Update an array of strings nested within an array of objects in mongodb

Question

I want to update an array of strings which is nested inside an array of Objects.

This is my Mongo document:

{
    "_id" : ObjectId("5a52d995734d1d388d17eb0b"),
    "teams" : [ 
        {
            "assignedModels" : [ 
                "5a1665a82c7eb90001a7d676", 
                "58d8fc2d734d1d5af6dd4803"
            ]
        }, 
        {
            "assignedModels" : [ 
                "58d8fc2d734d1d5af6dd4803"
            ]
        }
    ]
}

Now i want to remove "58d8fc2d734d1d5af6dd4803" string from the assignedModels of each team object.

I have already tried some queries, but nothing is working as i expected

Current query:

db.collection('organisations').updateMany(
    { _id: database.ObjectID("5a52d995734d1d388d17eb0b") ,'teams.assignedModels' : { $exists:true } },
    { $pull : {'teams.$.assignedModels' : "58d8fc2d734d1d5af6dd4803" } },
    { multi: true });

Current output:

updated the 0th element of the teams array correctly but does not traverse through the other objects.

i tried $[], teams.assignedModels as well

Expected output:

{
    "_id" : ObjectId("5a52d995734d1d388d17eb0b"),
    "teams" : [ 
        {
            "assignedModels" : [ 
                "5a1665a82c7eb90001a7d676"
            ]
        }, 
        {
            "assignedModels" : [ 
            ]
        }
    ]
}

Which version of MongoDB are you using?

dnickless
– dnickless

2018-01-17 12:06:39 +00:00
Commented Jan 17, 2018 at 12:06 — dnickless
– dnickless, Commented Jan 17, 2018 at 12:06
mongod version: 3.4.10 (MMAPv1) (Mlab)

Saiyaff Farouk
– Saiyaff Farouk

2018-01-17 12:13:28 +00:00
Commented Jan 17, 2018 at 12:13 — Saiyaff Farouk
– Saiyaff Farouk, Commented Jan 17, 2018 at 12:13

dnickless · Accepted Answer · 2018-01-17 12:21:53Z

1

In MongoDB 3.4, there is no way to do this nicely. You will need to either iterate over your elements (client-side) and update everything one-by-one. Or you could run the following query multiple times (until there are no more updates):

db.collection('organisations').updateMany(
    { _id: database.ObjectID("5a52d995734d1d388d17eb0b"), 'teams.assignedModels': "58d8fc2d734d1d5af6dd4803" },
    { $pull : {'teams.$.assignedModels' : "58d8fc2d734d1d5af6dd4803" } }
);

For MongoDB 3.6 you can simply do this:

db.collection('organisations').updateMany(
    { _id: database.ObjectID("5a52d995734d1d388d17eb0b") },
    { $pull : {'teams.$[].assignedModels' : "58d8fc2d734d1d5af6dd4803" } }
);

There's a catch, though, in case you're updating your MongoDB v3.4 to v3.6 which is documented here:

3.6 deployments have the following default featureCompatibilityVersion values: [...] For deployments upgraded from 3.4: "3.4" until you setFeatureCompatibilityVersion to "3.6".

So you will need to run the following command once to unleash the 3.6 power:

db.adminCommand( { setFeatureCompatibilityVersion: "3.6" } )

answered Jan 17, 2018 at 12:21

dnickless

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2 Comments

Eggcellentos Over a year ago

"there is no way to do this nicely" - is this still true?

dnickless Over a year ago

@ghosh: As I wrote above, for MongoDB 3.4 there is no nice way. From 3.6 onwards, this can be done nicely like I also described above.

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