Pushing onto Mongo SubDoc of SubDoc array - arrays

Question

I'm going around in circles with this one so hoping someone can help. I'm building a nodejs application that receives sensor values from nodes. There can be multiple sensors on a node.
Using NodeJS, Mongod DB and Mongoose, all running on a raspberry pi, 3 I've built the following Schemas & Model:
var mongoose = require('mongoose');
var Schema = mongoose.Schema;
var valueSchema = new Schema ({
timestamp: {type: Date},
value: {}
});
var sensorSchema = new Schema ({
id: {type: Number},
type: {type: String},
description: {type: String},
ack: {type: Boolean},
values: [valueSchema]
});
var SensorNode = mongoose.model('SensorNode', {
id: {type: Number, required: true},
protocol: {},
sensors: [sensorSchema]
});
I can add in the node, and push sensors onto the sensors array, but I seem unable to push values onto the values array.
I've looked over a few other examples and questions on similar issues, and looked at using populate, but cant seem to get them to work.
Here is my code:
function saveValue(rsender, rsensor, payload) {
var value = {
values: {
timestamp: new Date().getTime(),
value: payload
}
}
SensorNode.findOneAndUpdate({
"id": rsender,
"sensors.id": rsensor
}, {
"$push": {
"sensors.$": value
}
}, function(err, result) {
if (err) {
console.log(err);
}
console.log(result);
});
}
This is returning undefined for the result and this error:
MongoError: exception: Cannot apply $push/$pushAll modifier to non-array
Values is definitely an array in the sensor schema.
I'm using readable ids rather than the auto assigned Mongo DB IDs for the sake of the UI, but I could use the MongoDB _id if that makes any difference, I don't see why it would?
Where am I going wrong ?

Answer 1

You're using positional operator $ so let's check the docs
The positional $ operator identifies an element in an array to update without explicitly specifying the position of the element in the array. To project, or return, an array element from a read operation, see the $ projection operator.
So sensors.$ will return one particular document from your sensors array. That's why you're getting an error. On this level of your document you can only replace this item by using $set. I bet you wanted to do something like this:
SensorNode.findOneAndUpdate({
"id": rsender,
"sensors.id": rsensor
}, {
"$push": {
"sensors.$.values": payload
}
});
This operation will just append payload to values array in one particular sensor with id equal to rsensor.