MongoDB node native driver creating duplicate documents

Question

I'm getting a duplicate document when using the mongodb-native-driver to save an update to a document. My first call to save() correctly creates the document and adds a _id with an ObjectID value. A second call creates a new document with a text _id of the original ObjectID. For example I end up with:

> db.people.find()
{ "firstname" : "Fred", "lastname" : "Flintstone", "_id" : ObjectId("52e55737ae49620000fd894e") }
{ "firstname" : "Fred", "lastname" : "Flintstone with a change", "_id" : "52e55737ae49620000fd894e" }

My first call correctly created Fred Flinstone. A second call that added " with a change" to the lastname, created a second document.

I'm using MongoDB 2.4.8 and mongo-native-driver 1.3.23.

Here is my NodeJS/Express endpoint:

app.post("/contacts", function (req, res) {
  console.log("POST /contacts, req.body: " + JSON.stringify(req.body));

  db.collection("people").save(req.body, function (err, inserted) {
    if (err) {
      throw err;
    } else {
      console.dir("Successfully inserted/updated: " + JSON.stringify(inserted));
      res.send(inserted);
    }
  });
});

Here is the runtime log messages:

POST /contacts, req.body: {"firstname":"Fred","lastname":"Flintstone"}
'Successfully inserted/updated: {"firstname":"Fred","lastname":"Flintstone","_id":"52e55737ae49620000fd894e"}'
POST /contacts, req.body: {"firstname":"Fred","lastname":"Flintstone with a change","_id":"52e55737ae49620000fd894e"}
'Successfully inserted/updated: 1'

Why doesn't my second update the existing record? Does the driver not cast the _id value to an ObjectID?

Answer 1

What you are posting back the 2nd time contains a field named "_id", and it's a string. That is the problem.

Look at the document, what the save method does is a "Simple full document replacement function". I don't use this function quit often so here's what I guess. The function use the _id field to find the document and then replace the full document with what you provided. However, what you provided is a string _id. Apparently it doesn't equal to the ObjectId. I think you should wrap it to an ObjectId before passing to the function.

Besides, the save method is not recommended according to the document. you should use update (maybe with upsert option) instead