How can I use recursion to retrieve parent nodes? - php

Question

I have created a recursive function to get parent products of a product. I'm almost sure I'm nearly there, but need help snapping out of recursion.
The result I am looking for is something like:
Product 1 (id:1, parent:none)
Product 2 (id:2, parent:1)
--- --- Product 3 (id:3, parent:2)
--- --- Product 4 (id:4, parent:2)
--- Product 5 (id:5, parent:1)
--- --- Product 6 (id:6, parent:5)
--- --- Product 7 (id:7, parent:5)
My updated function is as follows:
function get_parents ($pid, $found = array()) {
array_push ($found, $pid);
$sql = "SELECT * FROM products WHERE child_id = '$pid'";
$result = mysql_query($sql) or die ($sql);
if(mysql_num_rows($result)){
while($row = mysql_fetch_assoc($result)){
$found[] = get_parents($row['pid'], $found);
}
}
return $found;
}
I call it using a simple:
$parents = get_parents($pid);
The problem I am having is that when I run it, it creates an infinite loop, which doesn't break.
I don't want to get done for spamming so I have saved the result of my array to a text file, which can be seen here http://vasa.co/array.txt
Any help would be seriously appreciated :-)

Answer 1

Hmm.. judging by your structure of your DB, it would seem that something is amiss unless I'm missing something
The statement
$sql = "SELECT * FROM products WHERE child_id = '$pid'";
Tells me that for each product, you are storing the ID of the child. Typically, in a tree based structure, it's the reverse, you store the parent ID not the child - unless you want a child node to have many parents. If that is the case, then the function could easily run into problems. Consider the following:
| ID | Child_ID |
+----+----------+
| 1 | 2 |
| 2 | 1 |
This would cause an infinite loop. If you store the parent_id, then by that nature, you are encoding the graph to be hierarchical. Since every product has A parent, then the logic can be written recursively.
The could then be written as such?
function get_parents ($pid, $found = array()) {
array_push ($found, $pid);
$sql = "SELECT * FROM products WHERE id = '$pid'";
$result = mysql_query($sql) or die ($sql);
if(mysql_num_rows($result)){
while($row = mysql_fetch_assoc($result)){
$found[] = get_parents($row['parent_id'], $found);
}
}
return $found;
}