PHP recursive function to delete all child nodes causes stackoverflow

Question

My MySQL looks like this: (the name of the table is category)

'id', 'content', 'parent'

where:

id = the id of the category
content = some-text-we-dont-care-about
parent = the id of the parent category

this is what I'm trying right now:

function remrecurs($id) {
    $qlist=mysql_query("SELECT * FROM category WHERE parent='$id'");
    if (mysql_num_rows($qlist)>0) {
         while($curitem=mysql_fetch_array($qlist)) {
              remrecurs($curitem['parent']);
         }
    }
    mysql_query("DELETE FROM category WHERE id='$id'");
}

Which for some reason doesnt work and crashes .. Any idea what I'm doing wrong ?

codaddict · Accepted Answer · 2010-10-21 09:20:47Z

11

The problem is in the recursive call:

remrecurs($curitem['parent']);

it should be:

remrecurs($curitem['id']);

Why?

Your objective is to delete the row with given id. First you check to see if it has any children. If yes you need to call the recursive delete on each of the children not on the parent again. You are calling the function recursively on the parent again..this leads to infinite recursive calls, you thrash the stack and crash.

answered Oct 21, 2010 at 9:20

codaddict

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1 Comment

DreamWave Over a year ago

thank you! works great now - I hate it when things like that slow me down - I guess one needs another point of view on some things :)

Wrikken · Accepted Answer · 2010-10-21 10:59:41Z

5

Alternatively, you could let the database handle this. In MySQL, an InnoDB ON DELETE CASCADE will do this automatically.

CREATE TABLE category (
    id INT PRIMARY KEY AUTO_INCREMENT,
    parent_id INT NULL,
    FOREIGN KEY (parent_id) REFERENCES category (id) ON DELETE CASCADE
) ENGINE=InnoDB

Root nodes should have NULL as parent (not 0 as some people seem to employ on Adjancency List tables).

answered Oct 21, 2010 at 10:59

Wrikken

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