private void CreateConstraint(DataSet dataSet)
{
   // Create the ForignKeyConstraint with two DataColumn objects.
   DataColumn parentCol = dataSet.Tables["Customers"].Columns["id"];
   DataColumn childCol = dataSet.Tables["Orders"].Columns["OrderID"];
   ForeignKeyConstraint fkeyConstraint =
      new ForeignKeyConstraint("fkConstraint", parentCol, childCol);

   // Test against existing members using the Equals method.
   foreach(ForeignKeyConstraint testConstraint in 
       dataSet.Tables["Orders"].Constraints)
   {
      if(fkeyConstraint.Equals(testConstraint)){
         Console.WriteLine("Identical ForeignKeyConstraint!");
          // Insert code to delete the duplicate object, 
          // or stop the procedure.
      }
   }
}