如何访问 MongoDB 中的嵌套数组？

Question

我在 MongoDB 中有一个名为 Product 的文档。产品有一个类别数组，类别有一个子类别数组。

我正在尝试完成两件我遇到困难的事情。 1：检索给定产品ID的类别[]。例如：

• products/10/categories -> categories[]

2：检索给定产品 ID 和类别 ID 的子类别[]。例如：

• products/10/categories/11/subcategories -> 子类别[]

我的架构如下：

Products : [
{
    "id": "productId",
    "name": "productName",
    "price": "productPrice",
    "Categories": [
        {
            "_id": "catId",
            "name": "catName",
            "Subcategories": [
                {
                    "_id": "subcatId",
                    "name": "subcatName"
                },
                {
                    "_id": "subcatId",
                    "name": "subcatName"
                },
            ]
        },
        {
            "_id": "catId",
            "name": "catName",
            "Subcategories": [
                {
                    "_id": "subcatId",
                    "name": "subcatName"
                },
                {
                    "_id": "subcatId",
                    "name": "subcatName"
                },
            ]
        }
    ]
}

]

任何帮助将不胜感激！谢谢！

Answer 1

对于你的第一个问题，你可以这样写查询

db.collection.aggregate([
  {
    $match: {
      "id": "productId"
    }
  },
  {
    $unwind: "$Categories"
  },
  {
    $project: {
      "_id": "$Categories._id",
      "name": "$Categories.name"
    }
  }
])

对于您的第二个查询，请执行此操作

db.collection.aggregate([
  {
    $match: {
      "id": "productId"
    }
  },
  {
    $unwind: "$Categories"
  },
  {
    $match: {
      "Categories._id": "catId"
    }
  },
  {
    $unwind: "$Categories.Subcategories"
  },
  {
    $project: {
      _id: "$Categories.Subcategories._id",
      name: "$Categories.Subcategories.name"
    }
  }
])