# update or add a property to subdocuments of all found documents (MongoDB)

> How to update or add a property to subdocuments in MongoDB.

Source: https://curiouslychase.com/engineering/update-or-add-a-property-to-subdocuments-of-all-found-documents-mongodb/

This `updateMany` finds all `agreement_versions` that has a `participants` property on it and sets each member (the `$[]` selects each individual member) of `participants` to have a field called `role` with a value of `"Decider"`.

```javascript
db.agreement_versions.updateMany(
  {
    participants: {
      $exists: true,
    },
  },
  {
    $set: {
      "participants.$[].role": "Decider",
    },
  }
);

```