Find and update pairs in collection with matching and non-matching/inverse values

user_11902670 0
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I need the find matching pairs in a single collection based on the values of fields and update them.
Let's say I have the following collection:

[{ "_id": "a", "client": 1, "tag": "",  "debit": 12,  "credit": -20 },
 { "_id": "b", "client": 1, "tag": "G", "debit": -12, "credit": 20 } ,
 { "_id": "c", "client": 1, "tag": "G", "debit": 12,  "credit": 20 },
 { "_id": "d", "client": 2, "tag": "",  "debit": 13,  "credit": 0 },
 { "_id": "e", "client": 2, "tag": "G", "debit": -13, "credit": 0 },
 { "_id": "f", "client": 3, "tag": "",  "debit": 13,  "credit": 0 },
 { "_id": "g", "client": 3, "tag": "G", "debit": 14,  "credit": 0 },
 { "_id": "h", "client": 4, "tag": "",  "debit": 0,   "credit": 0 }]

Now for two documents to build a pair they have to:

  • have the same client
  • one has the "" tag, one has the "G" tag
  • one has to have the inverse value of debit OR credit
  • bonus: ignore 0 if possible (since -0 == 0, I could also just remove the field)
  • bonus: if multiple pairs with "G" are found only take one of the two

So the example collection would result in the following pairs:

  • ("a", "b") or ("a", "c"):
    • a.client == b.client && a.tag == "" && b.tag == "G" && a.debit == -b.debit
    • for "c": a.credit == -c.credit
  • ("d", "e"):
    • normal pair: d.client == e.client && d.tag == "" && e.tag == "G" && d.debit == -e.debit
  • ("f", "g") DON'T match, because 0 doesn't count
  • "h" has no match

The result could look something like this:

[{ "pair": ["a", "b"] }, { "pair": ["d", "e"] }]

The goal is to update all documents who appear in any pair, so this could also just be a list of ids.

Final goal:

[{ "_id": "a", "client": 1, "tag": "",  "debit": 12,  "credit": -20, "s": true },
 { "_id": "b", "client": 1, "tag": "G", "debit": -12, "credit": 20,  "s": true } ,
 { "_id": "c", "client": 1, "tag": "G", "debit": 12,  "credit": 20 },
 { "_id": "d", "client": 2, "tag": "",  "debit": 13,  "credit": 0,   "s": true },
 { "_id": "e", "client": 2, "tag": "G", "debit": -13, "credit": 0,   "s": true },
 { "_id": "f", "client": 3, "tag": "",  "debit": 13,  "credit": 0 },
 { "_id": "g", "client": 3, "tag": "G", "debit": 14,  "credit": 0 },
 { "_id": "h", "client": 4, "tag": "",  "debit": 0,   "credit": 0 }]

I know I can group by client but how do I group by non matching fields?
And how can I compare the values of two documents, since I have to compare each documents with all others..

In SQL I solved it with this statement, maybe this helps or makes it clearer (I know it doesn't filter duplicates, the one with duplicates is too long to get the point across):

SELECT d1.id, d2.id
FROM documents d1, documents d2
WHERE d1.client = d2.client
AND d1.tag = "" AND d2.tag = "G"
AND (d1.debit = -d2.debit OR d1.credit = -d2.credit)

Thanks :)

aggregation-framework mongodb-query mongodb
1 Answers

I hope you get a more succinct answer, but here's one way to update (using "$merge") the documents in the collection using your logic to identify them as pairs.

db.documents.aggregate([
  {
    "$match": {
      "tag": ""
    }
  },
  {
    "$set": {
      "docStore": "$$ROOT"
    }
  },
  {
    "$lookup": {
      "from": "documents",
      "localField": "client",
      "foreignField": "client",
      "let": {
        "credit": "$credit",
        "debit": "$debit",
        "tag": "$tag"
      },
      "pipeline": [
        {
          "$match": {
            "$expr": {
              "$and": [
                {"$eq": ["$tag", "G"]},
                {
                  "$or": [
                    {
                      "$and": [
                        {"$ne": ["$$credit", 0]},
                        {"$eq": [{"$add": ["$$credit", "$credit"]}, 0]}
                      ]
                    },
                    {
                      "$and": [
                        {"$ne": ["$$debit", 0]},
                        {"$eq": [{"$add": ["$$debit", "$debit"]}, 0]}
                      ]
                    }
                  ]
                }
              ]
            }
          }
        }
      ],
      "as": "pairs"
    }
  },
  {
    "$match": {
      "$expr": {
        "$gt": [{"$size": "$pairs"}, 0]
      }
    }
  },
  {
    "$set": {
      "pair": [
        "$docStore",
        {"$first": "$pairs"}
      ]
    }
  },
  {
    "$project": {
      "_id": 0,
      "pair": 1
    }
  },
  {"$unwind": "$pair"},
  {
    "$replaceWith": {
      "$mergeObjects": [
        "$pair",
        {"s": true}
      ]
    }
  },
  {"$merge": "documents"}
])

Try it on mongoplayground.net.

user_14093740
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