Why it needs to convert `{"$numberInt": "1"}` to `1` before restoring data with `mongorestore`? - mongodb

Question

I have some dumped BSON and JSON files from a MongoDB server running on Google Cloud Platform(GCP) and I want to restore the data into a new local server with version 4.0.3. However, I got errors showing that the indices cannot be restored. I had to convert {"$numberInt": "1"} in the JSON files to 1 to make the restoring process success. Why I need to take effort to fix the format of the dumped files. Is it due to the different versions between the source server and the target server or due to some things I did not do correctly?
I have googled and searched stack overflow, but I did not see any one discussed this problem. And the release note of MongoDB does not mention any changes related to this problem.
Here is the JSON example cannot accept by mongorestore with version 4.0.3
{
"options": {},
"indexes": [
{
"v": {
"$numberInt": "2"
},
"key": {
"_id": {
"$numberInt": "1"
}
},
"name": "_id_",
"ns": "demo.item"
},
{
"v": {
"$numberInt": "2"
},
"key": {
"itemId": {
"$numberDouble": "1.0"
}
},
"name": "itemId_1",
"ns": "demo.item"
}
],
"uuid": "8ce4755612da4d048b0fd38a793f2b55"
}
And this is the accepted one which is converted on my own.
{
"options": {},
"indexes": [
{
"v": 2,
"key": {
"_id": 1
},
"name": "_id_",
"ns": "demo.item"
},
{
"v": 2,
"key": {
"itemId": 1.0
},
"name": "itemId_1",
"ns": "demo.item"
}
],
"uuid": "8ce4755612da4d048b0fd38a793f2b55"
}
And here is the script I use to do the conversion.
Questions:
Why mongorestore does not accept the dumped file created by mongodump?
Is there any method for avoiding from modifying the dumped files manually?

Answer 1

You need to use mongorestore version 4.2+ that supports Extended JSON v2.0 (Canonical mode or Relaxed) format. See reference here.