Question

我有这样的文件结构：

{
  favourite_shops: [
    {
      shop_id: "5961352278cba91cc6a6e8cc",
      time: "2017-07-11T14:43:35.465Z"
    },
    {
      shop_id: "5964e446c15c760f9b646d99",
      time: "2017-07-11T14:44:40.429Z"
    },
    {
      shop_id: "5964e446c15c760f9b646d98",
      time: "2017-07-11T14:44:50.988Z"
    }
  ]
}

我怎样才能将其转换为这样的东西：

{
  favourite_shops: [
    "5961352278cba91cc6a6e8cc",
    "5964e446c15c760f9b646d99",
    "5964e446c15c760f9b646d98" 
  ]
}

Answer 1

假设我们有这样的数据结构：

icon_img = cv2.imread("icon.png")
icon_img1= cv2.resize(icon_img, (20,20))
x_offset=y_offset=5
img[y_offset:y_offset+icon_img1.shape[0], x_offset:x_offset+icon_img1.shape[1]] = icon_img1

cv2.putText(img, "my_text", (x_offset+icon_img1.shape[1], y_offset+icon_img1.shape[0]), font, 1.0, (255, 255, 255), 0)

只是一点 ES6魔法：

const data = {
  favourite_shops: [
    {
      shop_id: "5961352278cba91cc6a6e8cc",
      time: "2017-07-11T14:43:35.465Z"
    },
    {
      shop_id: "5964e446c15c760f9b646d99",
      time: "2017-07-11T14:44:40.429Z"
    },
    {
      shop_id: "5964e446c15c760f9b646d98",
      time: "2017-07-11T14:44:50.988Z"
    }
  ]
};

第二种优雅方法：

const result = {
  favourite_shops: []
};

data.favourite_shops.forEach(el => result.favourite_shops.push(el.shop_id));

Answer 2

您可以在阵列本身$map上获取所需的字段。（这在查询本身内完成，而不是在收到文件后）

例如

给出文件;

> db.Shopping.find().pretty()
{
    "_id" : ObjectId("59651ce38828356e1a39fde9"),
    "favourite_shops" : [
        {
            "shop_id" : "5961352278cba91cc6a6e8cc",
            "time" : "2017-07-11T14:43:35.465Z"
        },
        {
            "shop_id" : "5964e446c15c760f9b646d99",
            "time" : "2017-07-11T14:44:40.429Z"
        },
        {
            "shop_id" : "5964e446c15c760f9b646d98",
            "time" : "2017-07-11T14:44:50.988Z"
        }
    ]
}
{
    "_id" : ObjectId("59665cf3d8145b41e5d2f5da"),
    "favourite_shops" : [
        {
            "shop_id" : "2222",
            "time" : "2017-07-11T14:43:35.465Z"
        },
        {
            "shop_id" : "4444",
            "time" : "2017-07-11T14:44:40.429Z"
        },
        {
            "shop_id" : "6666",
            "time" : "2017-07-11T14:44:50.988Z"
        }
    ]
}

$map数组上的

favourite_shops {$match}阻止是可选的，如果您想要所有文档的购物ID，则可以删除

> db.Shopping.aggregate([[
  {
    "$match": {
      "_id": ObjectId("59651ce38828356e1a39fde9")
    }
  },
  {
    "$project": {
      "my_favourite_shops": {
        "$map": {
          "input": "$favourite_shops",
          "as": "each_shop",
          "in": "$$each_shop.shop_id"
        }
      }
    }
  }
]).pretty()
{
    "_id" : ObjectId("59651ce38828356e1a39fde9"),
    "my_favourite_shops" : [
        "5961352278cba91cc6a6e8cc",
        "5964e446c15c760f9b646d99",
        "5964e446c15c760f9b646d98"
    ]
}

而且，使用mongodb 3.4.4，我只能在嵌套字段上$project，

db.Shopping.aggregate([{"$project": {"my_favourite_shops": "$favourite_shops.shop_id"}}]).pretty()
{
    "_id" : ObjectId("59651ce38828356e1a39fde9"),
    "my_favourite_shops" : [
        "5961352278cba91cc6a6e8cc",
        "5964e446c15c760f9b646d99",
        "5964e446c15c760f9b646d98"
    ]
}
{
    "_id" : ObjectId("59665cf3d8145b41e5d2f5da"),
    "my_favourite_shops" : [
        "2222",
        "4444",
        "6666"
    ]
}

将mongodb数组文档转换为单个字段

2 个答案: