const userDBSchema = new Schema({
    userName: {
        type:String
    },
    musicType: {
        type: String,
    },
}, { collection: 'userData' });

exports.saveUser = (req, res) => {
    const username = req.params.user;

    const newUser = new UserInfoDb(req.body, {'collection': username});
    newUser.save((err, response) => {
      //save operation
    });
};

{
    "message": "document must have an _id before saving",
    "name": "MongooseError"
}

_id: {
        type: mongoose.Schema.Types.ObjectId,
        index: true,
        required: true,
        auto: true
    },

{
    "errors": {
        "_id": {
            "message": "Path `_id` is required.",
            "name": "ValidatorError",
            "properties": {
                "message": "Path `_id` is required.",
                "type": "required",
                "path": "_id"
            },
            "kind": "required",
            "path": "_id"
        }
    },
    "_message": "userDB validation failed",
    "message": "userDB validation failed: _id: Path `_id` is required.",
    "name": "ValidationError"
}