Updating Nested Array Mongoose

Question

I am working on an express js application where I need to update a nested array. 1) Schema :

//Creating a mongoose schema
var userSchema = mongoose.Schema({
_id: {type: String, required:true},
name: String,
sensors: [{
    sensor_name: {type: String, required:true},
    measurements: [{time: String}]
}] });

2) Here is the code snippet and explanation is below:

router.route('/sensors_update/:_id/:sensor_name/')
.post(function (req, res) {
User.findOneAndUpdate({_id:req.body._id}, {$push: {"sensors" : 
{"sensor_name" : req.body.sensor_name , "measurements.0.time": req.body.time } } },
{new:true},function(err, newSensor) {
if (err)
res.send(err);
res.send(newSensor)
}); });

I am able to successfully update a value to the measurements array using the findOneAndUpdate with push technique but I'm failing when I try to add multiple measurements to the sensors array.

Here is current json I get if I get when I post a second measurement to the sensors array :

{
"_id": "Manasa",
"name": "Manasa Sub",
"__v": 0,
"sensors": [
{
  "sensor_name": "ras",
  "_id": "57da0a4bf3884d1fb2234c74",
  "measurements": [
    {
      "time": "8:00"
    }
  ]
},
{
  "sensor_name": "ras",
  "_id": "57da0a68f3884d1fb2234c75",
  "measurements": [
    {
      "time": "9:00"
    }
  ]
  }]} 

But the right format I want is posting multiple measurements with the sensors array like this :

Right JSON format would be :

 {
"_id" : "Manasa",
"name" : "Manasa Sub",
"sensors" : [ 
    {
        "sensor_name" : "ras",
        "_id" : ObjectId("57da0a4bf3884d1fb2234c74"),
        "measurements" : [ 
            {
                "time" : "8:00"
            }
        ],
        "measurements" : [ 
            {
                "time" : "9:00"
            }
        ]
    }],
"__v" : 0 }

Please suggest some ideas regarding this. Thanks in advance.

Answer 1

You might want to rethink your data model. As it is currently, you cannot accomplish what you want. The sensors field refers to an array. In the ideal document format that you have provided, you have a single object inside that array. Then inside that object, you have two fields with the exact same key. In a JSON object, or mongo document in this context, you can't have duplicate keys within the same object.

It's not clear exactly what you're looking for here, but perhaps it would be best to go for something like this:

{
"_id" : "Manasa",
"name" : "Manasa Sub",
"sensors" : [ 
    {
    "sensor_name" : "ras",
    "_id" : ObjectId("57da0a4bf3884d1fb2234c74"),
    "measurements" : [ 
        {
            "time" : "8:00"
        },
        {
            "time" : "9:00"
        }
    ]
},
{
    // next sensor in the sensors array with similar format
    "_id": "",
    "name": "",
    "measurements": []
}],
}

If this is what you want, then you can try this:

User.findOneAndUpdate(
    {  _id:req.body._id "sensors.sensor_name": req.body.sensor_name },
    { $push: { "sensors.0.measurements": { "time": req.body.time } } }
);

And as a side note, if you're only ever going to store a single string in each object in the measurements array, you might want to just store the actual values instead of the whole object { time: "value" }. You might find the data easier to handle this way.