MongoDB $pop element which is in 3 time nested array

Question

Here is the data structure for each document in the collection. The datastructure is fixed.

{
  '_id': 'some-timestamp',
  'RESULT': [ 
              {
               'NUMERATION': [ // numeration of divisions
                    {
                                      // numeration of producttypes
                       'DIVISIONX': [{'PRODUCTTYPE': 'product xy', COUNT: 100}] 
                    }
                ]
              }
            ]
}

The query result should be in the same structure but only contain producttypes matching a regular expression.

I tried using an nested $elemMatchoperator but this doesn't get me any closer. I don't know how I can iterate each value in the producttypes array for each division. How can I do that? Then I could apply $pop, $in and $each.

I looked at:

... and more

The solution I want to avoid is writing something like this: collection.find().forEach(function(x) { /* more for eaches */ })

Edit: Here is an example document to copy:

{"_id":"5ab550d7e85d5930b0879cbe","RESULT":[{"NUMERATION":[{"DIVISION":[{"PRODUCTTYPE":"Book","COUNT":10},{"PRODUCTTYPE":"Giftcard","COUNT":"300"}]}]}]}

E.g. the query result should only return the entry with the giftcard:

{"_id":"5ab550d7e85d5930b0879cbe","RESULT":[{"NUMERATION":[{"DIVISION":[{"PRODUCTTYPE":"Giftcard","COUNT":"300"}]}]}]}

Please post sample data set – Rahul Raj Mar 23 '18 at 16:53 — Rahul Raj, Mar 23 '18 at 16:53

Matthias Herrmann · Accepted Answer · 2018-03-23T21:56:01.187

Using the forEach approach the result is in the correct format. I'm still looking for a better way which does not involve the use of that function - therefore I will not mark this as an answer.

But for now this works fine:

db.collection.find().forEach(
    function(wholeDocument) {
        wholeDocument['RESULT'].forEach(function (resultEntry) {
                    resultEntry['NUMERATION'].forEach(function (numerationEntry) {
                        numerationEntry['DIVISION'].forEach(function(divisionEntry, index) {
                            // example condition (will be replaced by regular expression evaluation)
                            if(divisionEntry['PRODUCTTYPE'] != 'Giftcard'){
                                numerationEntry['DIVISION'].splice(index, 1);
                             }
                        })
                    })
                })
                print(wholeDocument);
    }
)

UPDATE Thanks to Rahul Raj's comments I have read up the aggregation with the $redact operator. A prototype of the solution to the issue is this query:

db.getCollection('DeepStructure').aggregate( [
  { $redact: {
                 $cond: {
                     if: { $ne: [ "$PRODUCTTYPE", "Giftcard" ] },
                     then: "$$DESCEND",
                     else: "$$PRUNE"
                 }
             }
  }
  ]
)

The only way I can think of is to come up with an aggregation query with some sort of `$redact` query on it. That might be the only way to keep the original document structure, otherwise just do projection followed by unwinding the array & then apply match conditions — Rahul Raj, Mar 23 '18 at 21:14
@RahulRaj Thanks, the `$redact` aggregation seems very promising. — Matthias Herrmann, Mar 23 '18 at 21:29

Rahul Raj · Answer 2 · 2018-03-23T19:13:19.950

I hope you're trying to update nested array. You need to use positional operators $[] or $ for that. If you use $[], you will be able to remove all matching nested array elements. And if you use $, only the first matching array element will get removed. Use $regex operator to pass on your regular expression.

Also, you need to use $pull to remove array elements based on matching condition. In your case, its regular expression. Note that $elemMatch is not the correct one to use with $pull as arguments to $pull are direct queries to the array.

db.collection.update(
 {/*additional matching conditions*/},
 {$pull: {"RESULT.$[].NUMERATION.$[].DIVISIONX":{PRODUCTTYPE: {$regex: "xy"}}}},
 {multi: true}

 )

Just replace xy with your regular expression and add your own matching conditions as required. I'm not quite sure about your data set, but I came up with the above answer based on my assumptions from the given info. Feel free to change according to your requirements.

I'm sry updating the collection is not an option. The result of the query should not be written to the database. I updated the question with an example document and result which I'm trying to accomplish. — Matthias Herrmann, Mar 23 '18 at 19:38

MongoDB $pop element which is in 3 time nested array

2 Answers2