I'm working with node.js and mongoose. I'm creating a REST API to expose my User model:

var userSchema = new Schema({
 _id: {type:Number},
 username: {type:String},
 age: {type:Number},
 genre:{type: Number,ref:'Genre'},
 country: {type: Number,ref:'Country'}
});

As you can see I decided to include an _id field, so if I want to create a new user I'll need to generate the value for this field, for example:

exports.createUser = function(req,res){
 var user = new User({
    _id: //Generate and assing value here
        //Other properties are retrieved from the request object
 });
};

How could I "generate" or assign a value to my _id field properly? How does mongo deals with this?

I'm working with node.js and mongoose. I'm creating a REST API to expose my User model:

var userSchema = new Schema({
 _id: {type:Number},
 username: {type:String},
 age: {type:Number},
 genre:{type: Number,ref:'Genre'},
 country: {type: Number,ref:'Country'}
});

As you can see I decided to include an _id field, so if I want to create a new user I'll need to generate the value for this field, for example:

exports.createUser = function(req,res){
 var user = new User({
    _id: //Generate and assing value here
        //Other properties are retrieved from the request object
 });
};

How could I "generate" or assign a value to my _id field properly? How does mongo deals with this?

• javascript
• node.js
• mongodb
• express
• mongoose

Share Improve this question Follow asked Jan 13, 2014 at 16:01 user1659653user1659653 33422 gold badges66 silver badges1515 bronze badges 1

• 2 I'd suggest you let MongoDB set the value for your _id field. If you need an additional identifier field you can go ahead define a different field (say key) and use whatever algorithm you feel like for it (a sequential field or a GUID) – Hector Correa Commented Jan 13, 2014 at 16:10

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2 Answers 2

Sorted by: Reset to default 3

I never used mongoose. but if _id is not included in insert query, mongodb driver will generate _ids for you as an ObjectId object. and if you wish to use your own _ids, it's up to you to decide about its type and length, and also you have to guarantee its uniqueness among the collection because any attempt to insert a document with a duplicated _id will fail.

accepted answer of this question may be useful, if you are looking for a method for creating custom _ids that provides a decent degree of guaranteed uniqueness.

mongoDB requires that _id, if supplied, be unique. If _id is not supplied, it is created by the client-side driver (i.e. NOT the mongod server!) as a 12-byte BSON ObjectId with the following structure:

4-byte value representing the seconds since the Unix epoch,
3-byte machine identifier,
2-byte process id, and
3-byte counter, starting with a random value.

more info available here: http://docs.mongodb/manual/reference/object-id