title: How to filter a linq to sql query by using textbox input
body: <p>Here is my code:</p>
  
  <pre><code>    private void textBox1_TextChanged(object sender, EventArgs e)
      {
          //**************************************
          int aa = textBox1.Text.Length;
  
          var qry = (from p in dc.Products
                     where p.ProductName.Substring(aa) == textBox1.Text.Trim()
                     select p).ToList();
          productDataGridView.DataSource = qry;
      }
  </code></pre>
  
  <p>When I enter a letter in the textbox the datagrid become empty</p>