How to Build an Unordered List Menu Tree in PHP/MySQL Without Recursion?

PHP/MySQL Unordered List Menu Tree Construction: A Non-Recursive Single Database Query Approach

Building unordered list menu trees from database queries is a common task. Typically, recursive functions that query the database multiple times are employed. However, a more efficient non-recursive approach is possible using a single database query.

Given an array of page objects with id, title, and parent_id attributes, the goal is to create a function that generates the HTML for an unordered list menu.

Solution:

Our solution employs the following steps:

1. Create a helper function, has_children, to determine if a given parent_id has any children in the array.
2. Implement a build_menu function that iterates through the page objects and constructs the menu list recursively.
3. Call build_menu with the initial parent ID of 0 to create the root of the menu tree.

Code:

<code class="php">function has_children($rows, $id) {
  foreach ($rows as $row) {
    if ($row['parent_id'] == $id){
      return true;
    }
  }
  return false;
}

function build_menu($rows, $parent=0) {
  $result = "<ul>";
  foreach ($rows as $row) {
    if ($row['parent_id'] == $parent){
      $result.= "<li>{$row['title']}";
      if (has_children($rows,$row['id'])) {
        $result.= build_menu($rows,$row['id']);
      }
      $result.= "</li>";
    }
  }
  $result.= "</ul>";

  return $result;
}</code>

Example Usage:

<code class="php">$menu = [
  ['id' => 1, 'title' => 'Menu 1', 'parent_id' => null],
  ... // Additional menu objects
];

echo build_menu($menu); // Outputs the complete menu list</code>

Advantages:

• Non-recursive approach eliminates the risk of stack overflow.
• Single database query ensures efficient data retrieval.
• Modular design facilitates maintainability and reusability.

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