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c# - 如何简化我的嵌套 for 循环

问题描述

我想使用 linq 使我的代码简短而简单。

我有一个列表，其中包含leaveDates并且每个都leaveDates包含leavelist.

像这样的东西：

{ leaves_date = {07-05-2018 18:30:00}, LeaveList = {System.Collections.Generic.List<TimeClock.Model.LeaveManagementModel>} }
{ leaves_date = {08-05-2018 18:30:00}, LeaveList = {System.Collections.Generic.List<TimeClock.Model.LeaveManagementModel>} }
{ leaves_date = {21-05-2018 18:30:00}, LeaveList = {System.Collections.Generic.List<TimeClock.Model.LeaveManagementModel>} }

leaveList包含UserId, LeaveType,Status字段

现在我想要的只是计算leavedates每个状态为1并离开类型的用户的数量！= 3

我已经尝试过使用 for 循环，但我想用 linq 来做。

这是我的 for 循环代码：

for (var i = 0; i < leavesresult.Count; i++) {
    for (var a = 0; a < leavesresult[i].LeaveList.Count; a++) {
        if (leavesresult[i].LeaveList[a].status == 1.ToString() && leavesresult[i].LeaveList[a].leave_type != 3.ToString()) {
            var compair1 = leavesresult[i].LeaveList[a].user_id;
            var compair2 = attendancelist.Any(z = >z.user_id == leavesresult[i].LeaveList[a].user_id);

            if (attendancelist.Any(z = >z.user_id == leavesresult[i].LeaveList[a].user_id)) {
                int index = attendancelist.FindIndex(y = >y.user_id == leavesresult[i].LeaveList[a].user_id);

                if (leavesresult[i].LeaveList[a].check_halfday == 1) {
                    attendancelist[index].days = attendancelist[index].days
                }
                else {
                    attendancelist[index].days = attendancelist[index].days + 1;
                }
            }
            else {
                if (leavesresult[i].LeaveList[a].check_halfday == 1) {
                    attendancelist.Add(new AttendanceModel {
                        user_id = leavesresult[i].LeaveList[a].user_id,
                        days = 0.5
                    });
                }
                else {
                    attendancelist.Add(new AttendanceModel {
                        user_id = leavesresult[i].LeaveList[a].user_id,
                        days = 1
                    });
                }
            }
        }
    }
}

标签： c#linq

解决方案

我可以给你查询，你什么也学不到。而是学习如何自己进行这种转变。诀窍是不要尝试一次完成所有操作。相反，我们进行了一系列小的、明显正确的转换，每一个都让我们更接近我们的目标。

首先将内部for循环重写为foreach：

for (var i = 0; i < leavesresult.Count; i++) 
{
  foreach (var leavelist in leavesresult[i].LeaveList) 
  {
    if (leavelist.status == 1.ToString() && leavelist.leave_type != 3.ToString()) 
    {
      var compair1 = leavelist.user_id;
      var compair2 = attendancelist.Any(z => z.user_id == leavelist.user_id);
      if (attendancelist.Any(z => z.user_id == leavelist.user_id)) 
      {
        int index = attendancelist.FindIndex(y => y.user_id == leavelist.user_id);  
        if (leavelist.check_halfday == 1) 
          attendancelist[index].days = attendancelist[index].days
        else 
          attendancelist[index].days = attendancelist[index].days + 1;
      }
      else 
      {
        if (leavelist.check_halfday == 1) 
          attendancelist.Add(
            new AttendanceModel {user_id = leavelist.user_id, days = 0.5});
        else 
          attendancelist.Add(
            new AttendanceModel {user_id = leavelist.user_id, days = 1});
      }
    }
  }
}

通过该更改，您的代码已经比阅读更容易了 100 倍。

现在我们注意到一些事情：

    if (leavelist.status == 1.ToString() && leavelist.leave_type != 3.ToString())

这是写这张支票的疯狂方式。将其重写为合理的检查。

      var compair1 = leavelist.user_id;
      var compair2 = attendancelist.Any(z => z.user_id == leavelist.user_id);

这些变量都不会被读取，并且它们的初始化器是无用的。删除第二个。将第一个重命名为user_id.

