Compare duplicates by Score By Not Max Field or Earlier Date - mongodb

Question

I need to compare duplicated documents and get the duplicated ones with the Lowest Score.
If the Score between two duplicates is Equal, then get the one with earlier date.
{
"_id": UUID("c77c72de-edd8-4576-a72c-983cf93a0f31"),
"DocumentId": "05240423067",
"Name": "John Doe",
"CreationDate": ISODate("0001-01-01T00:00:00.000+00:00"),
"Score": 5,
},
{
"_id": UUID("b5a7d404-a341-45dd-b875-864cd1e6bda2"),
"DocumentId": "05240423067",
"Name": "John Doe",
"CreationDate": ISODate("2021-07-17T00:00:00.000+00:00"),
"Score": 2
},
{
"_id": UUID("9efddd23-4b6b-4e96-ab43-b24a080107db"),
"DocumentId": "05240423067",
"Name": "John Doe",
"CreationDate": ISODate("2021-07-10T00:00:00.000+00:00"),
"Score": 2
},
{
"_id": UUID("f1a063a5-f9dd-4998-b6aa-df2071dd8677"),
"DocumentId": "88313825863",
"Name": "Marcus Joseph",
"CreationDate": ISODate("2021-07-17T00:00:00.000+00:00"),
"Score": 2
},
{
"_id": UUID("e3262f8e-bd6a-49e8-abe5-c3c1a4e49900"),
"DocumentId": "88313825863",
"Name": "Marcus Joseph",
"CreationDate": ISODate("0001-01-01T00:00:00.000+00:00"),
"Score": 1
}
Later, the resulting documents will be deleted.
Expected Result:
{
"_id": UUID("b5a7d404-a341-45dd-b875-864cd1e6bda2"),
"DocumentId": "05240423067",
"Name": "John Doe",
"CreationDate": ISODate("2021-07-17T00:00:00.000+00:00"),
"Score": 2 // Return Documents with the **Lowest Score**
},
{
"_id": UUID("9efddd23-4b6b-4e96-ab43-b24a080107db"),
"DocumentId": "05240423067",
"Name": "John Doe",
"CreationDate": ISODate("2021-07-10T00:00:00.000+00:00"),
"Score": 2 // Return Documents with the **Lowest Score**
},
{
"_id": UUID("e3262f8e-bd6a-49e8-abe5-c3c1a4e49900"),
"DocumentId": "88313825863",
"Name": "Marcus Joseph",
"CreationDate": ISODate("0001-01-01T00:00:00.000+00:00"),
"Score": 2 // If both Scores Equal, Compare CreationDate earlier
}
Mongo Version 4.2.21

Answer 1

This would be easier with some of the newer "$group" accumulators introduced in more recent versions of MongoDB, but here's one way you could do it.
db.collection.aggregate([
{
"$group": {
"_id": "$DocumentId",
"count": {"$sum": 1},
"docs": {"$push": "$$ROOT"}
}
},
{ // if only 1, keep it
"$match": {
"$expr": {"$gt": ["$count", 1]}
}
},
{ // find the doc to keep
"$set": {
"keepDoc": {
"$reduce": {
"input": "$docs",
"initialValue": {
"Score": {"$minKey": 1}
},
"in": {
"$switch": {
"branches": [
{
"case": {"$gt": ["$$this.Score", "$$value.Score"]},
"then": "$$this"
},
{
"case": {"$eq": ["$$this.Score", "$$value.Score"]},
"then": {
"$cond": [
{"$gt": ["$$this.CreationDate", "$$value.CreationDate"]},
"$$this",
"$$value"
]
}
}
],
"default": "$$value"
}
}
}
}
}
},
{ // get docs other than keepDoc
"$project": {
"_id": 0,
"expiredDocs": {
"$filter": {
"input": "$docs",
"cond": {"$ne": ["$$this", "$keepDoc"]}
}
}
}
},
{"$unwind": "$expiredDocs"},
{"$replaceWith": "$expiredDocs"}
])
Try it on mongoplayground.net.
N.B.: On mongoplayground.net, there's no easy way that I know of to enter binary UUID values in the BSON configuration, so I just used strings. It should be inconsequential to the pipeline.