mongoDB : Creating An ObjectId For Each New Child Added To The Array Field -


mongodb 2.1.4(the node driver)

i'm trying create new objectid each message insert array(the array being subdocument).

i figure way - crud operations can performed on each message in array.

for example:

the "threads" collection(note- objectid each message)

{     "_id": objectid("1234132413424123"), //a thread id     messages:[         {             _id :objectid("134124412341234"),// message id             "message":"mongodb friend"          },         {             _id :objectid("534124412342377"),             "message":"mongodb friend too"          },         ...     ] }, {     "_id": objectid("22341324134224234"),     messages:[         {             _id :objectid("8341244123411235"),             "message":"something clever"          },         {             _id :objectid("134124412342376"),             "message":"blah blah blah"          },         ...     ] }

what i'm doing right now:

var query = {};  query["_id"] = new objectid(threadid);  var update = {$push: {}};    //i write update object externally aesthetics  update.$push["messages"] = newmessage;   var threadscollection = db.collection('threads'); threadscollection.findoneandupdate(query,update, function (err, result) {     if (err) {         console.log(err);     }      db.close(); });

problem:

unlike "insert" collections, update $push not create new objectid each message added array.

question:

is there standard way of creating objectid during $push child array? or should manually create objectid , add child beforehand?

not mongodb expert but, if understand correctly, wish _id field of subdocument inserted automatically.

i created threads db , inserted first message in messages collection using following command: 

db.messages.insert({messages:[{_id:objectid(), message:"message 1."}]});

notice _id:objectid() field. result follow:

enter image description here

now have objectid(56...), can update particular record , insert more messages it. , command follow: 

db.messages.update({"_id":objectid("56...")},  {$push:{messages:{_id:objectid(), message:"i message 2."}}});

and above insert new message in collection. see below screenshots:

enter image description here

and after few updates collection looks follow:

enter image description here

all _id fields in messages array automatically generated.

it might not idea use _id fields various reasons. please google more details on whether use _id key subdocuments or not.

i used mongodb shell version 3.0.6 commands.

edit 28-01-2016 16:09

since above solution based on mongodb shell, decided test using node.js driver mongodb. first of all, declare objectid variable follow

var objectid = require('mongodb').objectid;

i use objectid document id of thread message should inserted follow in update , findoneandupdate function calls

app.get('/insertnewmessage', function(req, res) {     db.collection("messages").findoneandupdate({         _id: new objectid('56aa3554e90911b64c36a424')     }, {         $push: {             messages: {                 _id: new objectid(),                 message: "from nodejs <3 using findoneandupdate.bye."             }         }     }, function(err, result) {         if (err)             res.json(err);         else             res.json(result);     }); });

tested both , works fine. see screenshot below:

enter image description here


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