Shuffling composite _id key issue

[Nainterceptor]

Hello,

Issue : When I'm saving an object with a composite _id, update will be silently ignored.

Proof of the issue :

const co = require('co');
const mongoose = require('mongoose');

mongoose.Promise = global.Promise;
const { Schema } = mongoose;

co(function*() {
    yield mongoose.connect('mongodb://localhost/test');
    console.log('foo');
    const schema = new Schema({
        _id: {
            key1: String,
            key2: String,
        },
        content: String,
    });

    const Model = mongoose.model('test', schema);

    let object = new Model();
    object._id = {key1: "foo", key2: "bar"}; //Saved
    object = yield object.save();
    object.content = 'Hello';
    object = yield object.save(); //Return object with right content, but not saved
    console.log(object);
}).catch(e => console.log(e));

Investigating :
Sorting of keys in the ID is not insured, so {key1, key2} will find the doc, but {key2,key1} will match with 0 docs.
When Mongoose call update, (btw, update is deprecated now, please replace by updateOne) where may be with the bad order for keys.
On the FindOne, _id object may be shuffled. So, on update, bad sorted _id may be embed into the updateOne, so the save() will fail. (Return 0 documents modified, but no error throwed).

Workaround :
I'm using a workaround, but with a potential performance issue (not benchmarked), I've overrided the Model of mongoose, to decompose _id key. {_id: {key1, key2}} will become {"_id.key1", "_id.key2"} With this syntax, order is not important.

To override model, please see PR #4541, then you can do something like that (findById overrided too, for example) :

const co = require('co');
const mongoose = require('mongoose');
const MongooseModel = require('mongoose/lib/model');

mongoose.Promise = global.Promise;
const { Schema } = mongoose;

const oldWhere = MongooseModel.prototype.$__where;

function decompositionOfKeys(root, object) {
    const criteria = {};
    const compoundIdKeys = Object.keys(object);
    for (const compoundIdKey of compoundIdKeys) {
        criteria[[root, compoundIdKey].join('.')] = object[compoundIdKey];
    }
    return criteria;
}

MongooseModel.prototype.$__where = function __where(where) {
    where = oldWhere.call(this, where);
    if (where._id && !where._id.str) {
        const id = where._id;
        delete where._id;
        Object.assign(where, decompositionOfKeys('_id', id));
    }
    return where;
};

MongooseModel.prototype.findById = function findById(id, ...rest) {
    const criteria = {};
    if (id.str) {
        criteria._id = id;
    } else {
        Object.assign(criteria, decompositionOfKeys('_id', id));
    }
    return this.findOne(criteria, ...rest);
};

mongoose.Model = MongooseModel;

co(function*() {
    yield mongoose.connect('mongodb://localhost/test');
    const schema = new Schema({
        _id: {
            key1: String,
            key2: String,
        },
        content: String,
    });

    const Model = mongoose.model('test', schema);

    let object = new Model();
    object._id = {key1: "foo", key2: "bar"}; //Saved
    object = yield object.save();
    object.content = 'Hello';
    object = yield object.save(); //Return object with right content, and is saved
    console.log(object);
}).catch(e => console.log(e));

Have a nice day,
Gaël

[vkarpov15]

Good catch! Will fix this for next release

[vkarpov15]

So looking into this, this is actually a very difficult problem tied into #2749, my least favorite legacy mongoose feature. Fixing is gonna take another week or two, thanks for your patience 🍻 🌴