Casting generic datatable to typed datatable

Question

I need to reuse a DataAccess method prescribed by client. This method returns a vanilla datatable. I want to cast this datatable to my Typed datatable. The amount of columns and their types will match. The exception message "Unable to cast object of type 'System.Data.DataTable' to type 'MarketValueDataTable'." is very clear, but how do I fix it?

Had a look at casting-a-base-type-to-a-derived-type, but could not see how to make that work.

I cannot populate the datatable with a datareader, can only use the client's DataAccess method.

Answer 1

The cast could only work if the table returned by the method was actually an instance of MarketValueDataTable. If it's not, all you can do is copy the data to an instance of MarketValueDataTable. You could for instance use the Merge method :

DataTable data = GetData();
MarketValueDataTable myData = new MarketValueDataTable();
myData.Merge(data);

Answer 2

Use this handy function to convert a regular DataTable to a typed DataTable.

VB

Public Shared Function ConvertToTypedDataTable(Of T As {Data.DataTable, New})(dtBase As Data.DataTable) As T
    Dim dtTyped As New T
    dtTyped.Merge(dtBase)

    Return dtTyped
End Function

Usage

Dim dtTyped = ConvertToTypedDataTable(Of dataset1.MyTypedDataTable)(MyUntypedDataTable)

C#

public static T ConvertToTypedDataTable<T>(System.Data.DataTable dtBase) where T : Data.DataTable, new()
{
    T dtTyped = new T();
    dtTyped.Merge(dtBase);

    return dtTyped;
}

Usage

dataset1.MyTypedDataTable dtTyped = ConvertToTypedDataTable<dataset1.MyTypedDataTable>(MyUntypedDataTable);