title: How create a mandatory field in runtime using a ClientDataset
body: <p>I'm using this code to create a set of  fields in runtime</p>
  
  <pre><code>  ClientDataSet1.FieldDefs.Add('ID', ftInteger, 0);
    ClientDataSet1.FieldDefs.Add('Serial', ftInteger, 0);
    ClientDataSet1.FieldDefs.Add('Customer', ftString, 40);
    ClientDataSet1.FieldDefs.Add('Address', ftString, 40);
    ClientDataSet1.CreateDataSet;
  </code></pre>
  
  <p>Now I want to  make some fields mandatory, how i can define a field created in runtime as mandatory?</p>