How to optimize this linq query to reduce the loops? - linq

Question

I want to optimize this query and reduce the number of loops if possible. Atleast the one where i have to select all the client id first for iteration purpose.
any help appreciated.
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

You can group invoices by ClientId and calculate all sums with this query:
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)
}
Also consider better naming. What name lst will tell to people who will read your code. If this is a list of invoices, then name it invoices. Same with promiseDates - today and tomorrow will better describe what dates stored in variables:
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
Also you can extract duplicated code into separate method:
public static decimal CalculateBalanceOn(
this IEnumerable<Invoice> invoices, DateTime date)
{
return invoices.Where(i => i.ExpDt == date).Sum(i => i.BalAmnt);
}
With all above query will look like:
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)
}