MongoDB嵌套数组计数的Java实现

{
  "_id": 1,
  "name": "John",
  "scores": [
    {"subject": "Math", "score": 90},
    {"subject": "Science", "score": 85},
    {"subject": "History", "score": 95}
  ]
}

import com.mongodb.MongoClient;
import com.mongodb.client.MongoCollection;
import com.mongodb.client.MongoDatabase;
import org.bson.Document;

import java.util.Arrays;

public class MongoDBNestedArrayCount {
    public static void main(String[] args) {
        // 连接到MongoDB数据库
        MongoClient mongoClient = new MongoClient("localhost", 27017);
        MongoDatabase database = mongoClient.getDatabase("mydb");
        MongoCollection<Document> collection = database.getCollection("mycollection");

        // 创建聚合管道
        collection.aggregate(Arrays.asList(
                // 展开嵌套数组
                new Document("$unwind", "$scores"),
                // 分组并计数
                new Document("$group", new Document("_id", "$_id").append("count", new Document("$sum", 1)))
        )).forEach(document -> System.out.println(document.toJson()));

        // 关闭连接
        mongoClient.close();
    }
}