Nick Schroeder Nick Schroeder - 2 months ago 6
Node.js Question

Update nested object in MongoDB if it exists, otherwise add it

I've got a json doc like this in mongoDB:

{ "_id" : ObjectId("57ed88c0965bedd2b11d5727"),
"refid" : 2,
"votes" : [
{ "ip" : "127.0.2.1", "rating" : 5 },
{ "ip" : "127.0.3.1", "rating" : 2 },
{ "ip" : "127.59.83.210", "rating" : 50 },
{ "ip" : "127.56.26.191", "rating" : 5 },
{ "ip" : "127.59.83.210", "rating" : 5 },
{ "ip" : "127.59.83.210", "rating" : 30 }
]
}


And instead of creating dupes per IP, I want to update the record found if the IP exists, or add a new entry if it doesn't. There are tons of questions on how to do similar operations, but none that I could find exactly asking something this simple. I am trying this in Node.js:

db.collection('ratings').update( { "refid":refid, "votes.ip":ip },
{
$push: { votes: { "ip":ip, "rating":rating }
}
})


But it just keeps adding new entries when I vote from the same IP.

NOTE: I am not using Mongoose.

I apologize if my question is overly elementary, I'm pretty new to MongoDB. I'm just wondering if there's a good way to do this baked in rather than iterating through every record in "votes" programmatically. Thanks!

EDIT: What I'm asking isn't currently possible, I've marked an answer below correct which contains the explanation and a link to a ticket at MongoDB for an enhancement.

As for the scenario in my question here, the code below works for me. I have no idea how good or bad it is performance wise, but it covers all of these scenarios:


  • If the record doesn't exist at all, create it

  • If the record exists, look for the IP and if found, update the rating

  • If the record exists but the IP does not, insert a new rating



Works:

db.collection('ratings').findOne({ "refid":refid }).then(function(vote) {
if (vote == null) {
newrating = {refid: refid, votes: [{ ip: ip, rating: rating }]};
db.collection('ratings').save(newrating);
} else {
db.collection('ratings').findOne({ "refid":refid, "votes.ip":ip }).then(function(rate) {
if (rate != null) {
db.collection('ratings').update(
{ refid: refid, "votes.ip" : ip },
{ $set: { "votes.$.rating" : rating } }
)
} else {
db.collection('ratings').update({"refid":refid,"votes.ip" : {$ne : ip }},
{ $push: { votes: { "ip" : ip, "rating" : rating, }}}
)
}
})
}
})

Answer

To insert a document if not exist is done by upsert and if you want to update a conditional embedded document you need $ positional operator. So you need to use both in query to implement above functionality.

But right now mongodb don't support upserting with $ positional operator

Do not use the positional operator $ with upsert operations because, inserts will use the $ as a field name in the inserted document.

So what you want is not possible to do it in one query for now, alternatively you can do it in two queries.

First

db.collection('ratings')).update(
  {"refid":refid, "votes.ip": ip},
  {
     $set: { "votes.$.rating":rating }
  }
)

It returns the number of documents updated, if it is 1 it's fine, and if it is 0 you need to push new record.

db.collection('ratings')).update( { "refid":refid, "votes.ip":{$ne: ip}},
    {$push: { votes: { "ip":ip , "rating":rating  }}
})

There also jira ticket for positional operator and upserting, plz vote for this issue if you want this functionality in mongodb. Below is the link of issue

https://jira.mongodb.org/browse/SERVER-3326