[{"sellerId":1,"rest":"test"},{"sellerId":2,"rest":"test"},{"sellerId":1,"rest":"test"},{"sellerId":2,"rest":"test"},{"sellerId":1,"rest":"test"},{"sellerId":2,"rest":"test"},{"sellerId":1,"rest":"test"},{"sellerId":2,"rest":"test"},{"sellerId":1,"rest":"test"},{"sellerId":2,"rest":"test"},{"sellerId":1,"rest":"test"},{"sellerId":2,"rest":"test"},]

db.collection.aggregate([{"$facet":{"counts":[{$count:"numDocs"}],"doc":[{"$match":{}}]}},{"$unwind":"$doc"},{"$unwind":"$counts"},{"$addFields":{"doc.numCount":"$counts.numDocs",}},{"$project":{counts:0}}])