Question

我希望优化此查询并尽可能减少循环次数。至少我必须首先选择所有客户端ID以进行迭代。任何帮助表示感谢。

public DataTable convertCollectionExpectedToDatatable(List<Invoice> lst)
        {
            DataTable dtcollection = new DataTable();
            try
            {
                dtcollection.Columns.Add("ClientId", typeof(string));
                dtcollection.Columns.Add("customerName", typeof(string));
                dtcollection.Columns.Add("BalAmnt1", typeof(string));
                dtcollection.Columns.Add("BalAmnt2", typeof(string));
                dtcollection.Columns.Add("BalAmnt3", typeof(string));
                dtcollection.Columns.Add("totalAmt", typeof(string));

                DateTime promiseDate1 = DateTime.Today;
                DateTime promiseDate2 = promiseDate1.AddDays(1);
                DateTime promiseDate3 = promiseDate2.AddDays(1);

                var select = (from l in lst select l.ClientId).Distinct();
                List<long> lstInv = select.ToList<long>();

                DataRow dr;
                foreach (long inv in lstInv)
                {
                    decimal BalAmnt1 = lst.Where(Invoice => Invoice.ExpDt ==  
promiseDate1 && Invoice.ClientId == inv).Select(Invoice => Invoice.BalAmnt).Sum();
                    decimal BalAmnt2 = lst.Where(Invoice => Invoice.ExpDt == 
promiseDate2 && Invoice.ClientId == inv).Select(Invoice => Invoice.BalAmnt).Sum();
                    decimal BalAmnt3 = lst.Where(Invoice => Invoice.ExpDt == 
promiseDate3 && Invoice.ClientId == inv).Select(Invoice => Invoice.BalAmnt).Sum();

                    var clientName = (from l in lst where l.ClientId == inv select 
l.Client.Name).FirstOrDefault();

                    dr = dtcollection.NewRow();
                    dr["ClientId"] = inv.ToString();
                    dr["customerName"] = clientName.ToString();
                    dr["BalAmnt1"] = string.Format("{0:n2}", BalAmnt1);
                    dr["BalAmnt2"] = string.Format("{0:n2}", BalAmnt2);
                    dr["BalAmnt3"] = string.Format("{0:n2}", BalAmnt3);
                    dr["totalAmt"] = string.Format("{0:n2}", BalAmnt1 + BalAmnt2 + 
BalAmnt3);

                    dtcollection.Rows.Add(dr);
                }
            }

Answer 1

您可以按ClientId对发票进行分组，并使用此查询计算所有金额：

from invoice in lst
group invoice by invoice.ClientId into g
select new {
   BalAmnt1 = g.Where(i => i.ExpDt == promiseDate1).Sum(i => i.BalAmnt),
   BalAmnt2 = g.Where(i => i.ExpDt == promiseDate2).Sum(i => i.BalAmnt),
   BalAmnt3 = g.Where(i => i.ExpDt == promiseDate3).Sum(i => i.BalAmnt)
}

还要考虑更好的命名。 lst的名称将告诉将要阅读您的代码的人员。如果这是发票清单，请将其命名为invoices。与promiseDates相同 - today和tomorrow将更好地描述存储在变量中的日期：

DateTime today = DateTime.Today;
DateTime tomorrow = today.AddDays(1);
// don't know how to name dayAfterTomorrow
// suppose it has some business-specific name in your case

您还可以将重复的代码提取到单独的方法中：

public static decimal CalculateBalanceOn(
    this IEnumerable<Invoice> invoices, DateTime date)
{
    return invoices.Where(i => i.ExpDt == date).Sum(i => i.BalAmnt);
}

以上所有查询将如下所示：

from invoice in invoices
group invoice by invoice.ClientId into g
select new {
   BalanceToday = g.CalculateBalanceOn(today),
   BalanceTomorrow = g.CalculateBalanceOn(tomorrow),
   BalanceAfterTomorrow = g.CalculateBalanceOn(dayAfterTomorrow)
}

如何优化此linq查询以减少循环？

1 个答案: