Somewhat-Hierarchical Data With MySQL - php

Question

I'm working with some somewhat hierarchical data for a work project and trying to find a more efficient way of dealing with it as my first attempt is probably dreadful in more ways than one. I've looked at a number of hierarchical data questions on this site so I know that with my structure it's nigh-impossible to get the information in a single query.
The table I'm querying from is on an AS/400 and each entry stores a single part of a single step, so if I had PartOne and three Components go into it there is an entry for each like:
PartOne ComponentOne, PartOne ComponentTwo, PartThree ComponentThree.
Its important to note if there are components for ComponentOne a subsequent row could contain:
ComponentOne SubComponentOne, ComponentOne SubComponentTwo.
With this in mind I'm trying to get all of the components in a tree-like structure for given finished parts, basically getting everything that goes into the final product.
I cannot create a flattened table for this, as what I'm trying to do is dynamically generate that flattened table. I do however have access to the list of finished parts. So my current algorithm goes like this
Fetch part number, query table for the components when that's the created part.
Take those components and query for each as the created part and get their components.
Repeat until query returns no entries.
In this case that's 7 queries deep. I'm wondering from anyone on the outside looking in if a better algorithm makes sense for this and also its been a while since I've done recursion but this seems reasonable for recursion at least in the creation of the queries. Would it be reasonable to look into creating a recursive function that passes back the query results from each level and somewhere in there store the information in an array/table/database entries?

Answer 1

Do you want a tree structure in php?
Then the next code sample might be interesting.
This builds a tree for records in the categories table starting with id -1000 as the root element, using only as many queries as the number of levels deep you want the information.
Table structure:
TABLE categories (
id INT NOT NULL PRIMARY KEY,
parent_id INT NULL,
name NVARCHAR(40) NOT NULL
)
PHP code:
class Bom {
public $Id;
public $Name;
public $Components = array();
function __construct( $id, $name ) {
$this->Id = $id;
$this->Name = $name;
}
}
$parentIds = array( -1000 ); // List of id's to lookup
$rootBom = new Bom( -1000, 'Root' );
$bomsById[ -1000 ][] = $rootBom; // For each id there can be multiple instances if we want separate instances of Bom for each time it occurs in the tree
$maxLevel = 0;
while ( count( $parentIds ) > 0
&& $maxLevel++ < 10
&& $result = $mysqli->query( "SELECT * FROM categories WHERE parent_id IN ( " . implode( ", ", $parentIds ) . " ) ORDER BY name" ) )
{
$parentIds = array(); // Clear the lookup list
$newBomsById = array();
while ( $row = $result->fetch_assoc() )
{
$boms = $bomsById[ $row[ 'parent_id' ] ];
if ( $boms )
{
foreach ( $boms as $bomToUpdate )
{
$compontentBom = new Bom( $row[ 'id' ], $row[ 'name' ] );
$bomToUpdate->Components[] = $compontentBom;
$newBomsById[ $compontentBom->Id ][] = $compontentBom;
}
$parentIds[] = $row[ 'id' ]; // Build new list of id's to lookup
}
}
$bomsById = $newBomsById;
}
echo '<!--
' . print_r( $rootBom, true ) . '
-->';