如何在Laravel中从同一张表创建多级分类树

Schema::create('categories', function (Blueprint $table) {
    $table->id();
    $table->string('name');
    $table->unsignedBigInteger('parent_id')->nullable();
    $table->timestamps();

    $table->foreign('parent_id')->references('id')->on('categories')->onDelete('cascade');
});

class Category extends Model
{
    public function parent()
    {
        return $this->belongsTo(Category::class, 'parent_id');
    }

    public function children()
    {
        return $this->hasMany(Category::class, 'parent_id');
    }
}

function buildCategoryTree($categories, $parentId = null)
{
    $branch = [];

    foreach ($categories as $category) {
        if ($category->parent_id == $parentId) {
            $children = buildCategoryTree($categories, $category->id);
            if ($children) {
                $category->children = $children;
            }
            $branch[] = $category;
        }
    }

    return $branch;
}

// 使用示例
$categories = Category::all();
$tree = buildCategoryTree($categories);