Auto Increment With Atlas Triggers

MongoDB Atlas
1

Hello. I am trying to implementing a playerID field - separate from _id - that auto increments from 1 onward with each new entry into my users collection. I have read and am trying to follow this tutorial but I’m not having any luck. I simply don’t understand the example code and I’m fairly new with MongoDB as well.

I have two collections: “users” and “playerIDCounter”. I would like to adapt the example code from the tutorial for these two collections and to increment on the playerID field rather than the _id field. So far I have not been able to get this to work.

The example code is:

exports = async function(changeEvent) {
    var docId = changeEvent.fullDocument._id;
    
    const countercollection = context.services.get("<ATLAS-CLUSTER>").db(changeEvent.ns.db).collection("counters");
    const studentcollection = context.services.get("<ATLAS-CLUSTER>").db(changeEvent.ns.db).collection(changeEvent.ns.coll);
    
    var counter = await countercollection.findOneAndUpdate({_id: changeEvent.ns },{ $inc: { seq_value: 1 }}, { returnNewDocument: true, upsert : true});
    var updateRes = await studentcollection.updateOne({_id : docId},{ $set : {studentId : counter.seq_value}});
    
    console.log(`Updated ${JSON.stringify(changeEvent.ns)} with counter ${counter.seq_value} result : ${JSON.stringify(updateRes)}`);
    };

I would appreciate anyone that can explain what’s actually going on here.

4

Hello @Aaron_Dubois ,

You need to replace with your cluster service name in 3rd and 4th line of the code.

The code in the example is an async function, in which first this is accessing the _id of the latest changed document. Then it is updating the next available document with the help of counter.

Can you share the error you are getting while trying to replicate this?

Thanks,
Tarun