Re: celko nested set functions -- tree move

Hi Robert;

The math actually works either way; if it goes negative, the offset is
positive, which is okay. Your selects are way more elegant. I guess I
was just raising the point that using a key other than lft (which tends
to move around in an active tree), is probably safer. The table lock
just keeps the lft and rgt values static while the two updates are
done. If I combined the two updates, I could probably loose the lock;
I took the conservative route.

The node list is around 10k, though using the universe id and tree id
to separate trees, I try to keep trees to around 2k or thereabouts so
that tree manip functions remain reasonably fast. I've found that a
vacuum full analyze is needed at least once a day. Looking over the
tree, I don't see too many nodes that are indented further than ten
levels, although some are as deep as 20. I really like Celko's model
for this app; it makes navigation a snap. Modifying the core functions
to deal with sub-trees, however, was a logic nightmare for my feeble
brain.

Got it on the INTO clause; tks for the tip. I know I have work to do
to tighten up the core code in various places.

The schema's quite large; I'll post it somewhere soon.

Martin

> I think you should take a closer look at Greg's function. It is uses
> lfts as parameters in the function mainly just to make the function
> implementation independent; I was able to easily adapt it to my schema
> which uses unique id's for each object in the tree hierarchy.
>
> After looking your function over, I also have some concerns about moving
> children to new parents with lft and rgt smaller than the child, because
> the math is different depending on which way your moving in the tree.
> It's possible that your use of treeid's and universe id's makes up for
> this, though it's a little hard to discern without seeing the schema,
> perhaps you can post schema and some test data?
>
> I'm also curious how many nodes you have in your tree, and at how many
> levels. It seems like your function would have performance issues over
> large trees since it requires 3 select statements, 3 updates, and a lock
> table. Compare this with Greg's function which requires 2 selects and 1
> update, with no lock.
>
> As a final note, you might want to rewrite your select statements like:
> SELECT
> rgt, universeid, treeid
> FROM
> list_objects
> WHERE
> objid_auto=t_newparent
> INTO
> newparentrgt, newparentuid, newparenttid;
>
> I think it's more readable and probably a little more efficient since
> you are doing less variable assignment.
>
> Robert Treat
>
> On Tue, 2002-11-26 at 00:13, Martin Crundall wrote:
>> I'm not sure that keying off lft is safe in a multi-user environment.
>> I opted to create and use an objid on the tree definition table, since
>> its identity is static. I also found that when trees get active,
>> allowing for tree IDs increased operation speed quite a bit (i
>> actually push this to two levels--a 'universe id' and then a 'tree
>> id'). Here's my version. Clearly not as elegantly written, but
>> nothing's gone awry yet.
>>
>> --
>> ---------------------------------------------------------------------------
>> -- Title: trackmyproject_tree_move()
>> -- Function: moves a tree branch in the hierarchy from one parent to
>> -- another.
>> -- parms: srcobj the branch/object to be moved
>> -- newparent the new parent for the object to be moved --
>> Returns: zero
>> --
>> ---------------------------------------------------------------------------