Stop Mongoose from creating _id property for sub-document array items

node.js mongodb mongoose subdocument

If you have subdocument arrays, Mongoose automatically creates ids for each one. Example:

{
    _id: "mainId"
    subDocArray: [
      {
        _id: "unwantedId",
        field: "value"
      },
      {
        _id: "unwantedId",
        field: "value"
      }
    ]
}

Is there a way to tell Mongoose to not create ids for objects within an array?

Kaspar Lee

It's simple, you can define this in the subschema :

var mongoose = require("mongoose");

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

var schema = mongoose.Schema({
    // schema content
    subSchemaCollection : [subSchema]
});

var model = mongoose.model('tablename', schema);

will this skip _id fields even in the subSchema collection, or only in the case where the subSchema is being used to embed as array of sub-document items? I ask this particularly because of my own question on SO today.

I use two levels of nested sub-schema collections. In other words, I have a subSchema collection similar to your example. Within that, I use another different sub-schema collection. I want only the first level sub-schema model instances to not use ids, but the second level (nested) sub-schema model instances need to have ids. When I use your solution, that is, specifying { _id: false }, both levels of sub-schema are without ids. Any way to work around this behavior?

Have you try, for the third level to set { _id : true } ?

what I tried yesterday was change this:

let studentSchema = new Schema({ studentId: { type: ObjectId, ref: Student.modelName }, performance: [performanceSchema] }, { _id: false });

to this:

let studentSchema = new Schema({ _id: false, id: false, studentId: { type: ObjectId, ref: Student.modelName }, performance: [performanceSchema] });

and that stopped _id creation on the studentSchema but retained _id creation on the objects in the performance array of sub-documents. Not sure if both _id: false and id: false are needed.

Kaspar Lee

You can create sub-documents without schema and avoid _id. Just add _id: false to your subdocument declaration.

var schema = new mongoose.Schema({
   field1: {
      type: String
   },
   subdocArray: [{
      _id: false,
      field: { type: String }
   }]
});

This will prevent the creation of an _id field in your subdoc.

Tested in Mongoose v5.9.10

wlingke

Additionally, if you use an object literal syntax for specifying a sub-schema, you may also just add _id: false to supress it.

{
   sub: {
      property1: String,
      property2: String,
      _id: false
   }
}

jemiloii

I'm using mongoose 4.6.3 and all I had to do was add _id: false in the schema, no need to make a subschema.

{
    _id: ObjectId
    subDocArray: [
      {
        _id: false,
        field: "String"
      }
    ]
}

is there a way to make unique across entire collection?

Probably not with this method, but you could always try. _id is a field rather than a constraint.

if during the creation of that sub-document, i explicitly assign _id = mongoose.Types.ObjectId(), would that _id be unique across collection then?

just open a new stack overflow, this way you can get many people to answer at once~

Deeksha Sharma

You can use either of the one

var subSchema = mongoose.Schema({
//subschema fields    

},{ _id : false });

var subSchema = mongoose.Schema({
//subschema content
_id : false    

});

Check your mongoose version before using the second option

Oliver White

If you want to use a predefined schema (with _id) as subdocument (without _id), you can do as follow in theory :

const sourceSchema = mongoose.Schema({
    key : value
})
const subSourceSchema = sourceSchema.clone().set('_id',false);

But that didn't work for me. So I added that :

delete subSourceSchema.paths._id;

Now I can include subSourceSchema in my parent document without _id. I'm not sure this is the clean way to do it, but it work.

wongz

NestJS example for anyone looking for a solution with decorators

@Schema({_id: false})
export class MySubDocument {
    @Prop()
    id: string;
}

Below is some additional information from the Mongoose Schema Type definitions for id and _id:

/**
* Mongoose assigns each of your schemas an id virtual getter by default which returns the document's _id field
* cast to a string, or in the case of ObjectIds, its hexString.
*/
id?: boolean;

/**
* 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 schema at all, you may disable it using this option.
*/
_id?: boolean;

Stop Mongoose from creating _id property for sub-document array items

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