How to insert a field in an existing document in MongoSH

Question

I've to insert a new field with a boolean value in some documents in the students collection with the following structure:

{
  _id: ObjectId("61c9cffcf9b7043141272c5b"),
  createdAt: 2021-12-27T14:38:52.025Z,
  updatedAt: 2022-07-26T10:12:56.887Z,
  deletedAt: null,
  fullName: 'Karina Kuznetsova',
  address: 'Chicago IL',
  Major:'Computer Science',
  __v: 0,
}

I'm running the following query in MongoSH locally in Mongo Compass:

db.students.aggregate([
    {
        $match: { 
            "_id": ObjectId('61c9cffcf9b7043141272c5b')
        }
    },
    {
        $set: { "transferred": true }
    }   
]);

I'm expecting the field to be added to the document like this:

{
  _id: ObjectId("61c9cffcf9b7043141272c5b"),
  createdAt: 2021-12-27T14:38:52.025Z,
  updatedAt: 2022-07-26T10:12:56.887Z,
  deletedAt: null,
  fullName: 'Karina Kuznetsova',
  address: 'Chicago IL',
  Major:'Computer Science',
  __v: 0,
  transferred: true
}

However, the original document remains the same, without the transferred field.

Option 2

I've also tried this way:

const studentsList = db.students.find({
    "_id": ObjectId('61c9cffcf9b7043141272c5b')
});

studentsList.forEach(student => {
    const result = db.students.updateOne(
        { _id: student._id },
        {
            $set: { "transferred": true }
        });
});

What am I doing wrong?

Answer 1

Use the update function instead to update the document.

The aggregate function is used to return the queried document, but will not update the existing document in the collection.

db.students.update(
    {
        _id: ObjectId('61c9cffcf9b7043141272c5b')
    },
    {
        $set: { "transferred":true }
    });