        if (leavelist.check_halfday == 1) 
          attendancelist[index].days = attendancelist[index].days
        else 
          attendancelist[index].days = attendancelist[index].days + 1;

结果毫无意义。重写这个。

好的，我们现在有

for (var i = 0; i < leavesresult.Count; i++) 
{
  foreach (var leavelist in leavesresult[i].LeaveList) 
  {
    if (leavelist.status == "1" && leavelist.leave_type != "3") 
    {
      var user_id= leavelist.user_id;
      if (attendancelist.Any(z => z.user_id == leavelist.user_id)) 
      {
        int index = attendancelist.FindIndex(y => y.user_id == leavelist.user_id);  
        if (leavelist.check_halfday != 1) 
          attendancelist[index].days = attendancelist[index].days + 1;
      }
      else 
      {
        if (leavelist.check_halfday == 1) 
          attendancelist.Add(
            new AttendanceModel {user_id = leavelist.user_id, days = 0.5});
        else 
          attendancelist.Add(
            new AttendanceModel {user_id = leavelist.user_id, days = 1});
      }
    }
  }
}

在整个过程中使用辅助变量：

for (var i = 0; i < leavesresult.Count; i++) 
{
  foreach (var leavelist in leavesresult[i].LeaveList) 
  {
    if (leavelist.status == "1" && leavelist.leave_type != "3") 
    {
      var user_id = leavelist.user_id;
      if (attendancelist.Any(z => z.user_id == user_id)) 
      {
        int index = attendancelist.FindIndex(y => y.user_id == user_id);  
        if (leavelist.check_halfday != 1) 
          attendancelist[index].days = attendancelist[index].days + 1;
      }
      else 
      {
        if (leavelist.check_halfday == 1) 
          attendancelist.Add(
            new AttendanceModel {user_id = user_id, days = 0.5});
        else 
          attendancelist.Add(
            new AttendanceModel {user_id = user_id, days = 1});
      }
    }
  }
}

我们意识到 theAny和 theFindIndex正在做同样的事情。消除其中之一：

for (var i = 0; i < leavesresult.Count; i++) 
{
  foreach (var leavelist in leavesresult[i].LeaveList) 
  {
    if (leavelist.status == "1" && leavelist.leave_type != "3") 
    {
      var user_id = leavelist.user_id;
      int index = attendancelist.FindIndex(y => y.user_id == user_id);
      if (index != -1) 
      {
        if (leavelist.check_halfday != 1) 
          attendancelist[index].days = attendancelist[index].days + 1;
      }
      else 
      {
        if (leavelist.check_halfday == 1) 
          attendancelist.Add(
            new AttendanceModel {user_id = user_id, days = 0.5});
        else 
          attendancelist.Add(
            new AttendanceModel {user_id = user_id, days = 1});
      }
    }
  }
}

我们注意到我们在 final 中复制了代码if-else。唯一的区别是days：

for (var i = 0; i < leavesresult.Count; i++) 
{
  foreach (var leavelist in leavesresult[i].LeaveList) 
  {
    if (leavelist.status == "1" && leavelist.leave_type != "3") 
    {
      var user_id = leavelist.user_id;
      int index = attendancelist.FindIndex(y => y.user_id == user_id);
      if (index != -1) 
      {
        if (leavelist.check_halfday != 1) 
          attendancelist[index].days = attendancelist[index].days + 1;
      }
      else 
      {
        double days = leavelist.check_halfday == 1 ? 0.5 : 1;
        attendancelist.Add(new AttendanceModel {user_id = user_id, days = days});
      }
    }
  }
}

现在，您的代码比以前容易阅读 1000 倍。继续！将外循环重写为foreach：

foreach (var lr in leavesresult) 
{
  foreach (var leavelist in lr.LeaveList) 
  {
    if (leavelist.status == "1" && leavelist.leave_type != "3") 
    {
      var user_id = leavelist.user_id;
      int index = attendancelist.FindIndex(y => y.user_id == user_id);
      if (index != -1) 
      {
        if (leavelist.check_halfday != 1) 
          attendancelist[index].days = attendancelist[index].days + 1;
      }
      else 
      {
        double days = leavelist.check_halfday == 1 ? 0.5 : 1;
        attendancelist.Add(new AttendanceModel {user_id = user_id, days = days});
      }
    }
  }
}

