Bucketing based on whether a field exists or not - mongodb

Question

I have data that looks like this:
{ fname: "bob", age: 33, description: "brown eyes"}
{ fname: "sally", age: 20, description: "tall"}
{ fname: "jim", age: 48 }
I'm trying to, in one query, get results that look something like this:
{
hasDescription: ["bob", "sally"],
noDescription: ["jim"]
}
I've been playing around with $bucketAuto with something like this:
{
groupBy: { "$cond": [{ "$eq": [ "description", null ] }, true, false ] },
buckets: 2,
}
but am not having any success. Any guidance would be appreciated!

Answer 1

Query
group with expression on group, to make 2 groups, one that have description and one that doesnt (instead of a field to create the group, we create 2 groups based on a condtion)
the other 3 stages is to fix the structure to be like the expected output
*i don't think you need bucket, bucket is for range of values
*instead of the bellow facet could be used also, but facet is like running the aggregation 1 time per field so its slower
Playmongo (mouse to the end of each stage => see in/out of each stage)
aggregate(
[{"$group":
{"_id":
{"$cond":
[{"$ne": [{"$type": "$description"}, "missing"]}, "hasDescription",
"noDescription"]},
"names": {"$push": "$fname"}}},
{"$replaceRoot":
{"newRoot":
{"$cond":
[{"$eq": ["$_id", "noDescription"]}, {"noDescription": "$names"},
{"hasDescription": "$names"}]}}},
{"$group": {"_id": null, "docs": {"$mergeObjects": "$$ROOT"}}},
{"$replaceRoot": {"newRoot": "$docs"}}])