来自字段Spring Data和Mongodb的最大值

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

public class MaxValueExample {
    private MongoTemplate mongoTemplate;

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

    public int getMaxValue() {
        Aggregation aggregation = newAggregation(
            group().max("field").as("maxValue"),
            project("maxValue").andExclude("_id")
        );

        AggregationResults<MaxValueResult> result = mongoTemplate.aggregate(
            aggregation, "collectionName", MaxValueResult.class
        );

        MaxValueResult maxValueResult = result.getUniqueMappedResult();
        return maxValueResult.getMaxValue();
    }

    private static class MaxValueResult {
        private int maxValue;

        public int getMaxValue() {
            return maxValue;
        }

        public void setMaxValue(int maxValue) {
            this.maxValue = maxValue;
        }
    }
}