MongoDB: Set field value to 10 if less than 10, otherwise increment by one

Question

Consider the following code:

findAndModify({id: id}, undefined, {$inc: {counter: 1}, {$max: {counter: 10})

This fails with an error because both $inc and $max try to update the same field.

But what if I want to set the counter to 10 if its value is less than 10 and if not, increment its value by 1? How do I do that in one atomic operation?

Is there a way to apply the updates sequentially in a single operation?

Answer 1

I don't think that can be done in a single operation. However, you can create an aggregate query with the conditional statements that you then use in your update.

(async () => {
    try {
        const results = await Model.aggregate([
            { '$match': { 'id': id } },
            { '$project': { 
                'counter': { 
                    '$cond': [
                        { '$lt': ['$counter', 10 ] },
                        10,
                        { '$add': ['$counter', 1 ] }
                    ] 
                }
            } }
        ]).exec();

        const data = results[0];
        const { counter } = data;

        const doc = await Model.findOneAndUpdate({ id },
            { '$set': { counter } },
            { new: true }
        ).exec();

        console.log(doc);
    } 
    catch (err) {
        console.error(err);
    }
})()

---

For an atomic update, include a query that restricts the increment for documents that only have counter less than the given ceiling value of 10:

findAndModify(
    {
        'id': id,
        'counter': { '$lt': 10 } 
    }, undefined, 
    { '$inc': { 'counter': 1 } },
    callback
)