Great, @Thierry_Bucco - I’m glad that worked!
You could use aggregation to add the new property to all of your existing documents. I think this is a good case for
$addFields, which you can read more about in the MongoDB Manual.
If you go to Collections in the MongoDB Atlas website UI and select a collection, you’ll see an Aggregation tab above the filter bar when viewing documents in the collection. You could create an
$addFields aggregation to handle this from that part of the website. If you’re doing a more complex data transformation, you might prefer to do it in MongoDB Compass, which is a nice GUI tool for connecting to your DB and interacting with the data. The nice thing about using Compass is that you don’t have to worry about accidentally hitting the back button in your browser and losing the agg pipeline you’re working on (although maybe the website would save it in that case - I haven’t tried it). It also lets you save aggregation pipelines to use again later, and it gives you the command line commands for the agg pipeline you’re building in the GUI, so if you want to see how to do things directly from the command line, it’s a nice way to learn.