ASP.NET DropDownList bound to data but allows for nulls?

I'm using LINQ to SQL and want to be able to select a parent or no parent. Let's say I have a People table with PersonId, Name and ParentId columns. In ASP I want to enter the name, select a parent and click 'Add' to create a new Person record, but I also want to be able to leave the ParentId null. Don't ask why, this is just a simplified explanation for what I want to do.

<asp:LinqDataSource ID="LinqPeople" runat="server" 
    ContextTypeName="MyDataContext" EntityTypeName="" 
    Select="new (PersonId, Name)" TableName="People"/>
<asp:TextBox ID="textName" runat="server" />
<asp:DropDownList runat="server" ID="dropParent"
    DataSourceID="LinqPeople" DataTextField="Name" DataValueField="PersonId" />
<asp:Button ID="buttonAddPerson" runat="server" Text="Add" />

Is there any way to display 'None' in the list box with a value of null? I have thought of a few options, which is best or are there any others?

1. Create a stored procedure for the SQL "SELECT PersonId, Name FROM People UNION SELECT Null, 'NONE'"

2. Add a CheckBox for "NO PARENT"

3. Put a ListItem in the markup for the DropDownList

4. Add the item on the DataBound event handler

I found a better way, adding a ListItem in the markup:

<asp:LinqDataSource ID="LinqPeople" runat="server" 
    ContextTypeName="MyDataContext" EntityTypeName="" 
    Select="new (PersonId, Name)" TableName="People"/>
<asp:TextBox ID="textName" runat="server" />
<asp:DropDownList runat="server" ID="dropParent"
        DataSourceID="LinqPeople" DataTextField="Name" DataValueField="PersonId">
    <asp:ListItem Value="">(none)</asp:ListItem>
</asp:DropDownList>
<asp:Button ID="buttonAddPerson" runat="server" Text="Add" />

I cannot find a开发者_开发百科ny way to return the actual value 'NULL' in SelectedValue however, but I can handle that I guess. I think the ListItem way is the best because it is defined in the markup and doesn't require any code...

Don't think you can set the value of NULL since it's a string type.

I don't like the check for NULL, typically, I would use something that doesn't make sense, like -1 or something and check for that. You could also assume that your selected index is 0, however, that could cause problems somewhere else in code if you don't follow throughout the app.