CODEWITHSUNDEEP
node.jsmongodbmongodb-query
marcel
marcel

Reputation: 3272

Single object in mongodb-collection [v 3.0.2]

I'd like to have a collection (test) to contain only one element. Therefore I have a update-query set to an empty object:

db.test.find() -> empty
var mongoData = {"name": "Biff"};
db.test.update({}, mongoData, {upsert:true}, cb);
db.test.find() -> {"name": "Biff", "_id":"1"}  

var mongoData = {"name": "Buff"}; 
db.test.update({}, mongoData, {upsert:true}, cb);
db.test.find() -> {"name": "Buff", "_id":"1"}

Why isn't it this:

db.test.find() -> empty
var mongoData = {"name": "Biff"};
db.test.update({}, mongoData, {upsert:true}, cb);
db.test.find() -> {"name": "Biff", "_id":"1"}   

var mongoData = {"name": "Buff"};
db.test.update({}, mongoData, {upsert:true}, cb);
db.test.find() -> [{"name": "Biff", "_id":"1"}, {"name": "Buff", "_id":"2"}]

Updating an empty object '{}' seems to ensure that there isn't created another element in this collection. I thought, that {} couldn't be found, so {"name":"Biff"} gets created and a _id is set to it. If I try to update {} another time, it is not creating {"name":"Biff"} again with a different _id. It is overwriting the only element in the collection. Why is this so?

Upvotes: 1

Views: 1334

Answers (2)

bagrat
bagrat

Reputation: 7428

There is no problem here as MongoDB works like that. The insert part of upsert occurs only in case if the match criteria does not hit any document:

upsert: If set to true, creates a new document when no document matches the query criteria

So in your case, the find criteria (empty document {}) matches all the documents in the collection, thus it does not insert a new document and instead updates all existing.

Upvotes: 3

Blakes Seven
Blakes Seven

Reputation: 50406

I call false on this:

Here is the code listing to prove it, if your own code differs then this should be a guide:

var async = require('async'),
    mongodb = require('mongodb'),
    MongoClient = mongodb.MongoClient;

MongoClient.connect('mongodb://localhost/test',function(err,db) {
  if (err) throw err;

  var collection = db.collection('bifftest');

  async.eachSeries(
    ["Biff","Buff"],
    function(name,callback) {
      collection.update({},{ "name": name },{ "upsert": true },callback);   
    },
    function(err) {
      if (err) throw err;

      collection.find({}).toArray(function(err,results) {
        if (err) throw err;
        console.log(results);
      });
    }
  );
});

Returns:

[ { _id: 55b8992dcc8638610dca2e7c, name: 'Buff' } ]

Just as expected.

Upvotes: 3

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