Question 386151 in Mongodb Question posted in
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mongodb pipeline $filter with condition not $in

I want to use a pipeline to update a document by filtering on the keys of sub-documents in an object.

eg data:

{
  things: {
    a1: {},
    ...
    x1: {}
  }
}

Where "things" can contain variable keys/properties.
I know I can use an update pipeline like this, where "keepKeys" are the keys I want to keep in the "things" object:

[ 
  $set: {
    things: { 
      $arrayToObject: {
        $filter: {
          "input": {
            $objectToArray: "$$ROOT.things"
          },
          "as": "item",
          "cond": {
             "$in": [
               "$$item.k",
               keepKeys
             ]
          }
        }
     }
  } 
]

This works, but I’d rather filter out the things I don’t want as this is a much shorter list, eg where discardKeys are the keys I don’t want:

[ 
  $set: {
    things: { 
      $arrayToObject: {
        $filter: {
          "input": {
            $objectToArray: "$$ROOT.things"
          },
          "as": "item",
          "cond": {
             "$nin": [
               "$$item.k",
               discardKeys
             ]
          }
        }
     }
  } 
]

But $nin is not supported in pipeline $filter cond

Tags:

2

Answers


  1. Chosen as BEST ANSWER
    0

    This works, as per @Wernfrie Domscheit

    [ 
  $set: {
    things: { 
      $arrayToObject: {
        $filter: {
          "input": {
            $objectToArray: "$$ROOT.things"
          },
          "as": "item",
          "cond": {
            "$not": {
              "$in": [
                "$$item.k",
                discardKeys
              ]
            }
          }
        }
     }
  } 
]

  2. 0

    You can use $indexOfArray to check if the key is not present in discardKeys. Since $indexOfArray returns -1 when an element is not found.

    So if discardKeys = ["x1", "x2", "a3" ]:

    db.collection.aggregate([
  {
    $set: {
      things: {
        $arrayToObject: {
          $filter: {
            "input": {
              $objectToArray: "$$ROOT.things"
            },
            "as": "item",
            "cond": {
              $eq: [
                { $indexOfArray: [["x1", "x2", "a3"], "$$item.k"] },
                -1
              ]
            }
          }
        }
      }
    }
  }
])

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