After a backend error that is now fixed, I have a corrupted database where the category_ids field is a list of objects with the key “$oid” instead of actual ObjectId objects.

I’m attempting to fix it with this query:

db.products.updateMany(
  {
    "category_ids": {
      $exists: true,
      $type: "array",
      $elemMatch: {
        "$oid": { $exists: true, $type: "string" }
      }
    }
  },
  [
    {
      $set: {
        "category_ids": {
          $map: {
            input: "$category_ids",
            as: "item",
            in: {
              $mergeObjects: [
                "$$item",
                {
                  "$oid": {
                    $cond: [
                      {
                        $and: [
                          { $ne: ["$$item.$oid", null] },
                          { $type: "$$item.$oid", $eq: "string" }
                        ]
                      },
                      { $toObjectId: "$$item.$oid" },
                      "$$item.$oid"
                    ]
                  }
                }
              ]
            }
          }
        }
      }
    }
  ]
);

But I get a “MongoServerError: unknown operator: $oid” error.

A sample document looks like this:

{
  "_id": {
    "$oid": "674e47d1aa9a78ec88c7bf07"
  },
  "name": "Apple iPhone 16 Pro 256GB Dorado",
  "listed": true,
  "price": 1902,
  "currency": "USD",
  "pictures": [
    "https://www.example.com/asset1",
    "https://www.example.com/asset2",
    "https://www.example.com/asset3"
  ],
  "group_ids": [],
  "category_ids": [
    {
      "$oid": "674df1c7aa9a78ec88c7be9b"
    },
    {
      "$oid": "674dff94aa9a78ec88c7be9f"
    }
  ],
  "custom_fields": {
    "description": "blah blah blah"
  }
  "variants": [],
  "variant_selection_mode": "image",
  "variant_selection_fields": []
}

Here’s a screenshot comparing how a corrupted document looks like next to a non-corrupted one in MongoDB Compass:

screenshot
(top document is the corrupted one)

Any help would be greatly appreciated.

Thank you, peace