node.js - single key value update inside array object -

i have trying update single key value array object inside mongodb collection. updates value single key value.

previous json data inside mongodb

result: [     {               "firstname": a,       "lastname": b,       "age": 5          } ]   "_id" : "582187d461cc8230bf0aba03" 

what doing updating single key value want update single key value firstname : d , need remaining value must same(persist). got changed , single key value pair updated.

 {    result: [    {              "first name":     }    ]   "_id" : "582187d461cc8230bf0aba03"   } 

both lastname , age gone. using node js update collection.

using script

  var query = {"_id" : "582187d461cc8230bf0aba03"};   var arr = [];    userobj = {    firstname : b   };    arr.push(userobj);   update = {   result : arr    };    var = options = {new : true, upsert : true};     user.findoneandupdate(query, update, options, function(err, result)   {     if(err);     console.log(err);      res.send(result);    } 

there command can update single key value , value persist in collection

yes, default when update, replace document document b.

you want use $set operator update specific fields instead of replacing entire document.

so instance if have:

{   _id: 123,   first_name: "john",   last_name: "smith",   phone_number: "(123)456-7890" } 

and do

db.user.update({_id: 123}, {first_name: "bob"}) 

you replace whole document , get:

{   _id: 123,   first_name: "bob" } 

but if do:

db.user.update({ _id: 123 }, { $set: { first_name: "bob" } }) 

you expected result of:

{   _id: 123,   first_name: "bob",   last_name: "smith",   phone_number: "(123)456-7890" } 

in case, can try this:

var obj = {   firstname: b };  user.findoneandupdate(query, {$set: obj}, options, function(err, result)