[Dbix-class] Representing directory structures

[Len Jaffe]

In my opinion, the best way to model a tree in an RDBMS is to use
Materialized Path.

I found the amount of work involved in each insert/delete of a nested set
to be too great, and adjacency lists (parent pointer) fails to allow for
retrieving all of a tree or subtree with one round-trip to the db.
 Materialized Path does not suffer these drawbacks.

I recall there being a couple of MP modules available for DBI and DBIC.

Len.


On Sun, Apr 7, 2013 at 2:42 PM, Bill Moseley <moseley at hank.org> wrote:

> Anyone using DBIC to represent hierarchal directory (folder) structures?
>
> Essentially just like a file system, except users each have their own
> root.  To add to the complexity, I need to be able to "share" folders and
> all child elements to other users.
>
> My assumption is this would involve a single table where each row can
> represent either a directory entry (e.g. a "file") or a sub-directory that
> references its parent.
>
> Postgresql has "WITH RECURSIVE" which DBIC has no support for (other than
> virtual views):
>
> http://www.postgresql.org/docs/9.2/static/queries-with.html
>
>
> But, Adjacency Lists and Nested Sets are (were?) often discussed as
> solutions for hierarchal data in the database.  I asked on the Pg list ba=
ck
> in 2007:
>
>
> http://postgresql.1045698.n5.nabble.com/Adjacency-List-or-Nested-Sets-to-=
model-file-system-hierarchy-td1876116.html
>
>
> but, so far, I've happily avoided using these approaches of representing
> hierarchal data in the database.
>
>
> BTW -- I have recently written a "tag"-based system (like the familiar
> gmail) which is easy to represent in a highly normalized schema but is a
> fundamentally different approach.
>
>
> --
> Bill Moseley
> moseley at hank.org
>
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