WordPress multi level categories / taxonomy to Tree Array

取得無線級樹狀分類
我相信物件導向是Wordpress未來發展方向，所以本文使用 Class WP_Term_Query 取得所有分類，而不是使用 get_terms 方法，代碼如下：

$args = array(
  'taxonomy' => 'category',
  'orderby' => 'name',
  'order' => 'ASC',
  'hierarchical'  => true,
  'hide_empty' => false,
);
$the_query = new WP_Term_Query($args);
$categories = $the_query->get_terms();

會返回 WP_Term 物件陣列，結構如下：

Array{
  [0] => WP_Term Object
    (
      [term_id] => 37
      [name] => 天南地北
      [slug] => chat
      [term_group] => 0
      [term_taxonomy_id] => 37
      [taxonomy] => category
      [description] => 
      [parent] => 35
      [count] => 0
      [filter] => raw
    )

  [1] => WP_Term Object
    (
      [term_id] => 35
      [name] => 服務專區
      [slug] => service
      [term_group] => 0
      [term_taxonomy_id] => 35
      [taxonomy] => category
      [description] => 
      [parent] => 0
      [count] => 0
      [filter] => raw
    )
}

為了讓之後選單可以判斷目前層數，以方便縮排…等動作，所以這邊透過 get_ancestors() 取得目前分類的祖先層級，並用count()計算深度，最後再建立這兩個物件成員，以利之後判斷

foreach($categories as $category){
  $ancestors = get_ancestors( $category->term_id, 'category' );
  $category->ancestors = $ancestors; // array( 0 => 15, 1 => 45 ) - 3rd level term
  $category->depth = count( $ancestors ) ;
}

目前 Class WP_Term_Query 似乎沒有沒有相關方法處理無限級菜單資料，所以我們透過 get_cat_tree 這個方法，用遞迴的方式返回菜單的巢狀的陣列資料，陣列的值仍然是WP_Term 物件。

function get_cat_tree($parent,$categories) {
    $result = array();
    foreach($categories as $category){
        if ($parent == $category->parent) {
            $category->children = get_cat_tree($category->term_id,$categories);
            $result[] = $category;
        }
    }
    return $result;
}
$cats_tree = get_cat_tree(0,$categories);