使用 linq 和 c# 的最大父 ID 的子节点数

Posted 2023-02-16

【中文标题】使用 linq 和 c# 的最大父 ID 的子节点数

【英文标题】：number of child with max parent id with linq and c#

【发布时间】：2021-11-20 17:25:26

【问题描述】：

有什么方法可以获取具有最大父 ID 的孩子的数量并使用 linq 列出结果？ 我试图通过Status带来值的总和，但我只能从孩子那里得到最后一个 到目前为止我做了什么：

using System;
using System.Collections.Generic;
using System.Linq;

public class Program

    public static void Main()
    
        
            var lstRfq = new List<RfqEvents>()
            
                new RfqEvents(1,1,DateTime.Parse("2021-05-06 03:00:00+00"),1),
                new RfqEvents(2,2,DateTime.Parse("2021-05-06 03:00:00+00"),1),
                new RfqEvents(3,2,DateTime.Parse("2021-05-06 03:00:00+00"),1),
                new RfqEvents(4,3,DateTime.Parse("2021-05-06 00:00:00+00"),2),
                new RfqEvents(5,4,DateTime.Parse("2021-05-06 00:00:00+00"),2),
                new RfqEvents(6,5,DateTime.Parse("2021-05-06 00:00:00+00"),2),
                new RfqEvents(7,5,DateTime.Parse("2021-05-06 00:00:00+00"),2),
                new RfqEvents(8,5,DateTime.Parse("2021-05-06 00:00:00+00"),3),
                new RfqEvents(9,6,DateTime.Parse("2021-05-06 00:00:00+00"),3),
                new RfqEvents(10,6,DateTime.Parse("2021-05-06 00:00:00+00"),3),
            ;

            var subquery = from c in lstRfq
                           group c by c.RfqId into g
                           select new InternalStatusInformations
                           
                               RfqId = g.Key,
                               RfqEventId = g.Max(a => a.Id),
                               StatusId = g.Select(p => p.Status).FirstOrDefault()
                               
                           ;
            var sss = from d in lstRfq.Where(p=> subquery.Select(p=>p.RfqEventId).Contains(p.Id))
                      group d by d.Status into z
                      select new InternalStatusInformations
                      
                          StatusId = z.Key,
                          Total = z.Count(),
                          Past = z.Where(p => p.DueDate.HasValue && p.DueDate.Value.Date < DateTime.Now.Date).Count(),
                          Future = z.Where(p => p.DueDate.HasValue && p.DueDate.Value.Date > DateTime.Now.Date).Count(),
                          Today = z.Where(p => p.DueDate.HasValue && p.DueDate.Value.Date == DateTime.Now.Date).Count(),
                          FiveDays = z.Where(p => (p.DueDate.HasValue && p.DueDate.Value.Date > DateTime.Now.Date) && p.DueDate.HasValue && p.DueDate.Value.Date < DateTime.Now.Date.AddDays(5)).Count(),
                      ;

            //expected: Status 1: 2 values
            //          Status 2: 3 values
            //          Status 3: 2 value

            //output:   Status 1: 2 values
            //          Status 2: 2 values
            //          Status 3: 2 values
        
        sss.Dump();
    
            public class InternalStatusInformations
        

            public int RfqEventId  get; set; 
            public int RfqId  get; set; 
            public int StatusId  get; set; 
            public int Future  get; set; 
            public int Past  get; set; 
            public int Today  get; set; 
            public int FiveDays  get; set; 
            public int Total  get; set; 
            public DateTime? DueDate  get; set; 

        

        public class RfqEvents
        
            public RfqEvents(int id, int rfqId, DateTime? dueDate, int status)
            
                Id = id;
                RfqId = rfqId;
                DueDate = dueDate;
                Status = status;
            
            public int Id  get; set; 
            public DateTime? DueDate  get; set; 
            public int RfqId  get; set; 
            public int Status  get; set; 
        

https://dotnetfiddle.net/YoRsIG

但是结果有些不对劲，你们能帮帮我吗？

【问题讨论】：

恕我直言，您应该提供一个示例并解释您要做什么。

【参考方案1】：

如果您只想计算每个状态中不同 RfqId 值的数量，应该这样做：

var pairs = lstRfq
    .GroupBy(evt => evt.Status)
    .Select(grouping =>
        
            var status = grouping.Key;
            var count = grouping
                .Select(evt => evt.RfqId)
                .Distinct()
                .Count();
            return (status, count);
        );
foreach ((var status, var count) in pairs)

    Console.WriteLine($"Status status: count values");

输出是：

Status 1: 2 values
Status 2: 3 values
Status 3: 2 values