Class-transformer: classToPlain fails to transform mongo ObjectId to string

[VivienAdnot]

Hello guys,
I created an endpoint with routing-controller, from @pleerock :

import { JsonController, Param, Get, NotFoundError } from "routing-controllers";

@JsonController("my-route")
export class MyController {
    @Get("/:marketingId")
    async getOne(@Param("marketingId") marketingId: string) {
        let marketing: MarketingAutomation = await MyDB().findOne({
            '_id': new ObjectId(marketingId)
        });
        console.log(marketing._id instanceOf ObjectId) // writes true

        if (!!marketing && marketing._id) {
            return classToPlain(marketing);
        }

        throw new NotFoundError(`User was not found.`);
    }
}

The model, MarketingAutomation is:

import { ObjectId } from "mongodb";
import { IsDefined, IsString } from 'class-validator';
import { Expose } from 'class-transformer';

export class MarketingAutomation {
    _id?: ObjectId;
    companyId?: ObjectId;

    @IsDefined()
    @IsString()
    name: string;

    @Expose({name: '_id', toPlainOnly: true})
    id() { return this._id.toHexString();}

    @Expose({name: 'companyId', toPlainOnly: true})
    _companyId() { return this.companyId.toHexString();}    
}

The response is :

{
    "_id": {
        "_bsontype": "ObjectID",
        "id": {"0":89,"1":186,"2":173,"3":122,"4":253,"5":210,"6":194,"7":101,"8":17,"9":9,"10":73,"11":26}
    },
    "name": "test",
    "companyId": {
        "_bsontype": "ObjectID",
        "id": {"0":87,"1":63,"2":67,"3":251,"4":214,"5":195,"6":157,"7":16,"8":0,"9":72,"10":9,"11":211}
    }
}

The response I would like to receive is:

{
    "_id": "59baad7afdd2c2651109491a",
    "name": "test",
    "companyId": "rf41237afdd2c2651109gt45"
}

When you look at the response, you see that _id and companyId are not transformed in strings
Do you know how to achieve it ?

Thank you very much !

[Petr0vi4]

Can't reproduce this behavior, but I think you have name conflict. Try to add @Exclude to ObjectId properties:

  @Exclude({toPlainOnly: true})
  _id?: ObjectID;
  @Exclude({toPlainOnly: true})
  companyId?: ObjectID;

[Petr0vi4]

Do you really need these id and _companyId getters?
You can add @Transform decorator to existing properties instead:

@Transform((id: ObjectID) => id.toHexString(), {toPlainOnly: true})
_id?: ObjectID;
@Transform((id: ObjectID) => id.toHexString(), {toPlainOnly: true})
companyId?: ObjectID;

[VivienAdnot]

Thank @Petr0vi4, I tried it but it fails:

    @Type(() => ObjectId)
    @Transform(value => value.toHexString(), {toPlainOnly: true})
    _id?: ObjectId;

```json
{
"name": "TypeError",
"message": "Cannot read property 'prototype' of undefined",
"stack": "TypeError: Cannot read property 'prototype' of undefined.../node_modules/class-transformer/metadata/MetadataStorage.js:131:84"
}

Do you know what happens ?
I found an alternative but it is not as clean:

```ts
let instance = plainToClass(classType, JSON.parse(JSON.stringify(plain)));
return classToPlain(instance);

[vimmerru]

I have the same issue. Looks like there is some implicit to string conversion. I found the following workaround:

    @Expose()
    public get id() {
        return this._id ? this._id.toHexString() : undefined;
    }

    @Exclude()
    // tslint:disable-next-line:variable-name
    public _id?: ObjectId;

[NoNameProvided]

@VivienAdnot The reason for this is that when the JS engine transforms the object it calls the toJSON function recursively under the hood and ObjectId doesn't provide a custom implementation for it, so the default built-in will run what outputs the underlying object.

The proper solution is what @Petr0vi4 wrote in his second comment.

I will go ahead and close this, feel free to continue the discussion if you still have any question.

[github-actions[bot]]

This issue has been automatically locked since there has not been any recent activity after it was closed. Please open a new issue for related bugs.