Category Hierarchy (PHP/MySQL)

Question

I am trying to get my all categories and sub-categories from MySQL database in a hierarchy:

My result should be like that (just example):

Answer 1

Try the following code

//connect to mysql and select db

$conn = mysqli_connect('localhost', 'user', 'password','database');

if( !empty($conn->connect_errno)) die("Error " . mysqli_error($conn));

//call the recursive function to print category listing
category_tree(0);

//Recursive php function
function category_tree($catid){
global $conn;

$sql = "select * from category where parent_id ='".$catid."'";
$result = $conn->query($sql);

while($row = mysqli_fetch_object($result)):
$i = 0;
if ($i == 0) echo '<ul>';
 echo '<li>' . $row->cat_name;
 category_tree($row->id);
 echo '</li>';
$i++;
 if ($i > 0) echo '</ul>';
endwhile;
}
//close the connection
mysqli_close($conn);
?>

More...

Answer 2

I have a new idea I think it will be nice. The idea is this: in category_parent column we will insert a reference to all parents of this node.

+----+----------------------+-----------------+
| id | category_name        |    hierarchy    |
+----+----------------------+-----------------+
| 1  | cat1                 |        1        |
+----+----------------------+-----------------+
| 2  | cat2                 |        2        |
+----+----------------------+-----------------+
| 3  | cat3                 |        3        |
+----+----------------------+-----------------+
| 4  | subcat1_1            |       1-4       |
+----+----------------------+-----------------+
| 5  | subcat1_2            |       1-5       |
+----+----------------------+-----------------+
| 6  | subsubcat1_1         |      1-4-6      |
+----+----------------------+-----------------+
| 7  | subsubcat1_2         |      1-4-7      |
+----+----------------------+-----------------+
| 8  | subsubcat1_3         |      1-4-8      |
+----+----------------------+-----------------+
| 9  | subsubcat1_3_1       |     1-4-8-9     |
+----+----------------------+-----------------+
| 10 | subsubcat1_3_2       |     1-4-8-10    |
+----+----------------------+-----------------+
| 11 | subsubcat1_3_1_1     |    1-4-8-9-11   |
+----+----------------------+-----------------+
| 12 | subsubsubcat1_3_1_1  |   1-4-8-9-12    |
+----+----------------------+-----------------+
| 13 | subsubsubcat1_3_1_2  |  1-4-8-9-11-13  |
+----+----------------------+-----------------+
| 14 | subsubsubcat1_2_1_3  |  1-4-8-9-11-14  |
+----+----------------------+-----------------+

if you look at my updated table you will notice that every record has an link to its parents, not only the direct one, But also all of parents. And for that job I made some modification to insert to be:

Insert into table_name (category_name, hierarchy) values ('new_name', (concat(parent_hierarch, '-', (SELECT Auto_increment FROM information_schema.tables WHERE table_name='table_name'))))

Now lets make your desired queries:

1- all sub categories of cars:

select * from table_name where hierarchy like '1-%'

2- if you need all parent of BLACK you simply type:

select * from table_name where hierarchy = '1-4-8-9' or hierarchy = '1-4-8' or hierarchy = '1-4' or hierarchy = '1'

(you can build that query from php, splitting hierarchy field at '-' char)

3- To see all categories, with level and direct parent:

select *, SUBSTR(hierarchy, 1, (LENGTH(hierarchy) - LENGTH(id) - 1)) as parent, LENGTH(hierarchy) - LENGTH(REPLACE(hierarchy, '-', '')) as level From table_name

+----+----------------------+-----------------+-----------+--------+
| id | category name        |    hierarchy    |   parent  |  level |
+----+----------------------+-----------------+-----------+--------+
| 1  | cat1                 |        1        |           |    0   |
+----+----------------------+-----------------+-----------+--------+
| 2  | cat2                 |        2        |           |    0   |
+----+----------------------+-----------------+-----------+--------+
| 3  | cat3                 |        3        |           |    0   |
+----+----------------------+-----------------+-----------+--------+
| 4  | subcat1_1            |       1-4       |     1     |    1   |
+----+----------------------+-----------------+-----------+--------+
| 5  | subcat1_2            |       1-5       |     1     |    1   |
+----+----------------------+-----------------+-----------+--------+
| 6  | subsubcat1_1         |      1-4-6      |    1-4    |    2   |
+----+----------------------+-----------------+-----------+--------+
| 7  | subsubcat1_2         |      1-4-7      |    1-4    |    2   |
+----+----------------------+-----------------+-----------+--------+
| 8  | subsubcat1_3         |      1-4-8      |    1-4    |    2   |
+----+----------------------+-----------------+-----------+--------+
| 9  | subsubcat1_3_1       |     1-4-8-9     |   1-4-8   |    3   |
+----+----------------------+-----------------+-----------+--------+
| 10 | subsubcat1_3_2       |     1-4-8-10    |   1-4-8   |    3   |
+----+----------------------+-----------------+-----------+--------+
| 11 | subsubcat1_3_1_1     |    1-4-8-9-11   |  1-4-8-9  |    4   |
+----+----------------------+-----------------+-----------+--------+
| 12 | subsubsubcat1_3_1_1  |   1-4-8-9-12    |  1-4-8-9  |    4   |
+----+----------------------+-----------------+-----------+--------+
| 13 | subsubsubcat1_3_1_2  |  1-4-8-9-11-13  |1-4-8-9-11 |    5   |
+----+----------------------+-----------------+-----------+--------+
| 14 | subsubsubcat1_2_1_3  |  1-4-8-9-11-14  |1-4-8-9-11 |    5   |
+----+----------------------+-----------------+-----------+--------+

This is a new idea and need some improvement.

