[{"_id":1,"results":[{race_id:1,race_name:"Monaco",points:3}]},{"_id":2,"results":[{race_id:1,race_name:"Monaco",points:5}]},{"_id":3}]

db.collection.update({_id:{$in:[1,3]}},[{$set:{results:{$ifNull:["$results",[]]}}},{$set:{results:{$concatArrays:["$results",{$filter:{input:[{_id:1,race_id:2,race_name:"Spa",points:7},{_id:3,race_id:2,race_name:"Spa",points:3}],cond:{$eq:["$$this._id","$_id"]}}}]}}},{$unset:"results._id"},{$set:{total:{$sum:"$results.points"}}}],{multi:true})