Mongoose $inc updateMany cannot increment with non-numeric argument - node.js

Question

Node API, where we have Mongo collection of profiles, and every profile have subscription_plan which represent rest of the days they have paid for using app.
Now, i works on part of the backend which should decrease subscription_plan of all profiles by 1.
The problem is, subscription_plan is declared as String, so I can't just decrease it by 1
I tried with this after getting some tips here:
router.put('/reduceSubscription', async (req, res) => {
try {
const updatedProfiles = await Profile.updateMany({ is_active: true }, [
{
$set: {
subscription_plan: {
$toString: {
$subtract: [{ $toInt: '$subscription_plan' }, 1]
}
}
}
}
]).exec();
console.log(updatedProfiles);
} catch (err) {
res.status(500).send({ msg: err.message });
}
});
After testing in postman, i got message:
"msg": "Failed to parse number 'NaN' in $convert with no onError value: Bad digit \"N\" while parsing NaN"
I would appreciate any help or code snippet that will help me solve this problem.
Thanks :)

Answer 1

What you are trying to do (as the error states) is not possible with the current schema simply because your Profile model schema defines subscription_plan as a String and $inc only works on numeric fields.
Either change the schema type for that field or use the aggregate pipeline to update the value by creating a pipeline that has a set of aggregation pipeline operations i.e. 1) get the current value, 2) convert it to a numeric value using $toInt, 3) decrement the value with $subtract and 4) set the new value back to string using $toString:
router.put('/reduceSubscription', async (req, res) => {
try {
await Profile.updateMany(
{ is_active: true },
[
{ '$set': {
'subscription_plan': {
'$toString': {
'$subtract': [
{ '$toInt': '$subscription_plan' },
1
]
}
}
} }
]
).exec();
res.json('Profiles updated');
} catch (err) {
res.status(500).send({ msg: err.message });
}
});