Question

我最近编写了一个LINQ查询，以获取包含过去6个月展示位置金额的Dictionary。

它返回Dictionary月份字符串 - 十进制金额对。

这似乎是一种喧嚣。你们中的任何一位LINQ大师都能帮我重构一下以使它更干净一点吗？

/// <summary>
/// Gets the last 6 months of Placement History totalled by Month 
/// for all Agencies
/// </summary>
/// <returns></returns>
public Dictionary<string, decimal> getRecentPlacementHistory()
{
    var placementHistoryByMonth = new Dictionary<string, decimal>();

    using (DemoLinqDataContext db = new DemoLinqDataContext())
    {
        for (int i = 0; i < 6; i++)
        {
            Decimal monthTotal = 
              (from a in db.Accounts
               where 
                 (a.Date_Assigned.Value.Month == DateTime.Now.AddMonths(-i).Month &&
                  a.Date_Assigned.Value.Year == DateTime.Now.AddMonths(-i).Month)
               select a.Amount_Assigned).Sum();
            String currentMonth = DateTime.Now.AddMonths(-i).ToString("MMM");

            placementHistoryByMonth.Add(currentMonth, monthTotal);
        }
        return placementHistoryByMonth;
    }
}

Answer 1

第一个问题：

where (a.Date_Assigned.Value.Month == DateTime.Now.AddMonths(-i).Month &&
       a.Date_Assigned.Value.Year == DateTime.Now.AddMonths(-i).Month)

后面的表达不应该以.Year而不是.Month结束吗？当然，你很少会得到一年的价值为1-12 ......

我会提取“当前月份”的想法，因为你经常使用它。请注意，您还要多次使用当前时间，如果它在月底的午夜运行，可能会产生奇怪的结果......

public Dictionary<string, decimal> getRecentPlacementHistory()
{
    var placementHistoryByMonth = new Dictionary<string, decimal>();
    using (DemoLinqDataContext db = new DemoLinqDataContext())
    {
        DateTime now = DateTime.Now;

        for (int i = 0; i < 6; i++)
        {
            DateTime selectedDate = now.AddMonths(-i);

            Decimal monthTotal = 
               (from a in db.Accounts
                where (a.Date_Assigned.Value.Month == selectedDate.Month &&
                       a.Date_Assigned.Value.Year == selectedDate.Year)
                select a.Amount_Assigned).Sum();

            placementHistoryByMonth.Add(selectedDate.ToString("MMM"),
                                        monthTotal);
        }
        return placementHistoryByMonth;
    }
}

我意识到这可能是你试图摆脱的循环。您可以尝试计算整批日期的上限和下限，然后在相关范围内按a.Date_Assigned的年/月进行分组。说实话，它并不会更漂亮。请注意，如果您可以将其关闭，那只会对数据库进行一次查询。

Answer 2

使用分组依据

DateTime now = DateTime.Now;
DateTime thisMonth = new DateTime(now.Year, now.Month, 1);

Dictionary<string, decimal> dict;
using (DemoLinqDataContext db = new DemoLinqDataContext())
{
    var monthlyTotal = from a in db.Accounts
        where a.Date_Assigned > thisMonth.AddMonths(-6)
        group a by new {a.Date_Assigned.Year, a.Date_Assigned.Month} into g
        select new {Month = new DateTime(g.Key.Year, g.Key.Month, 1),
                    Total = g.Sum(a=>a.Amount_Assigned)};

    dict = monthlyTotal.OrderBy(p => p.Month).ToDictionary(n => n.Month.ToString("MMM"), n => n.Total);
}

不需要循环！

Answer 3

如果您不担心没有数据而缺少月份，那么我遇到了类似的问题，我做了以下操作:(翻译成您的变量）

  DateTime startPeriod = 
     new DateTime(DateTime.Now.Year, DateTime.Now.Month, 1).AddMonths(-6);

  var query1 = from a in db.Accounts where a.Date_Assigned >= startPeriod
 group a by new { a.Date_Assigned.Year  ,a.Date_Assigned.Month  } into result
 select new
 {
     dt = new DateTime( result.Key.Year, result.Key.Month , 1),
     MonthTotal = result.Sum(i => i.Amount_Assigned)
 } ;             

  var dict = query1.OrderBy(p=> p.dt).ToDictionary(n => n.Dt.ToString("MMM") , n => n.MonthTotal );

如何使这个LINQ查询更干净？

3 个答案: