How to Recursively Build a Multidimensional Array from a Flat Database Result?

Recursive Function to Construct Multidimensional Array from Database Result

Problem:

You seek a recursive function capable of transforming an array of pages and categories from a flattened database result into a nested array with structured hierarchical relationships.

Solution:

The provided solution offers a straightforward and generic approach:

function buildTree(array $elements, $parentId = 0) {
    $branch = array();

    foreach ($elements as $element) {
        if ($element['parent_id'] == $parentId) {
            $children = buildTree($elements, $element['id']);
            if ($children) {
                $element['children'] = $children;
            }
            $branch[] = $element;
        }
    }

    return $branch;
}

Explanation:

The algorithm operates as follows:

1. Initial Execution (ParentId = 0):

   • Considers the entire array of elements.
   • Identifies elements with parent_id equal to 0 (root nodes).
   • Recursively calls buildTree on those elements to find their children.

2. Recursive Execution (ParentId != 0):

   • Considers only the elements that match the specified parent_id.
   • Recursively calls buildTree on those elements to find their children.

3. Building the Hierarchy:

   • Elements identified as children of the current parent are incorporated into an array.
   • This array is assigned to the "children" property of the parent element.

4. Return Result:

   • The recursive calls return arrays of child elements for each level of the hierarchy.
   • The function culminates by returning a complete nested array representing the hierarchical structure.

By applying this function to your database result, you obtain an organized array with granular hierarchical relationships, as exemplified by your desired output. This approach is versatile and can be applied to both pages and categories.

The above is the detailed content of How to Recursively Build a Multidimensional Array from a Flat Database Result?. For more information, please follow other related articles on the PHP Chinese website!