mongodb - transform an array of objects (key: 'keyname', value:'value') into fields named 'keyname' with corrresponding value

Question

The current structure of my mongodb documents is:

{
  "_id": "5c9376110a32bd172c0c5a28",
  "timestamp": 1553168075444,
  "content": [
    {
      "name": "temperature_x",
      "value": 2
    },
    {
      "name": "temperature_y",
      "value": 2
    },
    {
      "name": "temperature_z",
      "value": 0
    }
  ]
},
{
  "_id": "5c9376110a32bd172c0c5a28",
  "timestamp": 1553168075444,
  "content": [
    {
      "name": "temperature_x",
      "value": 2
    },
    {
      "name": "vibration_x",
      "value": 21
    },
    {
      "name": "vibration_z",
      "value": 10
    }
  ]
}

I'd like to obtain a queryable shortcut (a view?), that I'll query with python to make data-analysis/data-science, where the desired document structure is:

{
  "_id": "5c9376110a32bd172c0c5a28",
  "timestamp": 1553168075444,
  "temperature_x": 1,
  "temperature_y": 2,
  "temperature_z": 0
},
{
  "_id": "5c9376110a32bd172c0c5a28",
  "timestamp": 1553168075444,
  "temperature_x": 2,
  "vibration_y": 21,
  "vibration_z": 10
}

Any help is welcome

Thank you

A

Answer 1

You can use below aggregation

db.collection.aggregate([
  { "$replaceRoot": {
    "newRoot": {
      "$mergeObjects": [
        "$$ROOT",
        { "$arrayToObject": {
          "$map": {
            "input": "$content",
            "in": {
              "k": "$$this.name",
              "v": "$$this.value"
            }
          }
        }}
      ]
    }
  }},
  { "$project": { "content": 0 }}
])

Output

[
  {
    "_id": ObjectId("5a934e000102030405000000"),
    "temperature_x": 2,
    "temperature_y": 2,
    "temperature_z": 0,
    "timestamp": 1.553168075444e+12
  },
  {
    "_id": ObjectId("5a934e000102030405000001"),
    "temperature_x": 2,
    "timestamp": 1.553168075444e+12,
    "vibration_x": 21,
    "vibration_z": 10
  }
]