Mongoose nested ObjectId Array validation Dto

Question

I have a Dto which looks like this:

import { Type } from "class-transformer";
import { ArrayMinSize, IsArray, ValidateNested} from "class-validator";
import { ObjectId } from "mongoose";

export class MongoIdDto {
    @IsArray()
    @ValidateNested({each: true})
    @ArrayMinSize(1)
    @Type(() => ObjectId)
    ids: ObjectId[]
}

But this throws me an error: 'ObjectId' only refers to a type, but is being used as a value here.

How does this error occur?

Answer 1

This is a common import mistake:

ObjectId can be imported from mongoose and from mongoDB.

The mongoose import is a Type

The mongodb import is a class representation of the bson ObjectId Type

So to fix this issue change your import to: import { ObjectId } from "mongodb";

But actually there is an option to validate MongoIds with this:

export class MongoIdArrayDto {
    @IsMongoId({each: true})
    @ArrayMinSize(1)
    ids: ObjectId[]
}