Create Hierarchical Array from MySQL result - php

Question

I've seen other questions about this but not quite like my situation. I have the following table in MySQL:
term_id name slug taxonomy parent
1 Entry Form entry-form format 0
2 Page page format 3
3 Facebook facebook format 0
4 Entry Form facebook-entry-form format 3
5 Twitter twitter format 0
6 Single single format 2
I have the following OBJECT query:
$formats = $wpdb->get_results($wpdb->prepare("
SELECT * FROM table t
WHERE t.taxonomy = 'format'
"));
I wind up with the following array:
Array ( [0] => stdClass Object ( [term_id] => 1 [name] => Entry Form [slug] => entry-form [taxonomy] => format [parent] => 0 ) [2] => stdClass Object ( [term_id] => 2 [name] => Page [slug] => page [taxonomy] => format [parent] => 3 ) [3] => stdClass Object ( [term_id] => 3 [name] => Facebook [slug] => facebook [taxonomy] => format [parent] => 0 ) [4] => stdClass Object ( [term_id] => 4 [name] => Entry Form [slug] => entry-form-facebook [taxonomy] => format [parent] => 3 ) [5] => stdClass Object ( [term_id] => 5 [name] => Twitter [slug] => twitter [taxonomy] => format [parent] => 0 ) [6] => stdClass Object ( [term_id] => 6 [name] => Single [slug] => single [taxonomy] => format [parent] => 2 ) ) 1
All of the above needs to be turned into a hierarchical list on output that looks like this:
Entry Form
Twitter
Facebook
- Entry Form
- Page
-- Single
As such, I need to turn array $formats into a hierarchical array based on the parent field. A parent of 0 means it is a top level item. As such, since Single has parent of 2 it is the child of Page which in turn has parent of 3 and is a child of Facebook.
Can anyone help me turn my array into a hierarchical array and then show me how I can loop through it for output?

Answer 1

If performance due to volume of queries is not going to be a problem, the simplest solution is that, instead of doing a single query that populates an array, you do one query per node in your hierarchical tree, adding a "AND parent = $id", where $id is the term_id of the current node. Something like:
Do a SELECT WHERE .... AND parent = 0;
for each result in 1, $id = term_id, do a select WHERE ... AND
parent = $id
Repeat recursively until no more results
If performance is a problem you can still dump the query to your array and apply the same algorithm to the array, but you most likely will have memory issues doing it that way if you really have that much volume.

Answer 2

You need to put the data into assoc array while fetching it from the database:
//$groups - result array
$groups = array();
//$record contains the assoc array of the current record
while($record = $result->fetchAssoc()) {
if (!isset($groups[$record["parent"]]))
{
$groups[$record["parent"]] = array();
}
array_push($groups[$record["parent"]], $record);
}
In the end you will get an assoc array of hierarchy with parent as a key. Then traverse through it recursively, and you'll get the result:
function print_recursively(&$groups, $parent_id, $dashes = '')
{
if(isset($groups[$parent_id]))
{
foreach($groups[$parent_id] as $key => $value)
{
print $dashes . ' ' . $value["name"];
print_recursively(&$groups, $value["term_id"], $dashes . '-');
}
}
}
I didn't test this code, but the algorithm is correct.