在MongoDB中获取特定级别嵌套文档的最有效方法

考虑到以下结构：

      {
      "name": "CatA",
      "subcategories" : [
         {
         "name" : "SubCatA",
         "subcategories" : [
            {
            "name" : "SubSubCatA",
            "subcategories" : [
                {
                "name" : "SubSubSubCatA",
                "subcategories" : [
                ]
            }
         ]}]}]}

获取所有子类别（例如，级别3）的最佳方法是什么

这项工作：

    db.Categories.aggregate(
        {$unwind: '$subcategories'},
        {$unwind: '$subcategories.subcategories'},
        {$unwind: '$subcategories.subcategories.subcategories'},
        {$project : { subcategories : "$subcategories.subcategories.subcategories" }}
    )

这是最有效的方法吗