MongoDB .NET Driver：如何向嵌套数组中添加元素

我要实现向嵌套多层的数组中插入元素的功能，目标数组路径为RequestMessageLog.BiDirectionalMessageLogs.RequestMessageLog.ResponseMessageLog.ResponseMessageActionLogs，对应的文档结构如下：

{
  "_id": "63206e8cc876d082460e33c3",
  "MessageTrackingId": "08eab450-a2bd-408a-afab-be9ea665503e",
  "RequestMessageLog": {
    "ResponseMessageLog": {
      "LogDateTime": "2022-09-13T11:50:36.426Z"
    },
    "LogDateTime": "2022-09-13T11:50:36.333Z",
    "StatusCode": "Success",
    "BiDirectionalMessageLogs": [
      {
        "MessageTrackingId": "bb7b5573-15ae-4db9-a67e-6862f31b9437",
        "RequestMessageLog": {
          "ResponseMessageLog": {
            "ResponseMessageActionLogs": [
              {
                "LogDateTime": "2022-09-13T11:53:42.478Z",
                "Contents": "something"
              }
            ],
            "LogDateTime": "2022-09-13T11:53:42.477Z"
          },
          "LogDateTime": "2022-09-13T11:53:42.477Z",
          "StatusCode": "Success",
          "BiDirectionalMessageLogs": null
        }
      }
    ]
  }
}

尝试的解决方案及问题 #

方法1：使用Builders构建Filter和Update #

FilterDefinition<MessageLog> filter = Builders<MessageLog>.Filter.Eq(e => e.MessageTrackingId, "08eab450-a2bd-408a-afab-be9ea665503e");
filter &= Builders<MessageLog>.Filter.Eq("RequestMessageLog.BiDirectionalMessageLogs.MessageTrackingId", "bb7b5573-15ae-4db9-a67e-6862f31b9437");

UpdateDefinition<MessageLog> update = Builders<MessageLog>.Update.Push("RequestMessageLog.BiDirectionalMessageLogs.RequestMessageLog.ResponseMessageLog.$.ResponseMessageActionLogs", responseMessageActionLog);

执行后报错：

A write operation resulted in an error. WriteError: { Category : "Uncategorized", Code : 28, Message : "Cannot create field 'RequestMessageLog' in element {BiDirectionalMessageLogs:[ { MessageTrackingId: "bb7b5573....`

方法2：使用JsonCommand执行更新 #

IMongoDatabase Database = client.GetDatabase("Logs");
var cmd = new JsonCommand<BsonDocument>(@"Database.MessageLog.update(
                            {'MessageTrackingId' : '08eab450-a2bd-408a-afab-be9ea665503e', 'RequestMessageLog.BiDirectionalMessageLogs.MessageTrackingId': '4dc1f99c-b465-4170-9fef-c78cf5e92216'},
                            {$push:{'RequestMessageLog.BiDirectionalMessageLogs.RequestMessageLog.ResponseMessageLog.$.ResponseMessageActionLogs':{'LogDateTime':'2022-09-13T11:53:42.478Z', 'Contents':'something'}}})");

Database.RunCommand(cmd);

我也参考过关于Mongo数组嵌套插入的帖子，但没法在C#中实现。请问我哪里操作有误？

问题原因及正确实现 #

你的核心错误是数组位置操作符$的使用位置错误。$只会匹配筛选条件中第一个命中的数组元素，你之前把$放在了ResponseMessageLog后，导致MongoDB误解了更新路径，试图在BiDirectionalMessageLogs数组元素下创建新的RequestMessageLog字段，这和现有文档结构冲突，因此抛出错误。

正确的Builders实现方式 #

var filter = Builders<MessageLog>.Filter.And(
    Builders<MessageLog>.Filter.Eq(e => e.MessageTrackingId, "08eab450-a2bd-408a-afab-be9ea665503e"),
    Builders<MessageLog>.Filter.Eq("RequestMessageLog.BiDirectionalMessageLogs.MessageTrackingId", "bb7b5573-15ae-4db9-a67e-6862f31b9437")
);

var update = Builders<MessageLog>.Update.Push(
    "RequestMessageLog.BiDirectionalMessageLogs.$.RequestMessageLog.ResponseMessageLog.ResponseMessageActionLogs",
    responseMessageActionLog
);

// 执行更新
var collection = Database.GetCollection<MessageLog>("MessageLog");
var result = collection.UpdateOne(filter, update);

正确的JsonCommand实现方式 #

同时修正$的位置和命令中的数据库引用错误：

IMongoDatabase Database = client.GetDatabase("Logs");
var cmd = new JsonCommand<BsonDocument>(@"db.MessageLog.update(
    {'MessageTrackingId' : '08eab450-a2bd-408a-afab-be9ea665503e', 'RequestMessageLog.BiDirectionalMessageLogs.MessageTrackingId': 'bb7b5573-15ae-4db9-a67e-6862f31b9437'},
    {$push:{'RequestMessageLog.BiDirectionalMessageLogs.$.RequestMessageLog.ResponseMessageLog.ResponseMessageActionLogs':{'LogDateTime':'2022-09-13T11:53:42.478Z', 'Contents':'something'}}}
)");

Database.RunCommand(cmd);

关键说明 #

• 将$移到BiDirectionalMessageLogs之后，MongoDB会定位到筛选条件匹配的那个数组元素，再在该元素内部的目标数组执行push操作。
• JsonCommand中需使用db.MessageLog而非Database.MessageLog，这是你之前的另一个小错误。

内容的提问来源于stack exchange，提问作者Muhammad Hamza