How to update ~20,000 records in MongoDB with this criteria

Question

I have a MongoDB document that looks like the following:

"sport": "NFL",
"team_id": 5,
"week_num": 6,
"meta": {
   .... more data ....,
   "season_year": 2013
}

What I'd like to do is copy the season_year key/val to the "top level" document, while leaving it also embedded within the meta hash. So it would be duplicated and the end result would look like:

"sport": "NFL",
"team_id": 5,
"week_num": 6,
"season_year": 2013,
"meta": {
   .... more data ....,
   "season_year": 2013
}

Is there a trivial way to update all of the documents in my collection with the logic described above? I am using MongoDB shell version: 2.4.3

Answer 1

The problem is that during the update, you can not refer the document you are updating. So you can not achieve what you want in one query.

You need to iterate through all the documents and save them one by one:

db.yourCollection.find({}).forEach(function(doc) {
  doc.season_year = doc.meta.season_year;
  db.yourCollection.save(doc);
});