Conditional grouping with $exists inside $cond

Question

I have two keys A and B and their existence in the document is mutually exclusive. I have to group by A when A exists and group by B when B exists. So I am $project

Answer 1

I found your questions while looking for a similar problem, but insted of a key, I was looking for my parameters. I finally solved the issue.

This is what I used for my $_id.status parameter, to check that if it exists inside the cond.

$cond: [{
     $or: [{
          $ne: ["$_id.status", null]
     }]
}, 1, null]

$or is not needed. I keep it there... just for fun. I don't think it affects the query that much for the moment. I will test the speed later.