Failed to save document without define an _id in his model

[Royalsspirit]

Do you want to request a feature or report a bug?
Report a bug introduice since 5.4.11

What is the current behavior?
Since 5.4.11, an error occure when i want to save this document:

const mongoose = require('mongoose');

const myModel = new mongoose.Schema({
  query: {
    type: String,
    required: true,
  },
  user: {
    _id: false,
    name: {
      type: String,
      required: true,
    },
    firstname: {
      type: String,
      required: true,
    },
  },
  params: [
    {
      _id: false,
      name: {
        type: String,
        required: true,
      },
    },
  ],
  dateCreated: {
    type: Date,
    trim: true,
    default: Date.now,
  },
});

const model = mongoose.model('myModel', myModel);
const query = "I want this";
const params = [{"name":"with this"}];
const user= {"name":"toto", "firstname":"toto"};
const obj = {
    query,
    params,
    user
}
const response = new model(obj)
response.save(error => (error ? next(error) : res.send({ success: true })));

It's like mongoose don't generate an _id by default like in previous version.

I tried many things to fix the issue and i found that when i remove _id:false from user. I get what i expected or an other way is to define a _id in main document like

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

If the current behavior is a bug, please provide the steps to reproduce.

• install the last version of mongoose
• code above will failed but if you go back to 5.4.10. it works

What is the expected behavior?
Expect document has been created but have document must have an _id before saving mongooseError without any unique ID in my model but it worked before 5.4.10

Please mention your node.js, mongoose and MongoDB version.
node: v9.0.0
mongodb: v4.0.0
mongoose: v5.4.14

[mhombach]

I might misunderstand your issue but be aware of this:
In MongoDB (as in most likely every Database) EVERY document/entry must have a unuqie identifier, so that the Database can explicitly target that entry.

If a document does not have a value for the indexed field in a unique index, the index will store a null value for this document. Because of the unique constraint, MongoDB will only permit one document that lacks the indexed field. If there is more than one document without a value for the indexed field or is missing the indexed field, the index build will fail with a duplicate key error.
( Source: https://docs.mongodb.com/manual/core/index-unique )

So you MUST create some unique field because otherwise there could exist 2 or more document with the exact same attributes/values. And if that's the case, you and mongoDB are unable to target one entry without the other.

I hope this helps to clear things up for you.
If there is still another issue and i maybe didn't get what you asked for, please try to redefine your question :)

[Royalsspirit]

Hello mhombach, thank you for your reply.
I think, you understand my issue, i know that each documents must have an unique ID but in previous version 5.4.11, i didn't have to explicitly define it. It was like _id was defined by default.

I'im just wondering, if lastest version changed something about that.

[mhombach]

The _id is generated with an objectId by default, even when not defining that field.
You can change the field by defining it like for example _id: String. If you do that, you yourself have to take care of creating unique strings beeing used for that field.

There is an exception:
On SUB-Documents you can disable the default generation of id-fields by writing:

var subSchema = mongoose.Schema({
    //your subschema content
},{ _id : false });

On first glance this might seem irritating, but you have to keep in mind the difference between mongoose and MongoDB.
SUB-Documents are not "real" documents in mongodb. The "most parent" document is the "real" document (which is the "model" in mongoose).
SUB-documents are, inside the mongo-database, only objects with sub-attributes. A MongoDB-Query will retur na document and NOT a sub-document. So if you have an array of subdocuments in your parent one and you cannot explicitly target a specific subdocument because there is no _id, then for mongoDb this is no problem, because the document (parent one) is still targetable by the _id.

I don't think that this has changed in mongoose like.... ever....
So i think that you most likely did some other changes you were not aware of (switching document and SUB-document for example when re-designing your data-structure) :)

EDIT:
I might have found your problem:
You are defining the _id: false, on the wrong place.
Like in my given JS-example, you need to tell mongoose about this setting in a SECOND object in your schema. I am using a different style of defining my schemas, so you might want to look up how this is written in your example.

[Royalsspirit]

After reading your reply, i think i understood my problem.

SUB-Documents are not "real" documents in mongodb. The "most parent" document is the "real" document (which is the "model" in mongoose).

Yes, that's it ! I tought that my field params was considering as a subdocument but it's not (it's just a field :p). That's why i put _id: false in all fields define as object or array.

Otherwise, if i define params content as model and i put it in main model as subdocument. I have to set _id: false in second object parameter to not have _id as you said and as we can see here

In this situation, when _id: false is in wrong place, latest mongoose version is maybe more restrective than previous version.

Again, thank you for your time and your help mhombach

[mhombach]

Glad we figured your probleme out :)
I still think that some lines in your code changed between the mongoose-versions, because the handling of _id is very fundamental and should be coded into mongoose from the beginning... But well, your problem is solved, that' what counts =)
If you don't have any questions left, could you please close this issue? So other users, that want to help, can focus on other open issues ^^

[Royalsspirit]

I still think that some lines in your code changed between the mongoose-versions, because the handling of _id is very fundamental and should be coded into mongoose from the beginning...

I'm just saying, the latest version is maybe more restrective regarding model syntax since we conclude that i put _id:false in wrong place for params field

I have not changed anything between mongoose version. With the model i showed you, this issue is gone when i come back to 5.4.10 and occure with the latest.

Anyway, we found a solution to fix document must have an _id before saving in this case. I'm going to close this issue.

[mhombach]

Hmm... ok, if you checked that the same code produces different behaviour with just the versions changing, then you maybe should create a new issue with that in focus. With a small script to reproduce the difference, maybe maintainers can check if this is wanted behaviour or not :)

[vkarpov15]

@mhombach You're right about _id in the wrong place. However, this issue has nothing to do with the user failing to create an _id, they should not have to in this case because they aren't disabling _id on the top level schema

@Royalsspirit there will be a fix for this issue in 5.4.16, this issue was also reported in #7524. Please see my comments here: #7524 (comment)

[Royalsspirit]

@vkarpov15 Thank you very much for your reply.
So it was a reel issue even if i found it in incorrect schema declaration. Now i know how to disabled _id properly :)