Posted by Oli Filth on 09/16/05 21:11

Oli Filth said the following on 16/09/2005 19:10:
> nospam said the following on 16/09/2005 18:55:
>
>> Hi all,
>>
>> I'd like to implement a tree of "tags" for a blog I'm writing for fun
>> in PHP.
>> Here's what a single tag looks like:
>>
>>
>> CREATE TABLE tags
>> ( name varchar(30) not null default '',
>> id_self integer(12) not null primary key,
>> id_parent integer(10) not null default 0,
>> );
>> INSERT INTO tags VALUES ('root of the tree', 0, 0);
>>
>>
>> Each tag has a name, a unique id to identify itself with and a
>> parent's id,
>> and all this will be stored in a database, but stored in no particular
>> order.
>>
>> I'm a little stumped as to how to reconstruct the tree. Part of the
>> problem
>> is that suppose my first read to the database yeilds:
>>
>> name = "physics"
>> id_self = 21
>> id_parent = 2
>>
>>
>> but further down in the database, this record exists:
>>
>> name = "science"
>> id_self = 2
>> id_parent = 0
>>
>> in other words, it's possible that children may be read before parents.
>
>
>
> One simple way round this would be to load each tree element into a flat
> array at first, each element keyed by its own ID. Then loop through
> every element in turn, get its parent's ID, and then call an addChild()
> function or something, e.g:
>
> class Node
> {
> public $id;
> public $parentId;
> public $children;
>
> public function addChild($childObject)
> {
> $children[$childObject->id] = $childObject;
^
Oops, that should be:
$this->children[$childObject->id] = $childObject;
> }
> }
>
> // assume that $flatArray is the array of unconnected Nodes that have
> // been constructed from the database query.
>
> foreach ($node in $flatArray)
> {
> $flatArray[$node->parentId]->addChild($node);
> }
>
>
> (This example assumes you're using PHP 5).
>


--
Oli

[Back to original message]