Moving data around in an aggregation stage

Working with Data
1

I am trying to rearrange the data in a stage of my aggregation pipeline as the form it is in is not what I need it to be.

Currently it is like so

foos: [
   0: {
      'code': “ABC",
      'article': DBRef(‘collection', ‘#ID1#')
   },
   1: {
      'code': “DEF",
      'article': DBRef(‘collection', '#ID2#')
   }
]
`
Whereas I need it to be like this
`
foos: {
    "ABC": "#ID1#",
    "DEF": "#ID2#"
}
`

Any pointers gratefully received
2

You might start with https://www.mongodb.com/docs/manual/reference/operator/aggregation/arrayToObject/

3

By using 2 consecutive addField stages using map I can get it so that the data is like so

foos: [
  {k: "ABC", v: "#ID1#"},
  {k: "DEF", v: "#ID2#"},
]

which is almost there but when I try to convert the foos objects into arrays with this stage

$addFields: {
  "foos": {
    $map: {
      input: "$foos",
      in: {
        $pbjectToArray: "$$this"
      }
    }
  }
}

it turns into this which is much worse seems to be converting the array into objects

foos: [
  [{"k":"k", "v":"ABC"},{"k":"v", "v":"#ID1#"}]
]
4

arrayToObject requires that my keys are k and v which they are not. How can I fix this?

5

Many thanks Peter, that looks very much like what I need. I’ll just go and try it out.

I imagine I will have to do something else to pull the Ids out of the DBRef or will that just happen?

6

Hi Edwin,
Continuing to what Peter mentioned, here is a sample query that you can try

db.collection.aggregate([
    {
        $addFields: {
            foos: {
                $arrayToObject: {
                    $map: {
                        input: "$foos",
                        as: "foo",
                        in: {
                            k: "$$foo.code",
                            v: "$$foo.article.$id"
                        }
                    }
                }
            }
        }
    }
]);
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