在MongoDB文档子文档数组中插入并返回子文档ID [英] Insert and return ID of sub-document in MongoDB document sub-document array

问题描述

我的node.js应用会在下面MongoDB文档的嵌套子文档数组字段中插入一个子文档，我需要确定新插入的子文档的ID:

My node.js application will insert a sub-document into a nested sub-document array field of the following MongoDB document, and I need to determine the ID of the newly inserted sub-document:

{
  "_id" : ObjectId("578d5a52cc13117022e09def"),
  "name" : "Grade 5 - Section A",
  "scores" : [{
    "studentId" : ObjectId("5776bd36ffc8227405d364d2"),
    "performance" : [{
      "_id" : ObjectId("57969b8fc164a21c20698261"),
      "subjectId" : ObjectId("577694ecbf6f3a781759c54a"),
      "score" : 86,
      "maximum" : 100,
      "grade" : "B+"
    }]
  }]
}

子文档如下所示:

{
  "subjectId" : ObjectId("5776ffe1804540e29c602a62"),
  "score" : 74,
  "maximum" : 100,
  "grade" : "A-"
}

我正在使用以下 Mongoose 代码添加子文档:

I am adding the sub-document using the following Mongoose code:

Class.update({
  _id: '578d5a52cc13117022e09def',
  'scores.studentId': '5776bd36ffc8227405d364d2'
}, {
  $addToSet: {
    'scores.$.performance': {
      'subjectId' : '5776ffe1804540e29c602a62',
      'score' : 74,
      'maximum' : 100,
      'grade' : 'A-'
    }
  }
}, function(err, result) {
  if (err) {
    throw err;
  }
  console.log(result);
});

subject 子文档被添加到 performance 子文档数组中，该数组本身嵌套在 scores 子文档数组中.请注意，新插入的子文档被分配了自己的 ID，由定义的模式建立.即使我取回整个文档，这也不是很有帮助.我特别需要新插入的子文档的 ID.解决此问题的推荐方法是什么?

The subject sub-document gets added in the performance sub-document array which is itself nested in the scores sub-document array. Notice that the newly inserted sub-document is assigned with its own ID, as instituted by the defined schema. Even if I get back the entire document, that's not very helpful. I specifically need the ID of that newly inserted sub-document. What is the recommended approach to this problem?

推荐答案

在这种情况下，我更喜欢将 ID 预先分配给子文档(即 sub._id = ObjectId() 或使用uuid 包(如果您喜欢 uuid):清晰且可预测.

In this case I prefer pre-assign the ID to the sub-document (i.e. sub._id = ObjectId() or use uuid package if you prefer uuid): is clear and predictable.

还请记住，如果您经常通过 subdoc id 进行查询，最好在集合中为此用例添加(使用 ensureIndex())索引.

Also remember that if you frequent query by a subdoc id is good to add (using ensureIndex()) an index for this use case in the collection.

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