Type Of Data In GridView / Listview Bound - Template And Auto Generated Fields

Background: I'm populating lots of asp.net c# GridViews and ListViews from a database and subsequently users may export them to Excel. I want export as native Excel (not html). I can't use office automation, and I'm using JET which works fine. I have no control over users' machines. Question: When doing the export, you have to tell Jet what type each field is, in my case "text" (varchar) or "numeric" (double). The difference is that if you export a numeric column, the users can sum the data in Excel, where as strings are exported with a leading apostrophe and so are not much use in arithmetic.

Currently I parse the first data row of the Grid/ListView, check if each value is numeric or text, and assign a type to the column accordingly. That works, except for when I have something in the first column which looks numeric but in fact is a text string. I don't want to parse every row in order to be sure I have the correct data type as some of these exports are quite large. When I load the Grid/ListView from the database, the database certainly knows what type each field is. So my question is... how do I extract the type of the database item behind a a Grid/ListView item? I could explicitly code it as an attribute on the item, but that's duplicating information I already have, if only I can get to it. I know that where I have a DataTable then I can get the underlying type from that, but mostly I don't have tables handy, just the Grid/ListView. Note that Jet will throw if you try to insert an empty string into a nullable numeric column. The way to do this is to omit that column name from the insert statement, or output a zero.