mongodb - Print a value of a mongo documents inner key -

i have document in format:

{_id:objectid("541...009b"), name:"abc" data:{"f_001":123abc, "priority":"urgent", ...},... } 

wanted write common function update key {data.f_001:0}, otherwise data remain is:

updateexistingkey("user", {name:"abc"}, "data.f_001"); 

as wasn't able achieve goal, i've tried print value, without success:

function updateexistingkey(collection, query, keyname){     db[collection].find(query).foreach(function(document) {         print(document._id)        // prints objectid("541...009b")         print(keyname)             // prints "data.f_001"         print(document.data.f_001) // prints 123abc         print(document[keyname]);  // prints undefined rather 123abc, why??     }); } 

   print(document.data.f_001) // prints 123abc    print(document[keyname]);  // prints undefined rather 123abc, why??                                                                       ^^^ 

embedded documents really embedded (i.e.: nested). not flat data structure fields having dot in them. so, dot notation might seen path allowing access field embedded in nested objects. said, both equivalent:

document.data.f_001 document["data"]["f_001"] 

but is not same as

document["data.f_001"] 

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if want update 1 arbitrary field key name, function prototype match mongodb update function (with notable exception value missing. assume here hard coded). simple wrapper need. like that:

function updateexistingkey(collection, query, keyname){     updt = {};     updt[keyname] = "somenewvalue";      db[collection].update(query,                           {$set: updt},                           {multi: true}); } 

_{untested: beware of typos !}

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if want retrieve 1 arbitrary field, might use $project operator of aggregation framework map arbitrary field name known field in output document:

function printexistingkey(collection, query, keyname){     // xxx need "keyname" validation here     // ...      db[collection].aggregate([                       {$match: query },                       {$project: { datafield: "$" + keyname }}     ]).foreach(function(d) { print(d._id); print(d.datafield); }); } 

_{untested: beware of typos !}