Set autonumber for DataTable after it already has data

Question

I have the following code to add an autonumber column to a DataTable:

public void AddAutoIncrementColumn(DataTable dt)
{
   DataColumn column = new DataColumn();
   column.DataType = System.Type.GetType("System.Int32");
   column.AutoIncrement = true;
   column.AutoIncrementSeed = 0;
   column.AutoIncrementStep = 1;
   dt.Columns.Add(column);
}

However, this value will be blank for all rows that are already in the table; it seems that the AutoIncrement is only triggered for new rows that are added after this column has been added. Is there a way to set autonumber values for the rows that already exist?

Answer 1

I don't think that it's possible to trigger the AutoIncrement functionality when the rows are already in the table. But you could update the table manually easily:

public void AddAutoIncrementColumn(DataTable dt)
{
    DataColumn column = new DataColumn();
    column.DataType = System.Type.GetType("System.Int32");
    column.AutoIncrement = true;
    column.AutoIncrementSeed = 0;
    column.AutoIncrementStep = 1;
    dt.Columns.Add(column);
    int index = -1;
    foreach (DataRow row in dt.Rows)
    {
        row.SetField(column, ++index);
    }
}