MongoDB group by values in an array field

Question

I have my asset documents in the below format.

db.asset.find({}).limit(1).pretty()
{
    \"_id\" : ObjectId(\"54e650a10364a65f62c0df4a\"),
    \"_class\" :          


        

Answer 1

You first need to unwind by the folderIds field, than group by _id and push the asset _id into a list assets_id.

db.asset.aggregate([{$unwind:"$folderIds"},  {$group:{_id: "$folderIds",assets:{$push: {assets_id:"$_id"}}}}])