db={"messages":[{"_id":ObjectId("5ef0796fdb424a92c4200cdd"),"read":[ObjectId("5ef078df7ce82f2e5cf3b586")],"content":"Test message","sender":ObjectId("5ef078df7ce82f2e5cf3b586"),"room":ObjectId("5ed4ffcdd13f45b4104a1669"),"createdAt":ISODate("2020-06-22T09:27:11.017Z"),"updatedAt":ISODate("2020-06-22T09:27:11.017Z")}],"room":[{"_id":ObjectId("5ed4ffcdd13f45b4104a1669"),"participants":[ObjectId("5ed4ffbcd13f45b4104a1667"),ObjectId("5ef078df7ce82f2e5cf3b586")],"pending":[],"name":"Global","type":"CHANNEL","creator":ObjectId("5ed4ffbcd13f45b4104a1667"),"createdAt":ISODate("2020-06-01T13:17:01.935Z"),"updatedAt":ISODate("2020-06-01T13:17:01.935Z")}]}

db.room.aggregate([{$lookup:{from:"messages",localField:"_id",foreignField:"room",as:"messages",},},{$unwind:{path:"$messages",preserveNullAndEmptyArrays:true,},},{$sort:{"messages.createdAt":-1},},{$group:{_id:"$_id",name:{$first:"$name"},type:{$first:"$type"},participants:{$first:"$participants"},latestMessage:{$first:"$messages"},createdAt:{$first:"$createdAt"},updatedAt:{$first:"$updatedAt"},unreads:{$sum:{$cond:[{$not:{$in:[ObjectId("5ef078df7ce82f2e5cf3b586"),"$messages.read"]}},0,1]}},},},])