How to transform MongoDB document to array -

my returned document looks this:

{     "_id": "57terjrtgutgsjj",     "eventlist": [         {             "eventid": "5346a816e4b0efc8bd9759b5",             "riskscore": 0,             "entity": {                 "entityid": "5346a816e4b0efc8bd9759b6",                 "name": "src ip",                 "value": "209.178.49.9",                 "type": "ip",                 "direction": "s",                 "iskey": "true"             }         }     ] } 

i want result in format:

{     "_id": "57terjrtgutgsjj",     "eventlist": [         {             "eventid": "5346a816e4b0efc8bd9759b5",             "riskscore": 0,             "entity": [                 {                     "entityid": "5346a816e4b0efc8bd9759b6",                     "name": "src ip",                     "value": "209.178.49.9",                     "type": "ip",                     "direction": "s",                     "iskey": "true"                 }             ]         }     ] } 

the difference between first , second document "entity" field simple document in first case whereas array in second case. possible convert simple document 1 of elements inside array.obviously there 1 object inside array, doesn't matter requirements.so can please tell if possible.

thanks in advance.

i question whether want , take @ positional $ operator documentation reason why nested arrays not news if want update them.

but if decide want following form suit, noting of course need obtain document content first , otherwise use $unset operator:

db.collection.find({ "_id": "57terjrtgutgsjj" }).foreach(function(doc) {     db.collection.update(         { "_id": doc._id },         { "$unset": { "entity": 1 } }     );     db.collection.update(         { "_id": doc._id },         { "$push": { "entity": doc.entity } }             );  ) 

so 1 update, no. can "bulk updates" available 2.6 release of mongodb, benefit negated way need process in bulk. applied, should able see sort of coding pattern need used.