Prepending an unknown amount of database fields to array - arrays

Question

I have a database with the following structure
user_id | cat_name | cat_slug | parent_id
-------------------------------------------
Tools | tools | 0 |
2 |Chainsaws |chainsaws | 1
etc
My end goal is to essentially have an array that has a breadcrumb trail of sorts that shows the category path, it could have anywhere from no parents to 5 levels of category parenting.
I was able to kind of get what I want.. with a few errors along the way. I keep getting a Trying to get property of non-object error. Althrough all my other attempts at returning values have failed.
My solution outputs my (semi - desired) effect underneath the errors, and with additional category breaks ( symbolized by ">" ). I was just hoping someone could help me clean it up, because I'm at a breaking point, after going about this for a few hours with no solution.
Model
function get_parent_trail($parent_id){
if ( $parent_id != 0 && $parent_id){
$parent_trail = array();
for( $i = 1; $i <= 4; $i ++ ) {
$this -> db -> select ( '*' );
$this -> db -> from ( 'categories' );
$this -> db -> where ( 'cat_id' , $parent_id );
$query = $this -> db -> get() -> row();
array_unshift( $parent_trail, $query->cat_name ) ;
$parent_id = $query->parents;
}
foreach( $parent_trail as $ti ) {
if ( $ti ) {
echo "<strong>" . $ti . "</strong> > ";
}
}
} else {
echo "<span style='color:red;'>No Parent Category</span>";
}
}
View
<table class='admin_table'>
<thead>
<th>ID</th>
<th>Name</th>
<th>Parent</th>
</thead>
<tbody>
<?php
foreach($cats as $cat){
echo "<tr>";
echo "<td>" . $cat['cat_id'] . "</td>";
echo "<td>" . $cat['cat_name'] . "</td>";
echo "<td>";
$this -> categories -> get_parent_trail( $cat['parents'] );
echo "</td>";
echo "</tr>";
}
?>
</tbody>
</table>
NOTE:
The '4' in the for loop doesn't need to be dynamic as I've set a hard limit of up to 5 categories, though there has been no need to go that far into sub-categories.
I also have an additional ">" at the end of my list, which I need to get rid of, I know the reason my way doesn't work, it's just the closest solution I could find for the time being.
End Result
Basically, I want my end result to look like;
With 2 'levels' of parent categories
id | name | slug | Parent(s)
-----------------------------------------------------------------------
1 | Electric Chainsaws | electric-chainsaws | Tools > Chainsaws

Answer 1

What you are wanting to do is build a recursive function.
Example of this would be:
function factorial($number)
{
if ($number < 2)
{
return 1;
}
else
{
return ($number * factorial($number-1));
}
}

Answer 2

After much hair pulling and several bottles of very strong rum, I was able to finally figure this out. I'm still relatively novice at using codeigniter so my solution may have some unnecessary steps to it, but I feel obliged to share what I learned. Here is my entire function.
function get_parent_trail($parent_id){
if ( $parent_id != 0 && $parent_id){
$parent_trail = array();
$inc = 0;
for( $i = 1; $i <= 4; $i ++ ) {
if ( $parent_id != 0 && $parent_id){
$this -> db -> select ( '*' );
$this -> db -> from ( 'categories' );
$this -> db -> where ( 'cat_id' , $parent_id );
$query = $this -> db -> get();
$row = $query -> row_array();
array_unshift( $parent_trail, $row['cat_name'] ) ;
$parent_id = $row['parents'];
} else {
$inc++;
}
}
$popOff = array_pop($parent_trail);
if ($inc > 2 ){
echo "<span style='color:red;'>No Parent Category</span>";
}
$string = '';
foreach( $parent_trail as $ti ) {
if ( $ti ) {
$string .= $ti.' > ';
}
}
(string) $test = substr($string, 0, -2);
echo $test;
} else {
echo "<span style='color:red;'>No Parent Category</span>";
}
}