How to move documents in mongodb between collections

Question

How can I move one existing document from one collection to another?

Basically, what I have, is a customer Schema:

const customerSchema = new mongoose.Schema ({
    firstname: String,
    lastname: String,
    email: String,
});

and the Model for it:

const Customer = new mongoose.model('Customer', customerSchema);

Now I want to move one document to an archive collection. So I thought, I create a new model, like so:

const CustomerArchive = new mongoose.model('CustomerArchive', customerSchema);

Then, when someone clicks on a Button with the formaction: "/archive-data", the dataset needs to be moved from the Customer collection to the CustomerArchive collection.

  {
    _id: new ObjectId("6325ba96f228119e479963ca"),
    firstname: 'Testuser',
    lastname: 'Testuser',
    email: 'test@user',
    __v: 0
  }

Is there a way to move that one document to another collection without defining each attribute again?

app.post("/archive-data", (req, res) => {
    const docId = req.body.archiveButton;

    Customer.find({ _id: docId }, (err, document) => {
        CustomerArchive.create([document])
    })

})

This is what I have so far, it does work, but there has to be better way - even when it comes to unique IDs or duplicates:

app.post("/archive-data", (req, res) => {
    const docId = req.body.archiveButton;

    Customer.find({ _id: docId}, (err, document) => {
        CustomerArchive.create({
            _id: document[0]._id,
            firstname: document[0].firstname,
            lastname: document[0].lastname,
            email: document[0].email
        });
        Customer.findByIdAndRemove(docId, (err) => {
            if (!err) {
                res.redirect("/customers");
            } else {
                console.log(err);
            }
        });
    })
});

When doing this another problem might arise. Let's assume I move a document from Customer collection to an archive collection. But what, if someone decides to move the archived document back to the Customer collection - the chances that the id already exists might be very low, but within a huge customer db it might happen.

considering your 2nd question about ids across collections. I have found this. https://stackoverflow.com/questions/5303869/mongodb-are-mongo-ids-unique-across-collections so ids are unique only to their collection. — Fiehra, Sep 18 '22 at 11:13
Why do you want to keep the _id the same as before? couldnt you just insert a new document with a normal Document.save() and let it assign a new unique id but with the old values for name, email etc — Fiehra, Sep 18 '22 at 11:16
at the current state I am at your point, where it wouldnt matter to assing a new id - but what if you connect data to your customers id - then you wont lose this connection, just because you move them to the archive or something like that — VebDav, Sep 19 '22 at 18:18

score 1 · Answer 1 · answered Sep 18 '22 at 11:17

You can simply write a short aggregation pipeline like this:

app.post("/archive-data", async (req, res) => {
    const docId = req.body.archiveButton;

    await Customer.aggregate([
     { $match: 
       { _id: docId}
     }, 
     {
       $merge: {
          into: "customerArchive",
          on: "_id",
          whenMatched: "replace",
          whenNotMatched: "insert"
       }
     }
     ]).exec((err, res) => console.log(`${err} ${res}`));
    Customer.findByIdAndRemove(docId, (err) => {
            if (!err) {
                res.redirect("/customers");
            } else {
                console.log(err);
            }
    });
});

In the pipeline, we first match the required document and merge it into the customerArchive collection using $merge.

If you are using ObjectId, as recommended by Mongodb, you can be sure that it will be unique across collections, as it is a combination of timestamp, a random number, and an auto-incrementing counter, hence the chances of collisions are highly unlikely.

Also, creating a new collection to store just archive customers, seems like overkill, you can reduce a lot of effort, by just storing a boolean value archive in the customer's collections itself, denoting whether the customer is archived or not.

Thanks for your quick response. But something is broken. The code snippet does only remove the document from the Customer collection and doesnt move the document to customerArchive — VebDav, Sep 19 '22 at 18:29
To your last point, that seems like an easier way to handle data to be archived - so you ll only filter entries without a flag. But once data grows isnt it better to keep the db small with needed data? — VebDav, Sep 19 '22 at 18:32
If you make the archive field required, within your customers' collection and index it. Then probably, the data size won't have much impact on performance. — Charchit Kapoor, Sep 20 '22 at 04:05
The aggregation seems to be working here. https://mongoplayground.net/p/h9xcmMzwx2w Is it logging any error? Try simply with `$match` stage once, and see if it's returning the matching document, if it doesn't, you might have to wrap `docId` like this `new ObjectId(docId)`. Finally what is your mongodb version? — Charchit Kapoor, Sep 20 '22 at 04:08

How to move documents in mongodb between collections

1 Answers1