Documents in MongoDB automatically generate a unique key on the _id field. The value is an ObjectId, a byte data type that is very lightweight. (More details in the docs.)

When querying your DB, you'll be returned an ObjectID data type. There are several scenarios in a web application where that can become cumbersome:

• Converting your data to JSON
• Passing the ID as a query param
• Comparing between the string representation of the ID and the ObjectID data type

To navigate around it, you can project the value to a string any time you query the db.

Here's an initial example of querying a collection in an API method:

export async function getPeople(query = {}): Promise<Person[]> {
  const client = await clientPromise;
  const collection = client.db('your-db').collection('people');
  const people = await collection
    .find<People>(query)
    .toArray();

  return people;
}

To convert the _id value, we'll create an aggregation step to make the conversion with the $toString operator

  const addFieldAggregation = {
    $addFields: {
      _id: { $toString: '$_id' },
    }
  };

Now, when querying from your application, you can convert the string value back to an ObjectId to query the intended document. I'll just convert our query to an aggregation to accomplish this:

import { ObjectId } from 'mongodb';

export async function getPeople(query = {}): Promise<Person[]> {
  const client = await clientPromise;
  const collection = client.db('your-db').collection('people');
  const person = (await collection
    .aggregate([
      {
        $match: query,
      },
      addFieldAggregation
    ])
    .toArray()) as Person[];

  return person;
}

Voilà!