$[] operator not working in 3.6.3

[maxime...@caldera.com]

Hi,

I was looking to use the "$[]" operator in an update statement with the mongodb community edition for debian.Here is the situation :

Collection a :
{ "_id" : ObjectId("5ac74fe36b5973701b9ec7f7"), "tutu" : [ 0, 1 ] }

> a.update({}, {$inc:{"tutu.$[]":1}})
WriteResult({
        "nMatched" : 0,
        "nUpserted" : 0,
        "nModified" : 0,
        "writeError" : {
                "code" : 16837,
                "errmsg" : "cannot use the part (tutu of tutu.$[]) to traverse the element ({tutu: [ 0.0, 1.0 ]})"
        }
})

When I try the same thing in mongo 3.7.3, it works well. But the spec is written as a new feature in mongo 3.6 . Is this a mongo 3.6 bug or a mistyping in the documentation?

https://docs.mongodb.com/v3.6/reference/operator/update/positional-all/#up._S_[]

[Wan Bachtiar]

Is this a mongo 3.6 bug or a mistyping in the documentation?

Hi Maxime,

I couldn’t replicate the problem that you’re seeing on MongoDB v3.6.3:

> db.a.insert({tutu:[0, 1]});
WriteResult({
  "nInserted": 1
})
> db.a.update({}, {$inc:{"tutu.$[]":1}})
WriteResult({
  "nMatched": 1,
  "nUpserted": 0,
  "nModified": 1
})
> db.a.find()
{"_id": ObjectId("5acaafba311a74ec454207a7"), "tutu": [1,2]}

Could you check whether you're using MongoDB v3.6.3 ? 

Regards,
Wan.

​

[Maxime Alves]

Hi,

I think it is a mongo 3.6 bug.

I installed 3.6.3 on debian stretch and ubuntu xenial with the mongodb community repositories.

Thanks,
Maxime

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[maxime...@caldera.com]

Hi,

I tried with mongodb 3.6.4 from community repositories on debian, it's still not working. I'm gonna try with a clean install.

Thanks,
Maxime

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[Neil Lunn]

On Wednesday, 18 April 2018 18:50:52 UTC+10, maxime...@caldera.com wrote:

Hi,

I tried with mongodb 3.6.4 from community repositories on debian, it's still not working. I'm gonna try with a clean install.

A clean install is probably the best way.At the very least you should verify the server version with `db.version()` from the mongo shell. The error message you reported does seem indicative of a server version which is actually prior to MongoDB 3.6.