具有分组依据和最大日期的Linq查询，获取Id

本文关键字：Linq 日期 查询 Id 获取 | 更新日期: 2023-09-27 18:21:56

我很难理解如何完成这个链接查询。我想获得与每个QueueNumber 的最大ProcessingStart和ProcessingComplete中的每一个相关联的Foo.Id

给定：

public class Foo
{
    public int Id { get; set; }
    public int QueueNumber { get; set; }
    public DateTime? ProcessingStart { get; set; }
    public DateTime? ProcessingComplete { get; set; }
}
public class Bar
{
    public int QueueNumber { get; set; }
    public int MaxStartId { get; set; }
    public int MaxCompleteId { get; set; }
}
public class QueryData
{
    List<Foo> Foos = new List<Foo>()
    {
        new Foo()
        {
            Id = 1,
            QueueNumber = 1,
            ProcessingStart = new DateTime(2014, 1, 1),
            ProcessingComplete = new DateTime(2014, 1, 3)
        },
        new Foo()
        {
            Id = 2,
            QueueNumber = 1,
            ProcessingStart = new DateTime(2014, 1, 2),
            ProcessingComplete = null
        },
        new Foo()
        {
            Id = 3,
            QueueNumber = 2,
            ProcessingStart = new DateTime(2014, 1, 1),
            ProcessingComplete = new DateTime (2014, 1, 2)
        },
    };
    public void GetMaxProcessingStartCompleteIdPerQueueNumber()
    {
        List<Foo> foos = Foos;
        var query = foos
            .GroupBy(gb => gb.QueueNumber)
            .Select(s => new Bar()
            {
                QueueNumber = s.Key,
                MaxStartId = s.Select(s2 => s2.Id) // select Id where Id is equal to the max ProcessingStart - Cannot implicitly convert IEnum<int> to int
                MaxCompleteId = s.Max(m => m.ProcessingComplete.Value) // select Id where Id is equal to the max ProcessingStart - Cannot implicitly convert DateTime to int
            });
    }
}

我意识到上面的两个ProcessingStart/ProcessingCOComplete作业有不同的错误，这只是我试图（但没有成功）制定所需的两个作业。

我对所提供数据的预期结果是：

Queue     MaxStartId     MaxCompletedId
-----
1     2     1
2     3     3

具有分组依据和最大日期的Linq查询，获取Id

您想要：

MaxStartId = s.First(s1 => s1.ProcessingStart == s.Max(s2 => s2.ProcessingStart)).Id,
MaxCompleteId = s.First(s1 => s1.ProcessingComplete == s.Max(m => m.ProcessingComplete.Value)).Id

这应该有效，但我会使用MaxBy方法。不为每条记录执行Max：

MaxStartId = s.MaxBy(s1 => s1.ProcessingStart).Id,
MaxCompleteId = s.MaxBy(s1 => s1.ProcessingComplete).Id
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