MS ACCESS - Hierarchical tree sort - ms-access

Question

I'm struggling with a sorting problem.
I've got a table which is as follows:
aspect_id (int)
aspect_text (memo)
root_id (int) which has as a foreign key a aspect_id
I've got a non cyclic tree with the following dummy data:
aspect_id aspect_text root_id
1 root null
2 aspect1 1
3 aspect2 1
4 aspect3 2
5 aspect5 4
In the example the data is sorted correctly, in my database its not. I want to sort that it starts at the root element, then finds a child, output that child and does that recursively.
With CTE it is fairly doable. Access doesn't support this. With CTE it would be something like:
WITH aspectTree (aspect_id, root_id, Level#) AS
(
Select
aspect.aspect_id,
aspect.root_id,
0
FROM aspect
WHERE aspect.aspect_id = 44
UNION ALL
SELECT
aspect.aspect_id,
aspect.root_id,
T.Level# + 1
FROM aspect
INNER JOIN aspectTree AS T
On T.aspect_id = aspect.root_id
)
SELECT * FROM aspectTree;

Answer 1

If performance is not a consideration, this fairly simple solution would work:
Public Function GetLevel(ByVal lngNodeId As Long) As Long
Dim varRootId As Variant
varRootId = DLookup("root_id", "aspect", "aspect_id=" & lngNodeId)
If IsNull(varRootId) Then
GetLevel = 0
Else
GetLevel = GetLevel(varRootId) + 1
End If
End Function
You could then use that function in your ORDER BY clause:
SELECT aspect.*
FROM aspect
ORDER BY GetLevel([aspect_id]), aspect_text

Answer 2

I don't know if the following will work for you but here you go using Bill of Materials algorithms.
Bill Of Materials
BOM, with Joe Celko Nested Sets

Answer 3

Its full of test code, but i did something that works in vb code. Its really ugly and slow, but it works. Im now cleaning it up, just got it working. The solution is a recursive function. The function calls on itself if it finds that the node has childs. It seemed to overwrite the arrays, that why its an array of arrays. The code is hideous, but it works and thats all i needed. The database is and will stay small (<1000 records) so speed is not an issue. Thanks for the comments and answers, if someones knows i better solution, i would love to hear it.
Private Function Fillarray(value As Integer)
Dim done As Boolean
j = j + 1
esql = "select aspect_id from aspect where root_id = " & value
Set rec(j) = db.OpenRecordset(esql)
Dim k As Integer
k = j
Do While Not rec(k).EOF
done = True
arra(i) = rec(k).Fields(0)
Dim temp1 As String
temp1 = DLookup("[aspects]", "[aspect]", "[aspect_id] = " & rec(k).Fields(0))
db.Execute "INSERT INTO sortedaspect (aspect_id, aspect) VALUES (" & rec(k).Fields(0) & ", '" & temp1 & "')"
esql = "select aspect_id from aspect where root_id = " & rec(k).Fields(0)
Set rec(90) = db.OpenRecordset(esql)
Do While Not rec(90).EOF And done
'fix this without a loop,you only need to know if it has childs...
Fillarray (rec(k).Fields(0))
done = False
Loop
'next child
rec(k).MoveNext
'value = arra(i)
i = i + 1
'MsgBox arra(i - 1)
Loop
End Function