在spring中使用mongodb聚合展平嵌套数组

import org.springframework.data.mongodb.core.MongoTemplate;
import org.springframework.data.mongodb.core.aggregation.Aggregation;
import org.springframework.data.mongodb.core.aggregation.AggregationResults;
import org.springframework.data.mongodb.core.aggregation.Fields;
import org.springframework.data.mongodb.core.aggregation.UnwindOperation;
import org.springframework.data.mongodb.core.query.Criteria;
import org.springframework.data.mongodb.core.query.Query;

import java.util.List;

public class Main {
    private final MongoTemplate mongoTemplate;

    public Main(MongoTemplate mongoTemplate) {
        this.mongoTemplate = mongoTemplate;
    }

    public List<FlatDocument> flattenNestedArray() {
        UnwindOperation unwindOperation = Aggregation.unwind("nestedArray");
        Aggregation aggregation = Aggregation.newAggregation(unwindOperation,
                Aggregation.project()
                        .and(Fields.UNDERSCORE_ID).as("id")
                        .and("nestedArray.field1").as("field1")
                        .and("nestedArray.field2").as("field2")
        );

        AggregationResults<FlatDocument> results = mongoTemplate.aggregate(aggregation, "collectionName", FlatDocument.class);
        return results.getMappedResults();
    }

    public static void main(String[] args) {
        // 创建MongoTemplate实例
        MongoTemplate mongoTemplate = new MongoTemplate();

        // 创建Main实例
        Main main = new Main(mongoTemplate);

        // 调用方法展平嵌套数组
        List<FlatDocument> flattenedDocuments = main.flattenNestedArray();

        // 处理展平后的文档
        for (FlatDocument document : flattenedDocuments) {
            // 处理展平后的文档
        }
    }
}