title: A column named 'Item' already belongs to this DataTable
body: <p>I am trying to convert a <code>List</code> to a <code>datatable</code> with an extension method. Implementation is: </p>
  
  <p><b>Extension method</b></p>
  
  <pre><code>public static class list2Dt
      {
          public static DataTable ToDataTable&lt;T&gt;(List&lt;T&gt; items)
          {
              DataTable dataTable = new DataTable(typeof(T).Name);
  
              //Get all the properties
              PropertyInfo[] Props = typeof(T).GetProperties(BindingFlags.Public | BindingFlags.Instance);
              foreach (PropertyInfo prop in Props)
              {
                  //Setting column names as Property names
                  dataTable.Columns.Add(prop.Name);
              }
              foreach (T item in items)
              {
                  var values = new object[Props.Length];
                  for (int i = 0; i &lt; Props.Length; i++)
                  {
                      //inserting property values to datatable rows
                      values[i] = Props[i].GetValue(item, null);
                  }
                  dataTable.Rows.Add(values);
              }
              //put a breakpoint here and check datatable
              return dataTable;
          }
      }
  </code></pre>
  
  <p><b>Controller</b></p>
  
  <pre><code>var noDups = firstTable.AsEnumerable()
                              .GroupBy(d =&gt; new
                              {
                                  name = d.Field&lt;string&gt;("name"),
                                  date = d.Field&lt;string&gt;("date")
                              })
                              .Where(d =&gt; d.Count() &gt; 1) 
                              .Select(d =&gt; d.First())
                               .ToList();
  
                          DataTable secondTable = new DataTable();
                          secondTable.Columns.Add("name", typeof(string));
                          secondTable.Columns.Add("date", typeof(string));
                          secondTable.Columns.Add("clockIn", typeof(string));
                          secondTable.Columns.Add("clockOut", typeof(string));
  
                          secondTable = list2Dt.ToDataTable(noDups);
  </code></pre>
  
  <p>I am getting this following error: </p>
  
  <pre><code>An exception of type 'System.Data.DuplicateNameException' occurred in System.Data.dll but was not handled in user code
  
  Additional information: A column named 'Item' already belongs to this DataTable.
  </code></pre>
  
  <p>Above error is raised on line:  </p>
  
  <pre><code>dataTable.Columns.Add(prop.Name);
  </code></pre>
  
  <p>Can someone find where problem lies. </p>