Kotlin - Mongo DB - aggerate查询未按预期返回总和

import com.mongodb.client.MongoClients
import com.mongodb.client.MongoCollection
import com.mongodb.client.model.Aggregates
import com.mongodb.client.model.Accumulators
import org.bson.Document

fun main() {
    val client = MongoClients.create("mongodb://localhost:27017")
    val database = client.getDatabase("testdb")
    val collection: MongoCollection<Document> = database.getCollection("testcollection")

    val pipeline = listOf(
        Aggregates.match(Document("status", "active")), // 过滤条件
        Aggregates.group("$category", Accumulators.sum("totalAmount", "$amount")) // 分组并计算总和
    )

    val result = collection.aggregate(pipeline).toList()

    for (doc in result) {
        println(doc.toJson())
    }

    client.close()
}