MongoDB increment or insert

README.md

In mongodb it's easy to make at upsert, meaning update-or-insert by calling

db.collection.update({criteria}, {updated fields}, true)

The third parameter means - insert a new document if the document doesn't exist yet. So, for example, the following will insert a new document for the user if there's no document for that user yet, and will update it if it already exists:

 db.users.update({user_id: '1234'}, {user_id: '1234', name: 'Ran'}, true)

But What If - you want to - not insert a predefined value, but instead - increment a counter? You have a visit_count for each user, and you'd like to increment that count if there's already a document for that user's visit count, or insert 1 if it's the first time. Ideally, you'd like to do something like this:

db.users.update({user_id: '1234'}, {user_id: '1234', $inc: {visit_count: 1}}, true)

Unfortunately, however, mongo doesn't work like this. Mongo does not allow upserts in combination with $inc (or other atomic operations). Atomic operations are nice b/c you're guaranteed that the counter's (in this case counter) value will remain consistent in light of multiple concurrent updates. So how do you make an "increment if the document already exists, and insert if it doesn't"?

Here's the trick I found out yesterday (and to be fair, I'm pretty green to mongo, so maybe there's a better one). Please see the file mongo-insert-or-incr.js below.

mongo-insert-or-incr.js

var id = '1234';
db.users.insert({_id: id, visit_count: 1});
lastError = db.getLastError();
if (lastError) {
  // document already exists, so just increment the count
  db.users.update({_id: id}, {$inc: {visit_count: 1}})
}

This way you're making 2 calls on any increment you want to do. Did you find a way to do this in one call ?

Here's an update to this (very old) gist.
With mongodb today you can this this easily with a single DB call.

Example:

db.users.update({_id: id}, {
  $inc: {visit_count: 1}, 
  $set: {_id: id}
}, {upsert: true})

@rantav, thanks. Works on mongo 3.4.

@rantav Thanks. After browsing so much I finally got the answer here. This worked as expected

@rantav Thank you so much, you're a life saver. Works perfectly.

@rantav thank you very well

what if you have a document like this

{ '$inc': { totalHits: 1, 'hourly.2': 1 },
  '$setOnInsert': 
   { _id: '832bf0a3d3bece0c685e28461e3e8d88',
     trackingCode: '358CF2',
     dateTime: '2018-02-13 8',
     hitType: 'pageview',
     hourly: 
      { '0': 0,
        '1': 0,
        '2': 0,
        '3': 0
     } } }

where you want either update an hour value or insert an update. Is this possible using a single call?

This seems to work fine for me with the node.js 3.x mongodb driver:

let op = { updateOne: { filter: {name:"foo"}, update: {$inc: {"counter":10}}, upsert:true } };
await db.collection('collection-name').bulkWrite([op], {ordered:false});

If a doc with name=foo doesn't exist it creates it and sets the counter to 10. If it already exists then it adds 10 to the counter.

How to handle these two use cases using bulkWrite or findOneAndModify?

• if document does not exist then set counter to 20
• if document exists then increment counter by 1

its not working when we do multiple increment with negative value (-1.23121). it will subtract but also increase decimal value. In end you will value like 0e-14 . Any solution for this .

I am working on some kind of trading platform. So i have maintain balance of account of users. When trading happen, order are settle, at that time transactions are created very fast on same account.

So I am using $inc function to add or subtract amount from user accounts. I faced lots of issue because when i was subtracting fractional values e.g. 0.001 from 0.003 then $inc function create issue. i was not getting correct value.

Now my balance field data type is Decimal128. my previous issue was resolved but it convert value like this .e.g 1.45057300000000. if i keep subtracting amount from this balance. Mongodb convert it into
0E-14.

Anyone can help me. I want my amount maximum with 6 decimal and correct amount. if i have 0.00000001 this much balance in account then database will show me same value.

Is it possible??????

If someone help me. i will appreciate

@zsf3 : You can try setOnInsert with upsert to achieve that.

@zsf3 : You can try setOnInsert with upsert to achieve that.

Very helpful answer, thank you for that. Achieved exactly what I wanted

Yeah MongoDB (I'm using 3.6) happily starts at 0 for you if the value doesn't exist:

db.items.drop()

db.items.update({ _id: 1 }, {
  $inc: { 'counters.a': 1 }
}, { upsert: true })

// upserts:
// { "_id" : 1, "counters" : { "a" : 1 } }

db.items.update({ _id: 1 }, {
  $inc: { 'counters.b': 1 }
}, { upsert: true })

// modifies:
// { "_id" : 1, "counters" : { "a" : 1, "b" : 1 } }