static private void MakeTableWithUniqueConstraint()
{
    // Create a DataTable with 2 DataColumns.
    DataTable dataTable = new DataTable("dataTable");
    DataColumn idColumn = new DataColumn(
        "id", System.Type.GetType("System.Int32"));
    DataColumn nameColumn = new DataColumn(
        "Name", System.Type.GetType("System.String"));
    dataTable.Columns.Add(idColumn);
    dataTable.Columns.Add(nameColumn);

    // Run procedure to create a constraint.
    AddUniqueConstraint(dataTable);

    // Add one row to the table.
    DataRow dataRow;
    dataRow = dataTable.NewRow();
    dataRow["id"] = 1;
    dataRow["Name"] = "John";
    dataTable.Rows.Add(dataRow);

    // Display the constraint name. 
    Console.WriteLine(
        dataTable.Constraints[0].ConstraintName);

    // Try to add an identical row, 
    // which throws an exception.
    try
    {
        dataRow = dataTable.NewRow();
        dataRow["id"] = 1;
        dataRow["Name"] = "John";
        dataTable.Rows.Add(dataRow);
    }
    catch (Exception ex)
    {
        Console.WriteLine(
            "Exception Type: {0}", ex.GetType());
        Console.WriteLine(
            "Exception Message: {0}", ex.Message);
    }
}
static private void AddUniqueConstraint(
    DataTable dataTable)
{
    // Create the DataColumn array.
    DataColumn[] dataColumns = new DataColumn[2];
    dataColumns[0] = dataTable.Columns["id"];
    dataColumns[1] = dataTable.Columns["Name"];

    // Create the constraint on both columns.
    UniqueConstraint uniqueConstraint =
        new UniqueConstraint("idNameConstraint", dataColumns);
    dataTable.Constraints.Add(uniqueConstraint);
}