how to export data in Excel file from database in web API2.0

// GET api/values/
    public HttpResponseMessage Get()
    {

        //DataTable Dt= GetData();  Getdata from database in thr form d
        //Generate  html table sturcture
        string str = "<table><tr> <th>colume1</th></tr><tr> <td>abc</td> </tr></table>";
        HttpResponseMessage result = new HttpResponseMessage(HttpStatusCode.OK);
        result.Content = new StringContent(str);
        result.Content.Headers.ContentType = new MediaTypeHeaderValue("application/vnd.ms-excel");
        result.Content.Headers.ContentDisposition = new ContentDispositionHeaderValue("attachment"); //attachment will force download
        result.Content.Headers.ContentDisposition.FileName = "data.xlsx";
        return result;
    }