mongodb 更新集合中的字段同时自动生成另一个字段

Question

I have a collection which contain data's like this:

[{
_id: a,
createdAt: "2020-11-10",
createdBy: "test@test.com",
features: {
first: true,
second: true
}},{
_id: b,
createdAt: "2020-11-10",
createdBy: "test@test.com",
features: {
first: false,
second: true
}}]

I would like to insert a new feature: third: true

db.collection.update(  { _id:...} , { $set: { features.third : true  } } 

My questions is, is that possible to insert a new line for one of this feature and at the same time when the mongodb is see that there is a field like "third" and the value is true, than mongodb is generated a new field (featureConfig) automaticly which value is an empty string? so the expected value is :

{
_id: b,
createdAt: "2020-11-10",
createdBy: "test@test.com",
features: {
first: false,
second: true,
third: true
},
featureConfig: "",
}

Any help would be appreciated.

Answer 1

Try this query and check if it work as expected ( example )

This is the query:

db.collection.aggregate([
  {
    "$match": {
      "id": 1
    }
  },
  {
    "$set": {
      "features.third": true
    }
  },
  {
    "$project": {
      "features": 1,
      "featureConfig": {
        "$cond": {
          "if": "$features.third",
          "then": "",
          "else": "$false"
        }
      }
    }
  }
])

The two initial stages are the same that you have, filter to match by id and set the value. Then I've used $project to create a field featureConfig based in a condition. If the features.third value is true, then create the field, otherwise not.