将mongo聚合查询转换为kotlin

import com.mongodb.client.MongoClients
import org.bson.Document

fun main() {
    // 连接到MongoDB数据库
    val client = MongoClients.create("mongodb://localhost:27017")
    val database = client.getDatabase("mydb")
    val collection = database.getCollection("mycollection")

    // 构建聚合查询管道
    val pipeline = listOf(
        Document("\$match", Document("age", Document("\$gte", 18))),
        Document("\$group", Document("_id", "\$gender", "count", Document("\$sum", 1))),
        Document("\$sort", Document("count", -1))
    )

    // 执行聚合查询
    val result = collection.aggregate(pipeline)

    // 处理查询结果
    for (document in result) {
        val gender = document.getString("_id")
        val count = document.getInteger("count")
        println("Gender: $gender, Count: $count")
    }

    // 关闭数据库连接
    client.close()
}