concat tree hierarchie in a recursive PHP function

Question

I have a user table with hierachical users. So users can have a parent user. I am trying to return an array of all child user ids of a certain user. My function returns "null". What's wrong?

public function userDownline($userid, $result = array()) {
    $dbconn = $this->DBase();
    $children = $dbconn->GetAll('SELECT id FROM users WHERE parent=' . (int)$userid);
    if(count($children) > 0) {
        foreach($children As $k=>$v) {
            if(!in_array($v['id'], $result)) $result[] = $v['id'];
            $this->userDownline($v['id'], $result);
        }
    } else {
        return $result;
    }
}

vuliad · Accepted Answer · 2017-01-22 18:00:11Z

1

Of course it will return null, because you are in block if(count($children)) and there is no return from this.

I think you have to do something like this:

<?php
public function userDownline($userid, &$result = array())
{
    $dbconn = $this->DBase();
    $children = $dbconn->GetAll('SELECT id FROM users WHERE parent=' . (int)$userid);
    if (count($children) > 0) {
        foreach ($children As $k => $v) {
            if (!in_array($v['id'], $result)) $result[] = $v['id'];
            $this->userDownline($v['id'], $result);
        }
    }
    return $result;
}

I added reference in function signature and move return out of the conditional block.

But this is really totaly inefficient way and dangerous(because of - out of memory, too many nesting level and other exceptions).

There are 2 better ways:

Use https://neo4j.com/ - Graph Database - best option for your task.
If you still wanna use only Sql DB - read about Nested set Model http://mikehillyer.com/articles/managing-hierarchical-data-in-mysql/

edited Jan 22, 2017 at 18:00

answered Jan 22, 2017 at 17:03

vuliad

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3 Comments

ESP32 Over a year ago

Thanks - I added a "return" to the said line - now I get the first child (1 recordset, instead of many).

ESP32 Over a year ago

The mikehillyer site is awesome - thank you! +1 for this.

ESP32 Over a year ago

Great - &$result did the trick! Now it's working. Many thanks!

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