Populating treeview from database/structure

[jamesdraughn]

Hi, I am new to these forums, first time post. I usually struggle through a problem until I figure out the solution, but I am stumped.

I have a table in an access database with the following fields.

ID:
ParentID:
Name:


So, I might have the following data:
ID|ParentID|Name
1, 1, Parent1
2, 1, Child1
3, 3, Parent2
4, 2, Grandchild1

As you can probably guess, ID is a unique autoincrementing number, while parent ID is the ID of the record that is the parent of the current record.

In the treeview, I want to be able to take that info, and generate the treeview as such.
A treeview from the above sample table would like simliar to the following:

- Parent1
- Child1
- GrandChild1
- Parent2

The reason why I titled this post database/structure is because each seperate record in the database is loaded into a new instance of a class which contains properties for each of the fields (name, id, parentid), and each of those instances of the class are loaded into the hashtable, the key being the ID, and the value being the instance of the class. (may just change it to a structure later, but for now a simple class meets my needs, and is upgradeable in the future to hold some subs or functions if needed).

It's easy to populate the tree with the Parents, I just check to see if ID = ParentID, after that I need to check the ParentID's to the tag value of each node in the tree (which I made = to the ID of the record), and if so, then add a node under that node. I have came very close, and actually got it all working as long as there are no grandchildren or deeper (greatgrandchildren?).

If anyone can give me some tips on how to make this work, I would be greatly appreciative. I have been stuck on this for a couple of weeks and all other programming has halted until I can get passed this hurdle. Thanks.

[RichardAtherton]

List below is some sample code which populates a treeview freo a database.

Since I required more properties than the stnadard TreeNode, I created a class which inherited the standard TreeNode and added my own properties.

New TreeNode Class
___________________

Public Class ViewNode
Inherits TreeNode

Public Name As String
Public Proprty As Integer
Public Unit As Integer


Sub New(ByVal Title As String, ByVal Proprty1 As Integer, ByVal Unit1 As Integer)
MyBase.New()
Name = Title
Proprty = Proprty1
Unit = Unit1
Me.Text = Name
End Sub
End Claass.

The in the load event of the form:

Private Sub PropertyAvailable_Load(ByVal sender As Object, ByVal e As System.EventArgs) Handles MyBase.Load
Dim OledbStr As String = "Select * from Localities "
Dim Cmd1 As OleDbCommand = New OleDbCommand(OledbStr, Cn1)
Cn1.Open()
Cn2.Open()
Cn3.Open()
Dim dr1 As OleDbDataReader = Cmd1.ExecuteReader()
TreeView1.BeginUpdate()
TreeView1.Nodes.Clear()
Dim AllNode As New ViewNode("All Properties", 0, 0)
TreeView1.Nodes.Add(AllNode)
<<< Sets Top level Node >>>
Dim TreePos As Integer = 1
While dr1.Read
Dim LocNode As New ViewNode(dr1("Locality"), 0, 0)
AllNode.Nodes.Add(LocNode)
<<< Sets Parent Node >>>
OledbStr = "Select * from PropAvail where Locality = '" & Trim(dr1("Locality")) & "'"
Dim Cmd2 As OleDbCommand = New OleDbCommand(OledbStr, Cn2)
Dim dr2 As OleDbDataReader = Cmd2.ExecuteReader()

While dr2.Read
Dim PropNode As New ViewNode((Trim(dr2("Adr1")) & "," & Trim(dr2("Adr2"))), dr2("Proprty"), 0)
LocNode.Nodes.Add(PropNode)
<<< Sets Child Node >>>
OledbStr = "Select * from PropUnitAvailable where Proprty = " & CStr(dr2("Proprty"))
Dim Cmd3 As OleDbCommand = New OleDbCommand(OledbStr, Cn3)
Dim dr3 As OleDbDataReader = Cmd3.ExecuteReader()
Dim Headline As String
While dr3.Read
If IsDBNull(dr3("Headline")) Then
Headline = "No Headline"
Else
Headline = dr3("Headline")
End If

Dim UnitNode As New ViewNode((Trim(dr3("PropertyAdr")) & "," & Trim(Headline)), dr3("Proprty"), dr3("Unit"))
PropNode.Nodes.Add(UnitNode)
<<< Sets Grandchild Node >>>
End While
dr3.Close()
Cmd3 = Nothing
End While
dr2.Close()
Cmd2 = Nothing

End While
TreeView1.EndUpdate()
Cmd1 = Nothing
Cn1.Close()
Cn2.Close()
Cn3.Close()

End Sub


In this particular case the nesting is 3 levels but using this technique there is no real limit to the depth of the treeview


Hope this helps.

[Edneeis]

Hopefully Richard's code will take care of you otherwise here is some info on converting between a flat structure and a heirarchy structure.

http://www.vbcity.com/forums/topic.asp?tid=56326

[ost]

I had the same problem a couple of days ago... this example helped med a lot

Treeview Interface