如何 $project ObjectId 到 mongodb 聚合中的字符串值? [英] how to $project ObjectId to string value in mongodb aggregate?

问题描述

是否有我可以在 aggregate 函数中使用的运算符来获取字符串而不是 ObjectId 作为响应?

Is there an operator I could use in aggregate function to get a string instead of ObjectId in response?

db.something.aggregate([
  { "$match": { "property": { "$exists": true } } },
  { "$project": { "stringId": "$_id.???" } }
])

推荐答案

Mongodb 4.0 引入了 $toString 聚合运算符.所以，现在您可以轻松地将 ObjectId 转换为字符串

Mongodb 4.0 has introduced $toString aggregation operator. So, Now you can easily convert ObjectId to string

db.collection.aggregate([
  {
    $project: {
      _id: {
        $toString: "$_id"
      }
    }
  }
])

OR 反之亦然，使用 $toObjectId 聚合

OR vice versa using $toObjectId aggregation

db.collection.aggregate([
  {
    $project: {
      _id: {
        $toObjectId: "$_id"
      }
    }
  }
])

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