title: Using Linq on datatable that contain numeric field
body: <p>I am using LINQ on datatable containing a Group By clause.
  One of the fields is numeric. It is defined as Numeric 6,0 in AS400.</p>
  
  <pre><code>var query = dt.AsEnumerable()
      .GroupBy(it =&gt; new
      {
          status = it.Field&lt;string&gt;("status"),
          CommentNo = it.Field&lt;?????&gt;("commentNo")
      })...
  </code></pre>
  
  <p>commentNo is the number and I do not know what type should be defined:</p>
  
  <pre><code>   CommentNo = it.Field&lt;int&gt;("commentNo") // does not work
  </code></pre>
  
  <p>I am getting the following error:</p>
  
  <pre><code>An unhandled exception of type 'System.InvalidCastException' occurred in 
  System.Data.DataSetExtensions.dll. Additional information: Specified cast is
  not valid.
  </code></pre>