Root should have left and right value, and a parentID of null or 0
depending on implementation.
On 27 Jul 2009, at 21:26, Ali <[email protected]> wrote:
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. :)
