[英]Linq query with group by and max date, get Id
Having trouble wrapping my head around how to accomplish this link query. 无法解决如何完成此链接查询的问题。 I want to get the Foo.Id associated to each of the maximum ProcessingStart and ProcessingComplete, per QueueNumber
我想获取与每个QueueNumber的每个最大ProcessingStart和ProcessingComplete关联的Foo.Id
Given: 鉴于:
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
});
}
}
I realize the above two ProcessingStart/ProcessingCOmplete assignments have different errors to them, those are just the two I've tried (unsuccessfully) to craft what is needed. 我意识到上面的两个ProcessingStart / ProcessingCOmplete分配有不同的错误,它们只是我尝试(未成功)设计所需的两个。
My expected outcome with the data provided would be: 通过提供的数据,我的预期结果将是:
Queue MaxStartId MaxCompletedId
-----
1 2 1
2 3 3
You want: 你要:
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
This should work but I would use MaxBy
method instead. 这应该工作,但我会改用
MaxBy
方法。 To not perform Max
for each record: 不对每个记录执行
Max
:
MaxStartId = s.MaxBy(s1 => s1.ProcessingStart).Id,
MaxCompleteId = s.MaxBy(s1 => s1.ProcessingComplete).Id
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