@Override
            public <T> BsonDocument toBsonDocument(
                    Class<T> tDocumentClass,
                    CodecRegistry codecRegistry) {
                return new BsonDocument().append("_id",
                        new BsonDocument().append("$map",
                                new BsonDocument()
                                        .append("input",
                                                new BsonDocument().append("$objectToArray",
                                                        new BsonString(
                                                                "$"
                                                                        + parentField)))
                                        .append("as", new BsonString("field"))
                                        .append("in", FIND_OBJECT_KEYS_GET_FIELD_OPERATOR)));
            }
@author James Chen
@implNote 1. We operate in an unsafe way, which means we don't check whether arguments are legal
          or not and so on 2. The publishers of mongo-java-driver are cold and the publishers of
          TurmsMongoOperations are also cold Reference:
          https://github.com/mongodb/mongo/blob/master/src/mongo/shell/utils_sh.js
turms-server-common/src/main/java/im/turms/server/common/storage/mongo/operation/TurmsMongoOperations.java