如何在SpringBoot中构造与$$ROOT在mongoDB中合并的对象？

import org.springframework.data.mongodb.core.aggregation.Aggregation;
import org.springframework.data.mongodb.core.aggregation.AggregationOperation;
import import org.springframework.data.mongodb.core.aggregation.AggregationResults;
import org.springframework.data.mongodb.core.MongoTemplate;

// ...

// 创建聚合操作
AggregationOperation groupOperation = Aggregation.group().addToSet("$$ROOT").as("mergedObject");
AggregationOperation mergeOperation = Aggregation.replaceRoot().withValueOfObject("$mergedObject");

// 构建聚合管道
Aggregation aggregation = Aggregation.newAggregation(groupOperation, mergeOperation);

// 执行聚合操作
AggregationResults<Document> results = mongoTemplate.aggregate(aggregation, "collectionName", Document.class);
List<Document> mergedObjects = results.getMappedResults();

// 处理合并后的对象
for (Document mergedObject : mergedObjects) {
    // 处理合并后的对象
}