Hi, I had a similar problem once. I solved that by selecting all desired entries from the DB and generating a tree representation in Java.
For this to work it was required, that the entries in the Vector which Torque (i.e. a peer) returns, are ordered in such a way, that parents always come before their children. But this is usually the case as parents are normally entered into the DB before their children and thus have lower IDs or timestamps. (I had a forum then) If you were asking about a Select/Torque statement which gives all elements in preorder, then I don't have an answer. :-) Regards, Alex Will Holcomb wrote: > I am working on a program with a tree in it and because I will be > regularly be retrieving entire branches I was going to use the preorder > traversal representation for storage rather than the adjacency matrix so > as to cut down on queries. > > I am guessing this is the representation referenced in the documentation > when someone said they could load a tree with a single query and I was > just wondering if anyone could speak to the appropriateness of torque. I > don't want to spend the time learning it if it is not going to be useful. > > If anyone is unfamiliar with a preorder traversal you just walk around the > tree tracking counting when you first and last pass a node, like: (I > explained it in e-mail a couple months ago, so I have some nice ascii) > > (1) W [10] (#) - Number placed Node ID | Entry # | Exit # > v / \ ^ entering a node ========================== > v / \ ^ [#] - Number placed W | 1 | 10 > v />>>>>\ ^ leaving a node --------+---------+------- > v / ^ v \ ^ > - Movement right X | 2 | 7 > (2) X [7] v \ ^ v - Movement down --------+---------+------- > v | ^ (8) R [9] ^ - Movement up Y | 3 | 6 > (3) Y [6] >>>>>>^ --------+---------+------- > v | ^ Z | 4 | 5 > (4) Z [5] --------+---------+------- > >>>>>>^ R | 8 | 9 > --------+---------+------- > > As opposed to the more traditional adjacency matrix which would look > like: > > Node Id | Node Contents Parent | Child W > ======================= ============== / \ > W | ... W | X / \ > --------+-------------- -------+------ X R > X | ... W | R | > --------+-------------- -------+------ Y > Y | ... X | Y | > --------+-------------- -------+------ Z > Z | ... Y | Z > --------+-------------- -------+------ > > The advantage is you can get all the nodes in a branch with a single query > (entry_id > node.entry_id and exit_id < node.exit_id) and reconstruct it > pretty painlessly (if exit_id - entry_id = 1 then is a leaf). Also, you > can get the path back to the root with a single query which is handy > sometimes. > > The downside is that adding or moving a node requires changing the id's of > all the nodes to the right. How to do that sort of operation is what I am > uncertain about in torque. Also, the querries to get branches and stuff > are not normal sort of mapping. Anyone have any useful info? > > Will > > -- > To unsubscribe, e-mail: <mailto:[EMAIL PROTECTED]> > For additional commands, e-mail: <mailto:[EMAIL PROTECTED]> -- Mit freundlichen Gr��en Alexander Banthien _______________________________________ Questech GmbH Schwarzwaldstr. 19 79199 Kirchzarten Fon: +49 (0)7661 90 35-15 Fax: +49 (0)7661 90 35-20 www.questech.de _______________________________________ -- To unsubscribe, e-mail: <mailto:[EMAIL PROTECTED]> For additional commands, e-mail: <mailto:[EMAIL PROTECTED]>
