I've got a table which has the usual ParentID, ChildID as it's first two columns in a self-referencing tree data structure.

My issue is that when I pull this out and use the following code:

DataSet set = DA.GetNewCategories();
        set.Relations.Add(
            new DataRelation("parentChildCategories", set.Tables[0].Columns["CategoryParentID"], set.Tables[0].Columns["CategoryID"])
            );
        StringBuilder buildXml = new StringBuilder();
        StringWriter writer = new StringWriter(buildXml);
        set.WriteXml(writer);
        TreeView2.DataSource = new HierarchicalDataSet(set, "CategoryID", "CategoryParentID");
        TreeView2.DataBind();

I get the error:

These columns don't currently have unique values

I believe this is because my data has children with multiple parent nodes. This is fine for my application - I don't mind if one row of data is rendered in multiple nodes of my TreeView.

Could someone shed light on this please? It doesn't seem unreasonable to have a DataSet render XML which has nodes appearing in multiple places, but I can't figure out how to do it.

Thanks,

Matt.