C# Add choice field to list and set default value

Question

I am currently writing some code that when a user presses my custom ribbon button I add a choice column to the current document list. I am using the AddAsXml to add the column, I add the choice list and set the default value, but after adding the column (field), existing items do not have a value set for this field. Do I need to iterate the whole library after adding this field or is there a way to force the field add to update the value for existing items.

Here is the code I am using:

using (var site = new SPSite(siteId))
{
    string columnName = "MyMeatChoice";

    // Check if the list contains the meat choice column
    var list = site.RootWeb.Lists[rootListId];
    var field = list.Fields.TryGetFieldByStaticName(IdShieldStatusColumn);
    if (field == null)
    {
        string newField = string.Concat("<Field Type='Choice' DisplayName='",
            columnName, "' Name='", columnName, "' ",
            "Format='Dropdown' Required='TRUE' Indexed='TRUE'><CHOICES>",
            "<CHOICE>Fish</CHOICE><CHOICE>Beef</CHOICE>",
            "<CHOICE>Chicken</CHOICE><CHOICE>Emu</CHOICE>",
            "<CHOICE>Platypus</CHOICE><CHOICE>Penguin</CHOICE>",
            "</CHOICES><Default>Penguin</Default>",
            "<Description>The type of meat that you would like to eat.",
            "</Description></Field>");

            list.Fields.AddFieldAsXml(newField, true,
                SPAddFieldOptions.AddFieldToDefaultView);
            list.Update();
    }
}

Answer 1

You need to iterate each existing items. The data contained in an item is not affected by the new fields. It only adds a new property accessible to the item. In fact, it is better like this, just to prevent to override existing values.