MongoDB $第一个不支持的错误 C# driver

Question

我在 C# driver 中有一个聚合查询，如下所示：

var result = await _records.Aggregate()
                .Match(record => record.Statuses.Any(status => status.Status == currentStatus))
                .Unwind(record => record.Statuses)
                .Sort(Builders<BsonDocument>.Sort.Descending("statuses.date"))
                .Group(doc => doc["_id"], group => new { Id = group.Key, CurrentStatus = group.First()["statuses"] })
                .Match(arg => arg.CurrentStatus["status"] == BsonValue.Create(currentStatus.ToString()))
                .ToListAsync();

匹配以下 shell 语法：

db.records.aggregate(
    [
        {
            $match : { "statuses.status" : "Finished" }
        },
        {
            $unwind: "$statuses"
        },
        {
            $sort: { "statuses.date":-1 }
        },
        {
            $group: {
                _id: "$_id",
                current_status: { $first: "$statuses" }
            }
        },
        {
            $match : { "current_status.status" : "Finished" }
        }
    ])

我认为 C# 版本因 CurrentStatus = group.First()["statuses"] 而无法正常工作，异常是：

System.NotSupportedException: get_Item of type MongoDB.Bson.BsonValue is an unsupported method in a $project or $group pipeline operator.

我对 First() 约定的方法基于此：

MongoDB C# Driver First Expression Reference

关于如何以 driver 喜欢的方式翻译它有什么想法吗？

Answer 1

在尝试了一个类似的示例之后，您似乎可以通过首先调用您的组中的 Select 来获取 statuses 字段然后调用 First() 关于：

var result = await _records.Aggregate()
  .Match(record => record.Statuses.Any(status => status.Status == currentStatus))
  .Unwind(record => record.Statuses)
  .Sort(Builders<BsonDocument>.Sort.Descending("statuses.date"))
  .Group(doc => doc["_id"], group => new 
  { 
      Id = group.Key, 
      CurrentStatus = group.Select(x => x["statuses"]).First() 
  })
  .Match(arg => arg.CurrentStatus["status"] == BsonValue.Create(currentStatus.ToString()))
  .ToListAsync();

MongoDB $第一个不支持的错误 C# driver

MongoDB $first unsupported error C# driver

c#

mongodb

aggregation-framework