Upsert timeseries in Mongodb v5 - v6 - mongodb

Question

I'm reading the documentation about Timeseries in Mongodb v5 - v6 and I don't understand if it's possible to upsert a record after it has been saved; for example if I have a record like this (the "name" field is the "metadata" ):
{
_id: ObjectId("6560a0ef02a1877734a9df66")
timestamp: 2022-11-24T01:00:00.000Z,
name: 'sensor1',
pressure: 5,
temperature: 25
}
is it possible to update the value of the "pressure" field after the record has been saved?
From the official mongo documentation, inside the "Time Series Collection Limitations" section, I read that: The update command may only modify the metaField field value.
Is there a way to upsert also other field? Thanks a lot.

Answer 1

No, updating the pressure field in your example is impossible with update alone, and upsert doesn't exist for time series collections.
The only functions currently available for time series collections are Delete and Update, but they only work on the metaField values, so in your example, we can only update/rename 'sensor1'.
The only workaround I know to update values is as follows:
Get a copy of all documents matched on the metaField values.
Update desired values on the copied documents.
Delete the original documents from the database
Insert your new copy of the documents into the database.
Here's a way to update values on a time series collections, using the MongoDB Shell (mongosh)
First, we create a test database. The important part here is the metaField named "metadata." This field will be an object/dictionary that stores multiple fields.
db.createCollection(
"test_coll",
{
timeseries: {
timeField: "timestamp",
metaField: "metadata",
granularity: "hours"
}
}
)
Then we add some test data to the collection. Note the 'metadata' is an object/dictionary that stores two fields named
sensorName and sensorLocation.
db.test_coll.insertMany( [
{
"metadata": { "sensorName": "sensor1", "sensorLocation": "outside"},
"timestamp": ISODate("2022-11-24T01:00:00.000Z"),
"pressure": 5,
"temperature": 32
},
{
"metadata": { "sensorName": "sensor1", "sensorLocation": "outside" },
"timestamp": ISODate("2022-11-24T02:00:00.000Z"),
"pressure": 6,
"temperature": 35
},
{
"metadata": { "sensorName": "sensor2", "sensorLocation": "inside" },
"timestamp": ISODate("2022-11-24T01:00:00.000Z"),
"pressure": 7,
"temperature": 72
},
] )
In your example we want to update the 'pressure' field which currently holds the pressure value of 5. So, we need to find all documents where the metaField 'metadata.sensorName' has a value of 'sensor1' and store all the found documents in a variable called old_docs.
var old_docs = db.test_coll.find({ "metadata.sensorName": "sensor1" })
Next, we loop through the documents (old_docs), updating them as needed. We add the documents (updated or not) to a variable named updated_docs. In this example, we are looping through all 'sensor1' documents, and if the timestamp is equal to '2022-11-24T01:00:00.000Z' we update the 'pressure' field with the value 555 ( which was initially 5 ). Alternatively, we could search for a specific _id here instead of a particular timestamp.
Note that there is a 'pressure' value of 7 at the
timestamp 2022-11-24T01:00:00.000Z, as well, but its value will remain the same because we are only looping through all 'sensor1' documents, so the document with sensorName set to sensor2 will not be updated.
var updated_docs = [];
while (old_docs.hasNext()) {
var doc = old_docs.next();
if (doc.timestamp.getTime() == ISODate("2022-11-24T01:00:00.000Z").getTime()){
print(doc.pressure)
doc.pressure = 555
}
updated_docs.push(doc)
}
We now have a copy of all the documents for 'sensor1' and we have updated our desired fields.
Next, we delete all documents with the metaField 'metadata.sensorName' equal to 'sensor1' ( on an actual database, please don't forget to backup first )
db.test_coll.deleteMany({ "metadata.sensorName": "sensor1" })
And finally, we insert our updated documents into the database.
db.test_coll.insertMany(updated_docs)
This workaround will update values, but it will not upsert them.