Hi
Please correct me if I am wrong, but I thought that root node will have
left and right value, if that is not the case I reckon best is to keep
it as 1.
Thanks
Ali
Dalibor Karlović wrote:
On Monday 27 July 2009 10:33:29 Nick Pack wrote:
Hey All,
I recently added a new proposal draft to the wiki for a new component, I
am attempting to get out of the box support for the modified preorder
tree traversal algorithm, I have some working code kindly provided by
Hector Virgen, that does basically what I am proposing (it just needs
refinement) and am just after some feedback on the proposal from the
community.
The proposal is located at:
http://framework.zend.com/wiki/display/ZFPROP/Zend_Db_Table_Mptt+-+Nick+Pac
k
An excellent article on what MPTT is and how you use it is at (for those
of you that have no idea what MPTT is!):
http://www.sitepoint.com/article/hierarchical-data-database/
I have a couple of questions with regards to its design that I would
like some feedback on.
1. Should the top level parent node have parent_id values of 0 or NULL,
from a normalisation perspective, one would guess that the parent should
be 0 so that all values in the col are of the same type, however by
using 0 you are effectively creating a reference to a non-existant row -
any feedback on this behavior would be greatly appreciated
If we're talking DB, you must use null to comply to DB FK restrictions. If
we're talking code, 0 is fine.
2. This question is with regards to handling deletion of nodes that have
children, it would seem much more sensible to move the child nodes of
the deleted node up to the grandparent node, rather than breaking the
chain of parent references or deleting the child nodes completely, is
this the best way to approach it?
You can mimick the FK behavior: MAKE NULL, RESTRICT and CASCADE. I'd add
REATTACH here and you should be set.
like this:
// make all direct children root nodes, retaining their subtrees
$table->delete($id, Zend_Db_Table_Mptt::DELETE_MAKE_NULL);
// restrict deleting if child nodes exists
if ($table->delete($id, Zend_Db_Table_Mptt::DELETE_RESTRICT)) {
// delete successful
} else {
// delete failed
}
// delete the node and all it's child nodes recursively
$table->delete($id, Zend_Db_Table_Mptt::DELETE_CASCADE);
// attach all nodes direct children to it's parent, making them siblings
$table->delete($id, Zend_Db_Table_Mptt::DELETE_REATTAC);
// attach all nodes direct children to node with ID $newParent
$table->delete($id, Zend_Db_Table_Mptt::DELETE_REATTACH, $newParent);
These are all just examples, but you should get the gist. :)