Answer 3

When using an adjacency list model, you can generate the structure in one pass.

Taken from One Pass Parent-Child Array Structure (Sep 2007; by Nate Weiner):

$refs = array();
$list = array();

$sql = "SELECT item_id, parent_id, name FROM items ORDER BY name";

/** @var $pdo \PDO */
$result = $pdo->query($sql);

foreach ($result as $row)
{
    $ref = & $refs[$row['item_id']];

    $ref['parent_id'] = $row['parent_id'];
    $ref['name']      = $row['name'];

    if ($row['parent_id'] == 0)
    {
        $list[$row['item_id']] = & $ref;
    }
    else
    {
        $refs[$row['parent_id']]['children'][$row['item_id']] = & $ref;
    }
}

From the linked article, here's a snippet to create a list for output. It is recursive, if there a children for a node, it calls itself again to build up the subtree.

function toUL(array $array)
{
    $html = '<ul>' . PHP_EOL;

    foreach ($array as $value)
    {
        $html .= '<li>' . $value['name'];
        if (!empty($value['children']))
        {
            $html .= toUL($value['children']);
        }
        $html .= '</li>' . PHP_EOL;
    }

    $html .= '</ul>' . PHP_EOL;

    return $html;
}

Related Question:

• How to obtain a nested HTML list from object's array recordset?

Answer 4

There's another way to achieve the same effect which I find a bit easier to follow (without the reference trick). You build the tree by adding the relevant information to the current node and to its parent (assume the foreach iterates over the returned rows from the SQL query):

$tree = array();
foreach ($query->result() as $row)
{
    $pid  = $row->parent_id;
    $id   = $row->id;
    $name = $row->name;

    // Create or add child information to the parent node
    if (isset($tree[$pid]))
        // a node for the parent exists
        // add another child id to this parent
        $tree[$pid]["children"][] = $id;
    else
        // create the first child to this parent
        $tree[$pid] = array("children"=>array($id));

    // Create or add name information for current node
    if (isset($tree[$id]))
        // a node for the id exists:
        // set the name of current node
        $tree[$id]["name"] = $name;
    else
        // create the current node and give it a name
        $tree[$id] = array( "name"=>$name );
}
return $tree;

and to display the tree:

function toUL($tree, $id, $html){
  $html .= '<ul>'.PHP_EOL;

  if (isset($tree[$id]['name']))
    $html .= '<li>' . $tree[$id]['name'];

  if (isset($tree[$id]['children']))
  {
    $arChildren = &$tree[$id]['children'];
    $len = count($arChildren);
    for ($i=0; $i<$len; $i++) {
        $html .= toUL($tree, $arChildren[$i], "");
    }
    $html .= '</li>'.PHP_EOL;
  }

  $html .= '</ul>'.PHP_EOL;
  return $html;
}

// Display the tree
echo toUL($tree, 0, "");

Answer 5

@Amnon Your code works perfectly. Just tested it with CodeIgniter and it worked like a charm. Here's the working code if anyone needs it:

<?php

function disTree($all_cats) {
$tree = array();
foreach ($all_cats as $cat)
{
    $pid  = $cat->parent_id;
    $id   = $cat->cat_id;
    $name = $cat->cat_name;

    // Create or add child information to the parent node
    if (isset($tree[$pid]))
        // a node for the parent exists
        // add another child id to this parent
        $tree[$pid]["children"][] = $id;
    else
        // create the first child to this parent
        $tree[$pid] = array("children"=>array($id));

    // Create or add name information for current node
    if (isset($tree[$id]))
        // a node for the id exists:
        // set the name of current node
        $tree[$id]["name"] = $name;
    else
        // create the current node and give it a name
        $tree[$id] = array( "name"=>$name );
}
return $tree;
}


function toUL($tree, $id, $html){
  $html .= '<ul>'.PHP_EOL;

  if (isset($tree[$id]['name']))
    $html .= '<li>' . $tree[$id]['name'];

  if (isset($tree[$id]['children']))
  {
    $arChildren = &$tree[$id]['children'];
    $len = count($arChildren);
    for ($i=0; $i<$len; $i++) {
        $html .= toUL($tree, $arChildren[$i], "");
    }
    $html .= '</li>'.PHP_EOL;
  }

  $html .= '</ul>'.PHP_EOL;
  return $html;
}

$tree = disTree($all_cats);
// Display the tree
echo toUL($tree, 0, "");

?>

The only thing I changed was adding my own array ($all_cats).