how to insert autoincrement number with my mongoose collection

Question

I am newbie to mongoose, I have a mongoose schema like this:

var user = mongoose.Schema({
    userID: {
        type: String,
        required:true
    },
           


        

Answer 1

Following the MongoDB tutorial, Create an Auto-Incrementing Sequence Field, you need to first create a separate counters collection to track the last number sequence used. The _id field contains the sequence name i.e. the userID field in the user collection and the seq field contains the last value of the sequence.

To start with, insert into the counters collection the initial value for the userID:

db.counter.insert(
   {
      "_id": "userID",
      "seq": 0
   }
)

Having populated the counters collection, generate its schema in Mongoose:

var counterSchema = mongoose.Schema({
    "_id": { "type": String, "required": true },
    "seq": { "type": Number, "default": 0 }
});

var counter = mongoose.model('counter', counterSchema);

Then redefine your user schema so that when you save a user model it first calls the counter model's findByIdAndUpdate() method to atomically increment the seq value and return this new value which can then be used as the next userID value:

var userSchema = mongoose.Schema({
    "userID": { "type": String, "required": true },
    "firstname": { "type": String },
    "lastname": { "type": String },
    // other properties ...
    }, { "collection": "user" }
);

userSchema.pre("save", function (next) {
    var doc = this;
    counter.findByIdAndUpdate(
        { "_id": "userID" }, 
        { "$inc": { "seq": 1 } }
    , function(error, counter)   {
        if(error) return next(error);
        doc.userID = counter.seq.toString();
        next();
    });
});