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

Question

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?

score 428 · Accepted Answer · edited Feb 20 '21 at 23:13

428

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);

edited Feb 20 '21 at 23:13

Kaspar Lee

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answered Jun 22 '13 at 18:44

throrin19

17,796
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2

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](http://stackoverflow.com/questions/38151433/mongoose-inserts-extra-id-in-array-of-objects-corresponding-to-related-entity) on SO today. – Web User Jul 01 '16 at 18:38
1

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? – Web User Jul 12 '16 at 22:45
1

Have you try, for the third level to set `{ _id : true }` ? – throrin19 Jul 13 '16 at 07:06
1

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. – Web User Jul 13 '16 at 14:53

score 210 · Answer 2 · edited Feb 20 '21 at 23:13

210

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

edited Feb 20 '21 at 23:13

Kaspar Lee

5,446
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answered Dec 13 '13 at 02:43

Joel Grenon

3,173
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19

score 57 · Answer 3 · answered May 28 '14 at 05:12

57

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
   }
}

answered May 28 '14 at 05:12

wlingke

4,699
4
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jemiloii · Answer 4 · 2019-03-19T15:16:48.297

32

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"
      }
    ]
}

edited Mar 19 '19 at 15:16

answered Oct 14 '16 at 23:08

jemiloii

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is there a way to make unique across entire collection? – Saitama Jan 17 '18 at 05:01
Probably not with this method, but you could always try. `_id` is a field rather than a constraint. – jemiloii Jan 17 '18 at 16:52
if during the creation of that sub-document, i explicitly assign ```_id = mongoose.Types.ObjectId()```, would that _id be unique across collection then? – Saitama Jan 17 '18 at 16:55
just open a new stack overflow, this way you can get many people to answer at once~ – jemiloii Jan 18 '18 at 16:29

Deeksha Sharma · Answer 5 · 2019-04-25T08:10:46.973

6

You can use either of the one

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

},{ _id : false });

or

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

});

Check your mongoose version before using the second option

edited Apr 25 '19 at 08:10

answered Apr 25 '19 at 06:21

Deeksha Sharma

3,199
1
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score 4 · Answer 6 · answered Apr 04 '20 at 09:07

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.

score 4 · Answer 7 · answered Apr 04 '22 at 03:37

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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