mongodb - pushing object to array attribute when updating a document -

i'm using mongoose schema & persistence layer.

when adding item array-attribute in existing document, fail: err equal null, raw equal { n: 0, nmodified: 0, ok: 1 }.

any idea why happens?

update code

 let concreteanswer = {   questionid: 1,   answer: {     rating: 34   } };  participation.update(   {     _id: 'some-unique-id',     'answers.$.instrumentname': 'some-instrument-name' // instrumentname unique within answers array   },   {     $push: {"answers.$.concreteanswers" : concreteanswer}   },   (err, raw) => {     console.log(`error occured! raw: ${raw}, error: ${err}`);   } ); 

schema definition

var participationschema = new schema({     answers: [{       instrumentname: { type: string, enum: validinstruments },       concreteanswers: [{         questionid: number,         answer: {}       }]     }]     // further attributes omitted readability }, {     timestamps: true }); var participation = mongoose.model('participation', participationschema); 

document in db

{     "_id": "some-unique-id",     "answers": [       {         "instrumentname": "some-instrument-name",         "_id": "another-unique-id",         "concreteanswers": []       },       // etc. } 

2017-04-16: changed update code according @veeram's comments:

participation.update(   {     _id: mongoose.types.objectid('some-unique-id'),     'answers.instrumentname': 'some-instrument-name'   },   {     $push: {"answers.$.concreteanswers" : concreteanswerdto}   },   // err handling above } 

i realized, operation works (i.e. doc updated in db), still execute console.log within error handling.