[{"category":"category1","name":"name1","price":1,"description":"description1","thumbnail":"t",},{"category":"category1","name":"name2","price":2,"description":"description2","thumbnail":"t",},{"category":"category1","name":"name3","price":3,"description":"description3","thumbnail":"t",},{"category":"category2","name":"name4","price":4,"description":"description4","thumbnail":"t",}]

db.collection.aggregate([{"$match":{"category":"category1"}},{"$count":"total"}])