我们注意到更多的事情：我们可以放入check_halfday一个解释变量，并消除days. 我们可以简化增量：

foreach (var lr in leavesresult) 
{
  foreach (var leavelist in lr.LeaveList) 
  {
    if (leavelist.status == "1" && leavelist.leave_type != "3") 
    {
      var user_id = leavelist.user_id;
      int index = attendancelist.FindIndex(y => y.user_id == user_id);
      bool halfday= leavelist.check_halfday == 1;
      if (index != -1) 
      {
        if (!halfday) 
          attendancelist[index].days += 1;
      }
      else 
      {
        attendancelist.Add(new AttendanceModel {user_id = user_id, days = halfday ? 0.5 : 1});
      }
    }
  }
}

现在我们开始将其转换为查询。要理解的关键是突变不能进入查询。突变只进入循环，从不查询。查询提出问题，它们不执行突变。

你有一个 的突变attendancelist，所以它必须保持在一个循环中。但是我们可以将所有查询逻辑移出循环，方法是认识到在内部循环中带有测试的嵌套 foreach 等效于：

var query = from lr in leaveresult
            from ll in lr.LeaveList
            where ll.status == "1"
            where ll.leave_type != "3"
            select ll;

出色的。现在我们可以在我们的 foreach 中使用它：

foreach(var ll in query) 
{
  var index = attendancelist.FindIndex(y => y.user_id == ll.user_id);
  var halfday = ll.check_halfday == 1;
  if (index != -1) 
  {
    if (!halfday) 
      attendancelist[index].days += 1;
  }
  else 
  {
    attendancelist.Add(
      new AttendanceModel {user_id = ll.user_id, days = halfday? 0.5 : 1 });
  }
}

现在我们有了这种极其简单形式的循环，我们注意到我们可以重新排序if以简化它：

foreach(var ll in query) 
{
  var index = attendancelist.FindIndex(y => y.user_id == ll.user_id);
  var halfday = ll.check_halfday == 1;
  if (index == -1) 
    attendancelist.Add(
      new AttendanceModel {user_id = ll.user_id, days = halfday? 0.5 : 1 });
  else if (!halfday) 
    attendancelist[index].days += 1;
}

我们完成了。所有的计算都是由查询完成的，所有的变化都是由 foreach 完成的，这是应该的。你的循环体现在是一个单一的、非常清晰的条件语句。

这个答案是为了回答您的问题，即如何将现有的一堆难以阅读的循环转换为易于阅读的查询。但是最好还是编写一个清楚地表达您要实现的业务逻辑的查询，我不知道那是什么。 创建您的 LINQ 查询，以便它们易于理解业务级别发生的事情。

在这种情况下，我怀疑您正在做的是维护每个用户的天数，以根据休假列表进行更新。那我们就这么写吧！

// dict[user_id] is the accumulated leave.
var dict = new Dictionary<int, double>();
var query = from lr in leaveresult
            from ll in lr.LeaveList
            where ll.status == "1"
            where ll.leave_type != "3"
            select ll;
foreach(var ll in query) 
{
  var halfday = ll.check_halfday == 1;
  if (!dict.ContainsKey(ll.user_id)) 
    dict[ll.user_id] = halfday? 0.5 : 1;
  else if (!halfday) 
    dict[ll.user_id] = dict[ll.user_id] + 1;
}

这似乎是一种比您不断搜索的列表更好的表示方式。

一旦我们达到这一点，我们就可以认识到您真正在做的是计算每个用户的总和！JamieC 的回答表明您可以使用Aggregate辅助方法来计算每个用户的总和。

但同样，这是基于您已经构建了整个机制来计算该总和的假设。再次：设计您的代码，使其清楚地按照该流程的行话实现业务流程。如果你正在做的是计算那个总和，男孩，那会不会出现在你的原始代码中。努力让你的代码在做什么更清楚。

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