortunately. Make a new blank DataTable, add columns to it's Columns collection, then add rows to it's Rows collection.