How to build an infinite tree hierarchy? - asp.net

Question

I've been working on this since yesterday and I'm completely stumped. I'm working in VB.NET but I can understand C# if you'd prefer to answer it that way.
Basically I have items from a SQL database with IDs and parent IDs and I need to put them in a tree like so:
<ul>
<li>Some item
<ul>
<li>Another item
<ul>
<li>This could go forever
<ul>
<li>Still going</li>
</ul>
</li>
</ul>
</li>
</ul>
</li>
</ul>
Currently I have a nested repeater which works but it only gets me to the second level. It looks something like this:
<asp:Repeater ID="parent" runat="server">
<ItemTemplate>
<ul>
<li><span><%#Container.DataItem("Name")%></span>
<asp:Repeater ID="child" DataSource='<%#CType(Container.DataItem, DataRowView).Row.GetChildRows("relation")%>' runat="server">
<ItemTemplate>
<ul>
<li><span><%#Container.DataItem("Name")%></span></li>
</ul>
</ItemTemplate>
</asp:Repeater>
</li>
</ul>
</ItemTemplate>
</asp:Repeater>
The relation is like this:
ds.Relations.Add("relation",
ds.Tables("Items").Columns("ID"),
ds.Tables("Items").Columns("ParentID"),
False)
I understand why it won't work because it doesn't have a template to continue the tree. So I'm trying to figure out a way around that.
I've considered writing a function to just build the string in the code behind and stick it in the html with an asp tag. I wasn't sure how to go about this while pulling the data out of the database.

Answer 1

I found a temporary solution though it's extremely inefficient. In case anyone stumbles across my question this will at least get you by. For large amounts of data it could take up to a full minute to load.
If anyone could comment on how to make this more efficient that would be nice.
Code behind:
Private Dim dt As New DataTable
Public Function BuildTree(ByVal ID As String) As String
Dim sb As New StringBuilder
dt = YourDatabase.GetChildren(ID) '<-- You'll have to write this function
sb.AppendLine("")
If dt.Rows.Count > 0 Then
sb.AppendLine("<ul>")
If dt.Rows.Count > 1 Then
For Each row As DataRow In dt.Rows
sb.AppendLine("<li>" & row("ItemName"))
' Recursive call
sb.AppendLine(BuildTree(row("ID").ToString))
sb.AppendLine("</li>")
Next
Else
sb.AppendLine("<li>" & dt.Rows(0)("ItemName").ToString & "</li>")
End If
sb.AppendLine("</ul>")
End If
Return sb.ToString
End Function
Then in your aspx page do something like this:
<%#BuildTree(Container.DataItem("ID").ToString)%>
EDIT: Declaring the DataTable outside of the function helps the efficiency a bit.