Duplicate field name serialisation with @BsonDiscriminator and getter

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    • Type: Bug
    • Resolution: Unresolved
    • Priority: Minor - P4
    • None
    • Affects Version/s: None
    • Component/s: None
    • None
    • None
    • Java Drivers
    • Not Needed
    • None
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      Summary

      When the driver serialise a POJO annotated with @BsonDiscriminator and a getter with the readName as the discriminator key it will serialise the field two times.

      I tried with the mongo-java-driver 5.2.1.

      How to Reproduce

      Run the following code:

      public class DuplicateKeySerialization {
    public static void main(final String[] args) {
        try (
                var client = MongoClients.create(
                        MongoClientSettings.builder()
                                .applyConnectionString(
                                        new ConnectionString("<REDACTED>")
                                )
                                .serverApi(ServerApi.builder().version(ServerApiVersion.V1).build())
                                .codecRegistry(fromRegistries(
                                                getDefaultCodecRegistry(),
                                                fromProviders(PojoCodecProvider.builder().automatic(true).build())
                                        )
                                )
                                .build()
                );
        ) {
            client.getDatabase("test").getCollection("books", Book.class).insertOne(new Book());
        }
    }

    @BsonDiscriminator(key = "type", value = "BOOK")
    public static class Book {

        public String getType() {
            return "BOOK";
        }
    }
}

      Then, run the following aggregation pipeline:

      [
  {
    $project: {
      fields: {
        $objectToArray: "$$ROOT",
      },
    },
  },
]

      The output of the above pipeline is:

      {
  "_id": {
    "$oid": "67893f123f0ca25a374c252a"
  },
  "fields": [
    {
      "k": "_id",
      "v": {
        "$oid": "67893f123f0ca25a374c252a"
      }
    },
    {
      "k": "type",
      "v": "BOOK"
    },
    {
      "k": "type",
      "v": "BOOK"
    }
  ]
}

      This will cause unexpected behaviour (https://www.mongodb.com/docs/manual/core/document/#field-names) like bad projections.

            Assignee:
            Ross Lawley
            Reporter:
            Raffaele Florio
            None
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              Created:
              Updated: