Use array values as key in $match stage mongodb

Question

Given a list of documents like:

[
  {
    _id: 1,
    field1: "test",
    field2: "value2",
    fields: [
      "field1",
      "field2"
    ]
  },
  {
    _id: 2,
    field1: "value1",
    field2: "test",
    fields: [
      "field1",
      "field2"
    ]
  },
  {
    _id: 3,
    field1: "test",
    field2: "value2",
    fields: [
      "field2"
    ]
  },
  {
    _id: 4,
    field1: "value1",
    field2: "value2",
    fields: [
      "field1"
    ]
  },
  {
    _id: 5,
    field1: "test",
    field2: "test",
    fields: []
  }
]

I want to retrieve all documents that have any of the specified fields in the array, with a value “test”. For instance, in document with _id: 1, field2 is a value of fields array, and field2 has test as value. In contrast, document with _id: 5 has keys field1 and field2 with test value, but none of this fields is present in fields array. So, given the previous list of documents, only documents with _id: 1 and _id: 2 should be returned.

Answer 1

a possible approach as steps

1. Create a temporary key-value pair array field from the field1,field2.. so that it can be filtered/searched
2. Do the comparison using a match.
3. Remove the temporary field added in the first stage.

An approach with $anyElementTrue in the match stage - demo

db.collection.aggregate([
  {
    $addFields: {
      keyValuePairArray: {
        $filter: {
          input: { $objectToArray: "$$ROOT" },
          cond: { $not: { $in: [ "$$this.k", ["_id", "fields"] ] } }
        }
      }
    }
  },
  {
    $match: {
      $expr: {
        $anyElementTrue: {
          $map: {
            input: "$keyValuePairArray",
            in: {
              $and: [
                { $in: [ "$$this.k", "$fields" ] },
                { $eq: [ "$$this.v", "test" ] }
              ]
            }
          }
        }
      }
    }
  },
  { $unset: "keyValuePairArray" }
])

Another approach with $filter in the match stage by checking its size - demo

db.collection.aggregate([
  {
    $addFields: {
      keyValuePairArray: {
        $filter: {
          input: { $objectToArray: "$$ROOT" },
          cond: { $not: { $in: [ "$$this.k", ["_id", "fields"] ] } }
        }
      }
    }
  },
  {
    $match: {
      $expr: {
        $gt: [
          {
            $size: {
              $filter: {
                input: "$keyValuePairArray",
                cond: {
                  $and: [
                    { $in: [ "$$this.k", "$fields" ] },
                    { $eq: [ "$$this.v", "test" ] }
                  ]
                }
              }
            }
          },
          0
        ]
      }
    }
  },
  { $unset: "keyValuePairArray" }
])

EDIT - you might not even need the temporary field by removing the _id and fields since they will not affect in the $match comparison anyway - check demo

db.collection.aggregate([
  {
    $match: {
      $expr: {
        $anyElementTrue: {
          $map: {
            input: { $objectToArray: "$$ROOT" },
            in: {
              $and: [
                { $in: [ "$$this.k", "$fields" ] },
                { $eq: [ "$$this.v", "test" ] }
              ]
            }
          }
        }
      }
    }
  }
])