how to make primary key / _id optional to input in mongoose - angularjs

Question

I want make primary key no need to input but primary key auto generate in mongodb.
so, i use {type : ObjectId,required:false}, but it wont work because I let the primary key empty. so is there another ways to make pprimary key optional to input? Thankyou
rest api model
var mongoose = require("mongoose");
var Schema = mongoose.Schema;
var ObjectId = Schema.ObjectId
var accessmenu = new Schema({
_id : {type : ObjectId,required: false},
acc_id : String,
name : String,
read : Boolean,
execute : Boolean
},{ collection: 'access_menu'});
var accessmenu = mongoose.model("accessmenu",accessmenu);
module.exports.accessmenu = accessmenu;
rest api
app.put("/access_menu/:id",function(req,res){
var AccessMenu = new accessmenu({
_id : req.body._id,
acc_id : req.body.acc_id,
name : req.body.name,
read : req.body.read,
execute : req.body.execute
});
AccessMenu.save(function(err){
if(err)
{
accessmenu.update({_id : req.params.id},{$set:{acc_id : req.body.acc_id,
name : req.body.name,
read : req.body.read,
execute : req.body.execute
}},function(err,users){
if(err)
{
data['error'] = 1;
data['Access_Menu'] = "update faill";
res.json(data);
}
else
{
data['error'] = 0;
data['Access_Menu'] = "update success";
res.json(data);
}
});
}
else
{
data['error'] = 0;
data['Access_Menu'] = "input success";
res.json(data);
}
});
});
script.js
if($scope.data_acc_lv.length > 0)
{
for(var i = 0;i<$scope.data_acc_lv.length;i++)
{
var input3 = {
"_id" : $scope.data_acc_lv[i]._id,
"acc_id":$scope.accLvID,
"name": $scope.data_acc_lv[i].name,
"read": $scope.data_acc_lv[i].read,
"execute": $scope.data_acc_lv[i].execute
}
$http.put("http://localhost:22345/access_menu/" + $scope.data_acc_lv[i]._id,input3)
.success(function(res,err){
if(res.error == 0)
{
$scope.data_acc_lv.length = 0;
}
else
{
console.log(err);
}
});
}
}

Answer 1

Mongoose assigns each of your schemas an _id field by default if one is not passed into the Schema constructor. The type assigned is an ObjectId to coincide with MongoDB's default behavior.
If you don't want an _id added to your child schema at all, you may disable it using this option.
// disabled _id
var childSchema = new Schema({ name: String }, { _id: false });
var parentSchema = new Schema({ children: [childSchema] });
You can only use this option on sub-documents. Mongoose can't save a document without knowing its id, so you will get an error if you try to save a document without an _id.
http://mongoosejs.com/docs/guide.html