MongoDB .NET：使用ArrayFilter按子文档ID更新子文档失败排查

目标是使用ArrayFilter通过子文档ID更新子文档，将指定玩家的PlayerName替换为"Josh"。已知该更新有多种实现方式，但出于学习目的选择使用ArrayFilter。

作为sanity check，若将BsonDocumentArrayFilterDefinition改为匹配PlayerName而非ID，更新可成功执行。

示例文档（精简版）：

db.Teams.find()
[
  {
    _id: ObjectId('000000000000000000002000'),
    TeamName: 'GoldDiggers',
    Players: [
      {
        _id: ObjectId('000000000000000000002001'),
        PlayerName: 'Gary',
      },
      {
        _id: ObjectId('000000000000000000002002'),
        PlayerName: 'Greg',
      },
    ]
  }
]

对应的MONGOSH命令可成功将Gary的PlayerName改为Josh：

db.Teams.updateOne(
  { _id: new ObjectId("000000000000000000002000") },
  { $set: { "Players.$[myIdentifier1].PlayerName": "Josh" } },
  {
    arrayFilters: 
    [     
      {"myIdentifier1._id": { $eq: new ObjectId("000000000000000000002001") }}
    ]
  }
)

但在C#中尝试多种ArrayFilter匹配子文档ID的写法后，均显示命令成功但未产生任何修改，相关C#代码及执行日志如下：

string myIdentifier1 = "firstIdentifier";
var filterTeam = Builders<Team>.Filter.Eq("Id", "000000000000000000002000");
var updateUsingArrayFilter = Builders<Team>.Update.Set($"Players.$[{myIdentifier1}].PlayerName", "Josh");

var arrayFilter1 = new BsonDocumentArrayFilterDefinition<BsonDocument>(
    // new BsonDocument($"{myIdentifier1}.PlayerName", new BsonDocument("$eq", "Gary"))  // Sanity check - using PlayerName instead of ID => successful update
    // new BsonDocument($"{myIdentifier1}.Id", "000000000000000000002001")
    // new BsonDocument($"{myIdentifier1}._id", "000000000000000000002001")
    // new BsonDocument($"{myIdentifier1}.Id", new BsonDocument("$eq", "000000000000000000002001"))
    new BsonDocument($"{myIdentifier1}._id", new BsonDocument("$eq", "000000000000000000002001"))
);
    
arrayFilters = new List<ArrayFilterDefinition> { arrayFilter1 };
    
updateOptions = new UpdateOptions
{
    ArrayFilters = arrayFilters
};
var result = collection.UpdateOne(filterTeam, updateUsingArrayFilter, updateOptions);

执行日志：

Command started update UpdateSubDocumentTesting { "update" : "Teams", "ordered" : true, "$db" : "UpdateSubDocumentTesting", "lsid" : { "id" : { "$binary" : { "base64" : "tFsUYfi2SLyLv1vi3JF6eg==", "subType" : "04" } } }, "updates" : [{ "q" : { "_id" : { "$oid" : "000000000000000000002000" } }, 
"u" : { "$set" : { "Players.$[firstIdentifier].PlayerName" : "Josh" } }, 
"arrayFilters" : [{ "firstIdentifier.Id" : "000000000000000000002001" }] }] }

Command started update UpdateSubDocumentTesting { "update" : "Teams", "ordered" : true, "$db" : "UpdateSubDocumentTesting", "lsid" : { "id" : { "$binary" : { "base64" : "siFCYB15RiOsqa3zB3FFSg==", "subType" : "04" } } }, "updates" : [{ "q" : { "_id" : { "$oid" : "000000000000000000002000" } }, 
"u" : { "$set" : { "Players.$[firstIdentifier].PlayerName" : "Josh" } }, 
"arrayFilters" : [{ "firstIdentifier._id" : "000000000000000000002001" }] }] }

Command started update UpdateSubDocumentTesting { "update" : "Teams", "ordered" : true, "$db" : "UpdateSubDocumentTesting", "lsid" : { "id" : { "$binary" : { "base64" : "1MjYpIlTTJGzBLQD0oa/bQ==", "subType" : "04" } } }, "updates" : [{ "q" : { "_id" : { "$oid" : "000000000000000000002000" } }, 
"u" : { "$set" : { "Players.$[firstIdentifier].PlayerName" : "Josh" } }, 
"arrayFilters" : [{ "firstIdentifier.Id" : { "$eq" : "000000000000000000002001" } }] }] }

Command started update UpdateSubDocumentTesting { "update" : "Teams", "ordered" : true, "$db" : "UpdateSubDocumentTesting", "lsid" : { "id" : { "$binary" : { "base64" : "9/5IuiFsTP6bgcLQaF5lqw==", "subType" : "04" } } }, "updates" : [{ "q" : { "_id" : { "$oid" : "000000000000000000002000" } }, 
"u" : { "$set" : { "Players.$[firstIdentifier].PlayerName" : "Josh" } }, 
"arrayFilters" : [{ "firstIdentifier._id" : { "$eq" : "000000000000000000002001" } }] }] }

所有更新尝试均返回"Command succeeded"但未修改任何数据。

问题核心是类型不匹配：MongoDB中的_id字段是ObjectId类型，而你在C#代码中直接传入字符串形式的ID，导致字符串与ObjectId无法匹配，因此找不到对应的子文档。

修改方式如下，将字符串ID转换为ObjectId类型后再传入ArrayFilter：

string myIdentifier1 = "firstIdentifier";
// 将字符串ID转换为ObjectId类型
var teamId = ObjectId.Parse("000000000000000000002000");
var filterTeam = Builders<Team>.Filter.Eq(t => t.Id, teamId);
var updateUsingArrayFilter = Builders<Team>.Update.Set($"Players.$[{myIdentifier1}].PlayerName", "Josh");

// 子文档ID同样转换为ObjectId
var playerId = ObjectId.Parse("000000000000000000002001");
var arrayFilter1 = new BsonDocumentArrayFilterDefinition<BsonDocument>(
    new BsonDocument($"{myIdentifier1}._id", new BsonDocument("$eq", playerId))
);
    
var arrayFilters = new List<ArrayFilterDefinition> { arrayFilter1 };
    
var updateOptions = new UpdateOptions
{
    ArrayFilters = arrayFilters
};
var result = collection.UpdateOne(filterTeam, updateUsingArrayFilter, updateOptions);

关键说明： #

• 使用ObjectId.Parse()将字符串ID转换为MongoDB的ObjectId类型，确保与数据库中存储的字段类型一致。
• 团队ID过滤建议使用强类型写法Eq(t => t.Id, teamId)，避免字符串字段名可能出现的大小写或映射问题（比如实体类属性是Id，但Mongo中存储为_id，虽然驱动会自动映射，但强类型写法更可靠）。

修改后，ArrayFilter就能正确匹配到目标子文档，完成更新操作。

内容的提问来源于stack exchange，提问作者Skippy VonDrake