What is the "__v" field in Mongoose - node.js

Question

I'm using Mongoose version 3 with MongoDB version 2.2. I've noticed a __v field has started appearing in my MongoDB documents. Is it something to do with versioning? How is it used?

Answer 1

From here:
The versionKey is a property set on each document when first created
by Mongoose. This keys value contains the internal revision of the
document. The name of this document property is configurable. The
default is __v.
If this conflicts with your application you can configure as such:
new Schema({..}, { versionKey: '_somethingElse' })

Answer 2

Well, I can't see Tony's solution...so I have to handle it myself...
If you don't need version_key, you can just:
var UserSchema = new mongoose.Schema({
nickname: String,
reg_time: {type: Date, default: Date.now}
}, {
versionKey: false // You should be aware of the outcome after set to false
});
Setting the versionKey to false means the document is no longer versioned.
This is problematic if the document contains an array of subdocuments. One of the subdocuments could be deleted, reducing the size of the array. Later on, another operation could access the subdocument in the array at it's original position.
Since the array is now smaller, it may accidentally access the wrong subdocument in the array.
The versionKey solves this by associating the document with the a versionKey, used by mongoose internally to make sure it accesses the right collection version.
More information can be found at: http://aaronheckmann.blogspot.com/2012/06/mongoose-v3-part-1-versioning.html

Answer 3

For remove in NestJS need to add option to Schema() decorator
#Schema({ versionKey: false })

Answer 4

It is possible to disable the version key if you don't need it.
See this example:
var User = new mongoose.Schema({
FullName:{
type :String,
},
BirthDay:{
type :String,
},
Address:{
type :String,
},
Gender:{
type:String,
},
PhoneNumber:{
type:Number,
ref:'Account'
},
AccountID:{
type: Schema.Types.ObjectId,
ref: 'Account'
},
UserName:{
type:String,
ref:'Account'
}
},{collection:'User',
versionKey: false //here
});

Answer 5

It is the version key.It gets updated whenever a new update is made. I personally don't like to disable it .
Read this solution if you want to know more
[1]: Mongoose versioning: when is it safe to disable it?

Answer 6

the '__v' field in our 'document' serves 'optimisticConcurrency' concerns.
This term basically means in mongoose :
let, you grabed a document by 'findOne, findById' but not used save() method of mongoose yet. and what if at this interval, any other code grabed same document and used .save() method before the first document instance.
at this use case, if we want to (mongoose specific) throw a version error kinda thing, we use optimisticConcurrency: true option in schema.
and then mongoose will use '__v1' to compare these two document.
without optimisticConcurrency: true option. '__v' has no has no effect. and mongoose will not increase it by 1.
Note : in 'findOneAndUpdate' kinda operations, will not update '__v'. (only save() updates)

Answer 7

The __v field is called the version key. It describes the internal revision of a document. This __v field is used to track the revisions of a document. By default, its value is zero (__v:0).
If you don't want to use this version key you can use the versionKey: false as mongoose.Schema parameter.
You can follow this example...
const mongoose = require('mongoose');
const userSchema = mongoose.Schema(
{
name: {
type: String,
require: true
},
email: {
type: String,
unique: true
},
password: {
type: String,
}
},
{
timestamps: true,
versionKey: false, // Here You have to add.
}
)
module.exports = mongoose.model('tbl_user', userSchema)

Answer 8

We can use versionKey: false in Schema definition
'use strict';
const mongoose = require('mongoose');
export class Account extends mongoose.Schema {
constructor(manager) {
var trans = {
tran_date: Date,
particulars: String,
debit: Number,
credit: Number,
balance: Number
}
super({
account_number: Number,
account_name: String,
ifsc_code: String,
password: String,
currency: String,
balance: Number,
beneficiaries: Array,
transaction: [trans]
}, {
versionKey: false // set to false then it wont create in mongodb
});
this.pre('remove', function(next) {
manager
.getModel(BENEFICIARY_MODEL)
.remove({
_id: {
$in: this.beneficiaries
}
})
.exec();
next();
});
}
}