Mongo push to array inside array

Question

im new with mongo and so far have no issue using it. Until i stuck at this. I need to push a document to an array inside an array. Can refer to json below.

{
    'user_id':'{1231mjnD-32JIjn-3213}',
    'name':'John',
    'campaigns':
        [
            {
                'campaign_id':3221,
                'start_date':'12-01-2012',
                'messages':
                    [
                        {
                            'message_id':211134,
                            'email':'[email protected]'
                        }
                    ]
            },
            {
                'campaign_id':3222,
                'start_date':'13-01-2012',
                'messages':
                    [
                        {
                            'message_id':315521,
                            'email':'[email protected]'
                        }
                    ]
            }
        ]
}

I want to push one document to an array of messages in a campaigns array(regardless ordering). Meaning that, i need to append new document to an array of messages. And all those messages is from inside another array or campaigns per user. Im using python so my code will be like this.

query = {"user_id" : "{1231mjnD-32JIjn-3213}", "campaigns.campaign_id": 3221}
message = {"message_id":4213122, "email":"[email protected]"}
op = {"$push" : {"campaigns.messages":message}}
mongo.TestDatabase.members.update(query, op)

There is no error upon execution. But the document seems to have no changes(no update made). What am i doing wrong here?

Remon van Vliet · Accepted Answer · 2012-02-09 12:16:10Z

9

Having arrays inside arrays is almost always a bad idea for a number of reasons. I'd put the campaigns in a dedicated collection so they become top level documents.

That said, you can push to a message array of a specific campaign through :

db.members.update(
    {"user_id" : "{1231mjnD-32JIjn-3213}", "campaigns.campaign_id": 3221},
    {$push:{"campaigns.$.messages":{"message_id":4213122, "email":"[email protected]"}}}
)

answered Feb 9, 2012 at 12:16

Remon van Vliet

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4 Comments

khairul.ikhwan Over a year ago

Thanks for the solution. It did work. Yes, i agree with you, array inside array is a bad idea. I can see it from my code now. Its a bit messy. :(

Remon van Vliet Over a year ago

Yes, and more importantly you can never edit messages without overwriting the entire array as you are not allowed to use multiple positional operators ($). Fix for this here jira.mongodb.org/browse/SERVER-831

khairul.ikhwan Over a year ago

Ahh, this is what im searching for just now. Im looking is there any way to use multiple positional operators. So its confirm that we cannot use it. Also, i get this exception : exception: can't append to array using string field name [$] code:13048 503ms. Thanks a lot. :)

Azima Over a year ago

@RemonvanVliet in this case the item is being pushed to an array. So does it require a positional operator $?

Rafiq · Accepted Answer · 2022-03-11 12:23:19Z

if you got into error mongodb The positional operator did not find the match needed from the query. then you need to use $elemMatch to select the parent array first.

await Booking.findOneAndUpdate(
              {
                _id: data.id,
                products: {
                  $elemMatch: {
                    id: product.id,
                  },
                },
              },
              {
                $push: {
                  'products.$.slots': {
                    $each: product.slots.map((slot) => {
                      return { id: slot.id, discount: slot.discount };
                    }),
                  },
                },
              },
              { new: true }
            );

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