feat(document): add $inc() helper that increments numeric paths

[vkarpov15]

Fix #11915

Summary

See #11915. Right now, there's no way to use $inc with save(). doc.num += 2 becomes a $set.

With this change, you can explicitly increment a given path, and when you save(), Mongoose will send a $inc.

Examples

const schema = new Schema({
  counter: Number
});
Test = db.model('Test', schema);

await Test.create({ counter: 0 });
const doc = await Test.findOne();
assert.strictEqual(doc.counter, 0);
const doc2 = await Test.findOne();

doc2.counter = 1;
await doc2.save();

doc.$inc('counter');
await doc.save();

const res = await Test.findById(doc);
assert.equal(res.counter, 2);

[AbdelrahmanHafez]

One minor nitpick, otherwise LGTM. 👍

Kind of surprised by the number of scenarios we have to take into account for this to work properly.

[AbdelrahmanHafez]

On second thought, what do you think about the following syntax? How easy would it be to support it?

document.counter.$inc(1);
document.friends[3].age.$inc(1);

[vkarpov15]

@AbdelrahmanHafez document.counter.$inc(1); is unfortunately not viable. You can't define properties on primitives, it throws an error in strict mode.

[vkarpov15]

Re: number of cases, it is mostly just because I'm trying to be more defensive about shipping new features. In the past, we've often had edge cases in new features like "oh this doesn't work with subdocuments". So this time I'm trying to cover every potential bug I can think of with tests.

[Uzlopak]

LGTM

[Uzlopak]

LGTM