Hi Ian and everybody else, Check out the book "trees and hierarchies in SQL for smarties" by Joe Celko. ISBN: 1-55860-920-2 It gives a very good overview about how to treat trees in a SQL database. It's really good, and it refers to the "nested set tree model" very deeply. I use SQL-Server and i wrote a couple of triggers that keep my lft, rgt and lvl values up to date. If you need them, just email me at [EMAIL PROTECTED]
Btw. The trick about not having to update so many records in a nested set tree model if you insert a node near to the top is that you do not use gaps with the size of 1 between the bottom leafs. You can use steps of eg. 10. So if you have to insert a node to the left of the topmost treenode with the left value of 1 and the left value of the first subordinate of 11 you can just insert the new record with the lft and rgt values of 2 and 3 without any further update. (check out Chapter 5 in the mentioned book called "frequent insertion trees") <cfgreetings from="[EMAIL PROTECTED]" to="reader" location="bern" country="switzerland" function="railo core developer" message="merry xmas"> -----Urspr�ngliche Nachricht----- Von: Ian Buzer [mailto:[EMAIL PROTECTED] Gesendet: Donnerstag, 23. Dezember 2004 14:51 An: CF-Talk Betreff: Re: In One? >You could set your table up in a "modified preorder tree traversal", so >each node has a "LFT" and "RGT" numeric value. I've done this in >several instances and it works great. Hey, thanks Dov, that's lovely. As far as I understand it so far, it does have the snag that if you make a change near the top of the hierachy, a whole lot of data below has to be updated. Also, in this particular instance, I'm importing the category heirachy from another app on a daily basis which uses the other schema, so I'm probably looking at a long process to convert it from one schema to another during the import. Ian ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~| Special thanks to the CF Community Suite Silver Sponsor - New Atlanta http://www.newatlanta.com Message: http://www.houseoffusion.com/lists.cfm/link=i:4:188696 Archives: http://www.houseoffusion.com/cf_lists/threads.cfm/4 Subscription: http://www.houseoffusion.com/lists.cfm/link=s:4 Unsubscribe: http://www.houseoffusion.com/cf_lists/unsubscribe.cfm?user=89.70.4 Donations & Support: http://www.houseoffusion.com/tiny.cfm/54
