Question

I have table with pageId, parentPageId, title columns.

Is there a way to return unordered nested list using asp.net, cte, stored procedure, UDF… anything?

Table looks like this:

PageID    ParentId    Title 1         null        Home 2         null        Products 3         null        Services 4         2           Category 1 5         2           Category 2 6         5           Subcategory 1 7         5           SubCategory 2 8         6           Third Level Category 1 ...   

Result should look like this:

Home Products     Category 1         SubCategory 1             Third Level Category 1         SubCategory 2     Category 2 Services 

Ideally, list should contain <a> tags as well, but I hope I can add it myself if I find a way to create <ul> list.

EDIT 1: I thought that already there is a solution for this, but it seems that there isn’t. I wanted to keep it simple as possible and to escape using ASP.NET menu at any cost, because it uses tables by default. Then I have to use CSS Adapters etc.

Even if I decide to go down the ‘ASP.NET menu’ route I was able to find only this approach: http://aspalliance.com/822 which uses DataAdapter and DataSet 🙁

Any more modern or efficient way?

Answer 1

Best practice would be to do this using IHierarchyData and IHierarchalEnumerable and DataBind to a custom control which inherits from HierarchalDataBoundControl (this is the base for controls like TreeView).

However, let’s try for a quick-and-dirty, not-especially-efficient, simple example in c#:

//class to hold our object graph in memory //this is only a good idea if you have a small number of items //(less than a few thousand) //if so, this is a very flexible and reusable way to represent your tree public class Page {     public string Title {get;set;}     public int ID {get;set;}     public Collection<Page> Pages = new Collection<Page>();      public Page FindPage(int id)     {         return FindPage(this, id);     }      private Page FindPage(Page page, int id)     {         if(page.ID == id)         {             return page;         }         Page returnPage = null;         foreach(Page child in page.Pages)         {             returnPage = child.FindPage(id);             if(returnPage != null)             {                 break;             }         }         return returnPage;     } }  //construct our object graph DataTable data = SelectAllDataFromTable_OrderedByParentIDAscending(); List<Page> topPages = new List<Page>(); foreach(DataRow row in data.Rows) {     Page page = new Page();     page.Title = (string)row['Title'];     page.ID = (int)row['PageID'];     if(row['ParentID'] == null)     {         topPages.Add(page);     }     else     {         int parentID = (int)row['ParentID'];         foreach(Page topPage in topPages)         {             Page parentPage = topPage.FindPage(parentID);             if(parentPage != null)             {                 parentPage.Pages.Add(page);                 break;             }         }     } }  //render to page public override void Render(HtmlTextWriter writer) {     writer.WriteFullBeginTag('ul');     foreach(Page child in topPages)     {         RenderPage(writer, child);     }     writer.WriteEndTag('ul'); }  private void RenderPage(HtmlTextWriter writer, Page page) {     writer.WriteFullBeginTag('li');     writer.WriteBeginTag('a');     writer.WriteAttribute('href', 'url');     writer.Write(HtmlTextWriter.TagRightChar);     writer.Write(page.Title);     writer.WriteEndTag('a');     if(page.Pages.Count > 0)     {         writer.WriteFullBeginTag('ul');         foreach(Page child in page.Pages)         {             RenderPage(writer, child);         }         writer.WriteEndTag('ul');     }     writer.WriteEndTag('li'); }