Mongodb sort by sum of keys -

i have json document

{    {        "_id" : objectid("5715c4bbac530eb3018b456a"),        "content_id" : "5715c4bbac530eb3018b4569",        "views" : numberlong(200),        "likes" : numberlong(100),        "comments" : numberlong(0)    },    {        "_id" : objectid("5715c4bbac530eb3018b4568"),        "content_id" : "5715c4bbac530eb3018b4567",        "views" : numberlong(300),        "likes" : numberlong(200),        "comments" : numberlong(0)    },    {        "_id" : objectid("5715c502ac530ee5018b4956"),        "content_id" : "5715c502ac530ee5018b4955",        "views" : numberlong(500),        "likes" : numberlong(0),        "comments" : numberlong(200)    } } 

how can sort document order sum("views", "likes", "comments")

something in mysql

select sum(key1, key2, key3) key document order key 

thanks in advance.

first projection obtain sum of likes, views , comments, sort based on sum. considering group content_id if needed in second snippet

db.test.aggregate([     { $project : { "_id" : "$content_id", "total" : { $add : [ "$likes", "$views", "$comments"]}}},     { $sort : { "total" : 1 }} ]) 

if need group operation if content_id can duplicated

db.test.aggregate([     { $project : { "_id" : "$content_id", "total" : { $add : [ "$likes", "$views", "$comments"]}}},     { $group : { "_id" : "$_id" , totalperid : { $sum : "$total" }}},     { $sort : { "total" : 1 }} ]) 

based on test data, get:

{ "_id" : "5715c502ac530ee5018b4955", "totalperid" : numberlong(700) } { "_id" : "5715c4bbac530eb3018b4567", "totalperid" : numberlong(500) } { "_id" : "5715c4bbac530eb3018b4569", "totalperid" : numberlong(300) }