Inserting a new object into an Array of objects

Question

Within a MongoDB collection I have a document that contains an object with various KV pairs to describe a particular sensor. The format of the configuration object is shown below. What I want to be able to do is add new array elements into the configuration e.g. rssi, which will themselves contain an array of objects. I will also want to remove objects within the array's. It feels like the $push and $pull operators should used. The query is being coded in golang. sensor_sn can be taken as a unique identifier. Any suggestions on how to accomplish this?

{
  "configuration": {
    "ta": [
      {
        "ident": 0,
        "description": "Temperature",
        "sensor_sn": "828082837284",
        "unit": "℃",
        "type": "number",
        "elemID": "ta0"
      },
      {
        "ident": 1,
        "description": "Temperature",
        "sensor_sn": "0258c40d0000",
        "unit": "℃",
        "type": "number",
        "elemID": "ta1"
      },
      {
        "ident": 2,
        "description": "Temperature",
        "sensor_sn": "ed9dc30d0000",
        "unit": "℃",
        "type": "number",
        "elemID": "ta2"
      }
    ],
    "rh": [
      {
        "ident": 0,
        "description": "Relative Humidity",
        "sensor_sn": "",
        "unit": "%",
        "type": "number",
        "elemID": "rh"
      }
    ],
    "vlt2": [
      {
        "ident": 0,
        "description": "Battery Voltage",
        "sensor_sn": "",
        "unit": "V",
        "type": "number",
        "elemID": "vlt2"
      }
    ],
    "pt": [
      {
        "ident": 0,
        "description": "Precipitation",
        "sensor_sn": "",
        "unit": "mm/tip",
        "type": "number",
        "elemID": "pt"
      }
    ]
  }
}

I've had a look thru various forums to see if I can find a suitable pattern to modify, but so far without understanding quite how to accomplish my objective. https://www.mongodb.com/docs/manual/reference/operator/update/pull/ MongoDB - Update or Insert object in array

dgm · Accepted Answer · 2022-12-02 14:00:44Z

0

Have you looked at $addToSet? It will add a value to an array if it doesn't already exist. $pull will remove a matching item from an array.

For both calls the setup is mostly the same. The way I do it is create a bson.M{} of the new or deleted array element, then create a bson.M{} update using the field name and the update defined above, lastly create the update using the $addToSet or $pull command and what you are setting.

Assuming you are using the MongoDB Go driver, you could try:

    theData := bson.M{"ident": 1, "description": "New item", "sensor_sn": "new sensor", "unit": "V", "type": "number", "elemID": "vlt2"}
    whatToChange := bson.M{"configuration.rssi": theData}

To add the element:
    update := bson.M{"$addToSet": whatToChange}
To delete it:
    update := bson.M{"$pull": whatToChange}

    _, err = theCollection.UpdateOne(
        context.Background(),
        bson.M{"_id": "itemID"},
        update,
    )

edited Dec 2, 2022 at 14:00

answered Dec 2, 2022 at 13:52

dgm

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1 Comment

Bruce Over a year ago

Thanks for the very quick answer. I did manage to get something similar working with $push, but I shall try the $addToSet operator and see if that is more efficient (for coding)

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