Mongoose __v when does it change

Question

According to http://aaronheckmann.tumblr.com/post/48943525537/mongoose-v3-part-1-versioning The version field __v is suppose to change when array elements are shifted out of their original position.

I run a test code (Mongoose version 3.8.15):

var mongoose = require('mongoose');

var db = mongoose.connection;
mongoose.connect('mongodb://localhost:27017/node_test');
db.on('error', console.error.bind(console, 'connection error:'));

var testSchema = mongoose.Schema({
  name: String,
  arr: [Number]
})
var Test = mongoose.model('Test', testSchema);

var t = Test();
t.name = 'hi'
t.arr = [1, 2, 3, 4, 5, 6];
t.save(function (err, result) {
  console.log(result)
  Test.update({'name': 'hi'}, {$pull: {'arr': 3}}, function(err2, result2) {
    console.log(result2)
    Test.find({'name': 'hi'}, function(err3, result3) {
      console.log(result3);
      db.close();
    });
  });
});

Output:

{ __v: 0,
  name: 'hi',
  _id: 53f594a0113832871c2eea89,
  arr: [ 1, 2, 3, 4, 5, 6 ] }
1
[ { _id: 53f594a0113832871c2eea89,
    name: 'hi',
    __v: 0,
    arr: [ 1, 2, 4, 5, 6 ] } ]

So, number 3 is removed which introduced a disruptive change to the array if any code is to attempt to access it by the position of its index. Why isn't the version incremented?

Christian P · Accepted Answer · 2014-08-21T08:07:27.037

5

The author of the article wasn't very clear when the version increment will be internally applied, because as you found out the version field is not updated when you're using the update command.

If you replace the update command with Mongoose pull method on your array the version field will be incremented:

var t = Test();
t.name = 'hi'
t.arr = [1, 2, 3, 4, 5, 6];

t.save(function (err, result) {
    console.log(result);

    // use Mongoose pull method on the array
    t.arr.pull(3);

    t.save(function(err2, result2) {
        console.log(result2)
    });
});

Results:

{ __v: 0,
  name: 'hi',
  _id: 53f59d2a6522edb12114b98c,
  arr: [ 1, 2, 3, 4, 5, 6 ] }
{ __v: 1,
  name: 'hi',
  _id: 53f59d2a6522edb12114b98c,
  arr: [ 1, 2, 4, 5, 6 ] }

Edit:

The update method on the model basically only builds and executes the query. The version checking / incrementing is done when you use the save method

edited Aug 21 '14 at 08:07

answered Aug 21 '14 at 07:19

Christian P

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Why is there the discrepancy? Is it because the update command goes directly to node-mongodb-native and Mongoose cannot intercept it? – huggie Aug 21 '14 at 07:37
@huggie , did you know about it ??.. mongoose can intercept change or not ??? – Nihal Chandwani May 06 '21 at 07:24
@NihalChandwani Sorry Nihai this is too long ago so I don't remember, also I'd imagine even if I have the knowledge it is is pretty outdated. – huggie May 07 '21 at 02:45

Mongoose __v when does it change

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