How to mass update in MongoDB after corruption - mongodb

Question

I upgraded Wekan from 0.48 to 0.95. It looks like what happened in Mongo is that it took the checklist collection from one containing a nested list of items and split it out into a new checklistItems collection. It appears to have copied the data correctly- except that instead of copying each item's title, it copied the checklist title to each list.
I started with this in wekan.checklists:
{
"_id": "z329QEDfjsuQcxz7E",
"cardId": "TBgz6gMGCcn9XNPSW",
"title": "A list",
"sort": 0,
"createdAt": {
"$date": "2018-05-09T22:20:50.537Z"
},
"items": [
{
"_id": "z329QEDfjsuQcxz7E0",
"title": "Do some stuff",
"isFinished": false,
"sort": 0
},
{
"_id": "z329QEDfjsuQcxz7E1",
"title": "Do some other stuff",
"isFinished": false,
"sort": 1
}
],
"userId": "YndMrPQ5XhZTTKD2S"
}
and wound up with the following in wekan.checklistItems:
{
"_id": "RADPEu4nhr9PgwPHH",
"title": "A list",
"sort": 0,
"isFinished": false,
"checklistId": "z329QEDfjsuQcxz7E",
"cardId": "TBgz6gMGCcn9XNPSW"
}
{
"_id": "Guy3aaJL4WLJQjzRX",
"title": "A list",
"sort": 1,
"isFinished": false,
"checklistId": "z329QEDfjsuQcxz7E",
"cardId": "TBgz6gMGCcn9XNPSW"
}
and this in wekan.checklists:
{ "_id" : "z329QEDfjsuQcxz7E", "cardId" : "TBgz6gMGCcn9XNPSW", "title" : "MVP", "sort" : 0, "createdAt" : ISODate("2018-05-09T22:20:50.537Z"), "userId" : "YndMrPQ5XhZTTKD2S" }
Is there a quick query to go back through my original wekan.checklists and update the titles in wekan.checklistItems? I note that the checklistIDs stayed the same but the card id's are different- I can of course load the old wekan.checklists collection into my current (upgraded) db to query against.

Answer 1

Fix: load your old db.checklists into db.checklistsOld (I used mongoimport -d wekan -c checklistsOld ~/checklistsOld.bson, where checklistsOld.bson held my backup from before the upgrade. Use the following script in Robo3T:
db.checklistsOld.find({}, {"_id": 1, "items.title":1, "items.sort": 1 }).forEach( (list, i, lists) => { 
  var checklistId = list._id;
  list.items.forEach( (item, j, items) => {
      var sort = item.sort,
          title = item.title;
      db.checklistItems.update({"checklistId": checklistId, "sort":sort}, {$set: {"title": title}} );
  });
});
Depending on how many items you have, you may need to adjust "shellTimeoutSec" in Robo3T (https://github.com/Studio3T/robomongo/wiki/Robomongo-Config-File-Guide)