Note that using recursion bombed with more than 4000 rows due to a stack overflow. better to do non recursive:

using (DbDataReader rdr = cmd.ExecuteReader()) { if (!rdr.HasRows) return; treeView1.BeginUpdate(); while (rdr.Read()) { TreeNode parent = GetNode(rdr["parent_cat_id"]); TreeNode current = GetNode(rdr["cat_id"]); current.Text = rdr["cat_title"].ToString(); if (parent != null) { treeView1.Nodes.Remove(current); parent.Nodes.Add(current); } } treeView1.EndUpdate(); }

but recursive:

using (DbDataReader rdr = cmd.ExecuteReader()) { if (!rdr.HasRows) return; treeView1.BeginUpdate(); LoadNodes(rdr); treeView1.EndUpdate(); } /* Here's the load routine */ private void LoadNodes(DbDataReader rdr) { if (!rdr.Read()) return; TreeNode parent = GetNode(rdr["parent_cat_id"]); TreeNode current = GetNode(rdr["cat_id"]); current.Text = rdr["cat_title"].ToString(); if (parent != null) { treeView1.Nodes.Remove(current); parent.Nodes.Add(current); } LoadNodes(rdr); }

Both ways requiretheGetNode method:

private TreeNode GetNode(object key) { if (DBNull.Value.Equals(key)) return null; TreeNode[] nodes = treeView1.Nodes.Find(key.ToString(), true); TreeNode node; if (nodes.Length == 0) node = treeView1.Nodes.Add(key.ToString(), string.Empty); else node = nodes[0]; return node; }

Hey angry. . .

One thing to consider, do you want to load the entire table at one time???

My suggestion would be to populate judiciously using a 'Lazy Load' pattern

Thanks Blair but lazy loading leads to additional database hits... and I like everything to be loaded at startup.

well. . . give me a few moments and I will show one way, but still, if you dont hit the db every time a node is selected, how do you find changes?

unless this is not a concern, which is possible.

At any rate, 'Lazy Load' does not require a hit against the database everytime. Lazy Load against the in memoryDataTable.

and still it only depends on the size of the category table. . . If it is small, then a recursive load isn't that bad. . . though if it is a DataTable in memory, firstusing a Sort on cat_id, parent_id and a non recursive approach would be optimal.

Give me a moment and I will show a recursive approach. . .

Is this an coursework assignment???

Be honest. . . I will help you if it is!

But if it is, it doesn't do you any justice just giving you the answer as opposed to showing you how to approach any solution that requires recursion.

Make sense???

Thanks for your follow-up. I need it for a program I'm writing for a client.

I'm already using a DataTable but I don't want that. I want to use a DataReader because it's faster.

Please note..
- I don't want to find changes.
- Category tables contains around 500 rows.

Note that using recursion bombed with more than 4000 rows due to a stack overflow. better to do non recursive:

using (DbDataReader rdr = cmd.ExecuteReader()) { if (!rdr.HasRows) return; treeView1.BeginUpdate(); while (rdr.Read()) { TreeNode parent = GetNode(rdr["parent_cat_id"]); TreeNode current = GetNode(rdr["cat_id"]); current.Text = rdr["cat_title"].ToString(); if (parent != null) { treeView1.Nodes.Remove(current); parent.Nodes.Add(current); } } treeView1.EndUpdate(); }

but recursive:

using (DbDataReader rdr = cmd.ExecuteReader()) { if (!rdr.HasRows) return; treeView1.BeginUpdate(); LoadNodes(rdr); treeView1.EndUpdate(); } /* Here's the load routine */ private void LoadNodes(DbDataReader rdr) { if (!rdr.Read()) return; TreeNode parent = GetNode(rdr["parent_cat_id"]); TreeNode current = GetNode(rdr["cat_id"]); current.Text = rdr["cat_title"].ToString(); if (parent != null) { treeView1.Nodes.Remove(current); parent.Nodes.Add(current); } LoadNodes(rdr); }

Both ways requiretheGetNode method:

private TreeNode GetNode(object key) { if (DBNull.Value.Equals(key)) return null; TreeNode[] nodes = treeView1.Nodes.Find(key.ToString(), true); TreeNode node; if (nodes.Length == 0) node = treeView1.Nodes.Add(key.ToString(), string.Empty); else node = nodes[0]; return node; }

Worked. Many thanks.

But I'm having an empty node as the root node of the treeview!

I want my main categories (the ones that has PARENT_ID = 0) to appear without a parent nodes.

I really appreciate your help.

ahh. . I think it is because I used 'null' for top level, not '0'. . .

which is probably more proper. . . If it has no parent, parent is null.

A value of zero would mean parent iszero

But if you want zero to be top- change this line:

if (DBNull.Value.Equals(key)) return null;

to

if (DBNull.Value.Equals(key) || key.Equals(0)) return null;

Worked. Thank you so much.

Hi, can you show what the SQL was for that Self-Join table? I've have a similar problem to solve.

Hey Blair. I was reading this post and trying to figure out poplulating a winform Tree control with a self join table. I'm not getting anywhere. What does the SQL look like? I know it's an Inner Join with parent_id as foreign key. But when I tried the code, I didn't get the expected result. I just got 1 level of the Tree with no children levels.

Thanks in advance for any help. Best, Matt

Thank you for this example. I'm close but not quite there. I have a single table where rows are arranged hierarchically via their PK / FK relationships.

The table is named NODE_DESCR:
Row #1 has ID= 0, node_descrID=0 and has name="Scenario"
Row #2 has ID= 1, node_descrID=0 and has name="Aircraft"
Row #3 has ID= 1, node_descrID=0 and has name="Facility", etc.

I thought I'd be able to simply use the pattern above but refer to
TreeNode parent = GetNode(rdr["ID"]);
TreeNode current = GetNode(rdr["node_descrID"]); // or rdr["ID"] ???
current.Text = rdr["name"].ToString();

but when I exercise the following piece the appication seems to spin and I have to kill it.
if (parent != null)
{
treeView1.Nodes.Remove(current);
parent.Nodes.Add(current);
}

Any chence you could help me get last piece? I tried both the recursive and non.

Thanks much,
eric

Here's the sample code

Dim oDataSet As New DataSet
Public Sub PopulateTree(ByVal ParentId As String, ByVal TVNode As TreeNode)
Dim oDataView As New DataView(oDataSet.Tables(0), "ParentID='" & ParentId & "'",
"DATA", DataViewRowState.OriginalRows)
Dim oDataRow As DataRowView
For Each oDataRow In oDataView
Dim oTreeNode As New TreeNode(oDataRow("DATA"))
Dim oComboBox As New ComboBox
If TVNode Is Nothing Then
Else
TVNode.Nodes.Add(oTreeNode)
PopulateTree(oDataRow("ID"), oTreeNode)
End If
Next
End Sub


Read In Details http://muruganad.com/ASP.NET/ASP-.NET-How-to-Populate-a-TreeView-Control-With-TreeNode-s-Using-recursive-algorithm-or-recursion-.html

Thanks

Murugan Andezuthu Dharmaratnam