Question

虽然我在MSDN和很多书中搜索过，但我找不到任何有关此类查询的帮助。也许这里有人能够帮助我。这是一个例子：

 var query = from document in Database.Documents                           
                       group document.OwnerID by 
                       new 
                       { 
                           OwnerName= document.Owner.OwnerName,
                           ReleaseDate= document.ReleaseDate,
                           OwnerID= document.OwnerID,
                           Status= document.StatusId

                       }
                       into grupo                               
                       select new AmountOfDocuments
                       {
                           OwnerName= grupo.Key.OwnerName,
                           ReleaseDate= grupo.Key.ReleaseDate,
                           OwnerID= grupo.Key.OwnerID,
                           UDocuments= grupo.Count(),
                           SDocuments= grupo.Count()
                       };

我需要让UDocuments和SDocuments分别返回状态等于U或S的文档数。我将不胜感激，但我需要弄清楚该查询本身的工作原理。

提前致谢！

Answer 1

Lambda表达式是你的朋友！

UDocuments = grupo.Where(x => x.Status == "U").Count(),
SDocuments = grupo.Where(x => x.Status == "S").Count()

编辑：没有必要在哪里。

UDocuments = grupo.Count(x => x.Status == "U"),
SDocuments = grupo.Count(x => x.Status == "S")

Answer 2

检查在Linqpad中创建的以下代码，它以两种不同的方式完成工作并产生相同的结果。第二个是优选的，因为它将Status作为值Grouping投影，因此计数变得更简单

void Main()
{
    var testList = Test.Create();

    var result = 
    testList.GroupBy(x=>new {
                          x.OwnerName,
                          x.OwnerId,
                          x.ReleaseDates
                            })
            .Select(y=>new {
                           y.Key.OwnerName,
                           y.Key.OwnerId,
                           statusU = y.Count(m=>m.status == "U"),
                           statusS = y.Count(m=>m.status == "S"),
                            });

    result.Dump();

    var result1 = 
    testList.GroupBy(x=>new {
                          x.OwnerName,
                          x.OwnerId,
                          x.ReleaseDates
                            },x=>x.status)
            .Select(y=>new {
                           y.Key.OwnerName,
                           y.Key.OwnerId,
                           statusU = y.Count(m=>m=="U"),
                           statusS = y.Count(m=>m=="S"),
                            });

    result1.Dump();
}

public class Test
{
    public string OwnerName {get; set;}

    public int OwnerId {get; set;}

    public string status {get; set;}

    public DateTime ReleaseDates{get; set;}

    public static List<Test> Create()
    {
      return new List<Test>()
        {

        new Test
        {
          OwnerName = "ABCD",
          OwnerId = 1,
          status = "S",
          ReleaseDates = DateTime.Now
        },
        new Test
        {
          OwnerName = "ABCD",
          OwnerId = 1,
          status = "S",
          ReleaseDates = DateTime.Now
        },
        new Test
        {
          OwnerName = "ABCD",
          OwnerId = 1,
          status = "S",
          ReleaseDates = DateTime.Now
        },
        new Test
        {
          OwnerName = "ABCD",
          OwnerId = 1,
          status = "U",
          ReleaseDates = DateTime.Now
        },
        new Test
        {
          OwnerName = "ABCD",
          OwnerId = 1,
          status = "U",
          ReleaseDates = DateTime.Now
        },
        new Test
        {
          OwnerName = "ABCD",
          OwnerId = 1,
          status = "S",
          ReleaseDates = DateTime.Now
        }

        };
    }   
}

GROUP“x”BY“etc”有什么作用？

2 个答案: