在C＃MondoDB驱动程序2中使用$ dateToString按日分组

Question

我想按天分组聚合（不是dayOfMonth或Year，只是绝对日）。因此，我想使用here $dateToString $dateToString: { format: "%Y-%m-%d", date: "$date" }所示的var groups = await collection.Aggregate() .Match(job => /*...*/) .Group(job => job.Created.ToString(), group => /*...*/) .ToListAsync(); 运算符。有没有办法为此使用表达式：

-s

我收到此错误：

  

表达式树{document} {created} .ToString ...

不支持System.DateTime类型的ToString

Answer 1

在@Blakes Seven评论的帮助下，我用另一个分组键解决了原始问题。

var groups = await collection.Aggregate()
    .Match(job => /*...*/)
    .Group(job => new 
          { 
              Year = job.Created.Year, 
              Month = job.Created.Month, 
              Day = job.Created.Day
           }, 
           group => new { Key = group.Key, Value = group.Count() })
    .ToListAsync();

修改

为了支持 day 以外的其他时段，我必须使用BsonDocument。

var groupBy = new BsonDocument
{
  {
    "_id", new BsonDocument
    {
        { "$add", new BsonArray
            {
                new BsonDocument
                {
                    { "$subtract", new BsonArray
                      {
                        new BsonDocument { { "$subtract", new BsonArray 
                          { 
                            "$created", 
                            new DateTime(0) } 
                          }   
                        new BsonDocument { { "$mod", new BsonArray  
                            {
                                new BsonDocument 
                                { 
                                  { "$subtract", new BsonArray 
                                    { 
                                      "$created", 
                                      new DateTime(0) 
                                    } 
                                  } 
                                },
                                msPerPeriod
                            }
                        } }
                      }
                    }
                },
                new DateTime(0)
            }
        }
    }
  },
  { "count", new BsonDocument("$sum", 1) } };


var groups = await collection.Aggregate()
    .Match(job => job.Created >= since && regex.IsMatch(job.Definition))
    .Group(groupBy)
    .Sort(Builders<BsonDocument>.Sort.Ascending(doc => doc["_id"]))
    .ToListAsync();

请参阅此答案：https://stackoverflow.com/a/32137234/498298