__v field causing mongo errors

I’m getting this error when saving a document:

{
    name: "MongoError",
    err: "Field name duplication not allowed with modifiers",
    code: 10150,
    n: 0,
    connectionId: 1,
    ok: 1
}

the mongo diaglog shows that the query in question did this:

update flags: 0 q: {
    __v: 11,
    _id: ObjectId('527a7c1ca2d740dd0f000004')
}
o: {
    $set: {
        __v: 11,
        aaaa.bbbbb: [{
            _id: ObjectId('52a115780594725664000001'),
            type: "xxxxx",
            name: "xxxxxxxxxxxxxxxx"
        }],
        cccc.ddddd: [{
            _id: ObjectId('527136c893312c254a0000b7'),
            type: "xxxxx",
            name: "xxxxxxx"
        }, {
            _id: ObjectId('52a115780594725664000001'),
            type: "xxxxx",
            name: "xxxxxxxxxxxxxxx"
        }],
        tttttt: new Date(1393008423258)
    },
    $inc: {
        __v: 1
    }
}

Not that it’s both {$set: {__v: 11}} and {$inc: {__v:1}}, which mongo does not like.

[dillonkrug]

While I was trying to write a test case I realized the source of the error. We send the document as JSON to the client, where it is modified, then the client sends it back and we merge any changed data with a clean copy from the database, then save it.

the $set : __v part of the invalid query comes from the merge, and the $inc : __v comes from mongoose internally, because an array field was modified.

This problem can easily be solved by our code simply ignoring the __v field during the merge.

That said, if setting the __v field causes difficult to trace errors (“Field name duplication not allowed with modifiers” is all the information available without going to the mongo diaglog) perhaps a preemptive warning of some sort would be appropriate.

The simplest way to reproduce this error:

var mongoose = require('mongoose');

mongoose.connect('mongodb://localhost:27017/test');

var Test = mongoose.model('Test', new mongoose.Schema({
    id: String,
    field: [{}],
}));

var doc = new Test();
doc.save(function(err) {
    Test.findOne(function(err, doc) {
        doc.__v = 123;
        doc.field.push({_id: 'xxxxx', type: 'nnn'});
        doc.save(function(err) {
            console.log(err);
        })
    })
})

[chenop]

Please check mongoose version compatibility with MongoDB version: http://mongoosejs.com/docs/compatibility.html

There is a possibility that the MongoDB version you are using require higher Mongoose version.

In my case I use MLab MongoDB version 3.3.6 with Mongoose version 4 - Upgrading to Mongoose 5 solve the issue.