[英]EntityFramework LINQ query count fails but query returns result. How to optimize LINQ query?
我有以下執行自左外連接的 LINQ 查詢。 查詢看起來有點復雜,但只是對自身進行自連接(目的是將每個記錄與前一個工作日的記錄連接),然后進行一些參數化過濾。
var newBreakThreshold = decimal.Parse(WebConfigurationManager.AppSettings["NewBreakThreshold"]);
using (var dbContext = new NavFoToBoCompareDbContext())
{
var query = from current in dbContext.NAVSummaries
let currentWD = SqlFunctions.DatePart("dw", current.ValueDate)
let currentPD = DbFunctions.AddDays(current.ValueDate, currentWD == 2 ? -3 : currentWD == 1 ? -2 : -1).Value
join previous in dbContext.NAVSummaries
on new { current.Portfolio, PD = currentPD }
equals new { previous.Portfolio, PD = previous.ValueDate }
into previousGroup
from previous in previousGroup.DefaultIfEmpty() // LEFT OUTER JOIN
select new { outer = current, inner = previous };
if (dateStart.HasValue)
query = query.Where(e => e.outer.ValueDate >= dateStart.Value);
if (dateEnd.HasValue)
query = query.Where(e => e.outer.ValueDate <= dateEnd.Value);
if (!portfolio.Equals("ALL", StringComparison.OrdinalIgnoreCase))
query = query.Where(e => e.outer.Portfolio.Equals(portfolio, StringComparison.OrdinalIgnoreCase));
if (!owner.Equals("ALL", StringComparison.OrdinalIgnoreCase))
query = query.Where(e => e.outer.PortfolioOwner.Equals(owner, StringComparison.OrdinalIgnoreCase));
if (status != 0)
query = query.Where(e => e.outer.Statuses.Any(s => s.StatusId == status));
var query2 = query.Select(s => new
{
BackOfficeNAV = s.outer.BackOfficeNAV,
FrontOfficeNAV = s.outer.FrontOfficeNAV,
Threshold = s.outer.Threshold,
ExtractId = s.outer.ExtractId,
ExtractStatus = s.outer.ExtractStatus,
PortfolioOwner = s.outer.PortfolioOwner,
DateTimeModified = s.outer.DateTimeModified,
MostCorrectNAV = s.outer.MostCorrectNAV,
Comments = s.outer.Comments,
Statuses = s.outer.Statuses,
Extracts = s.outer.Extracts,
Portfolio = s.outer.Portfolio,
ValueDate = s.outer.ValueDate,
DifferencePercent = s.outer.DifferencePercent,
DayOverDayChange = s.outer.DifferencePercent - s.inner.DifferencePercent,
IsChange = s.inner.DifferencePercent != s.outer.DifferencePercent,
PreviousValueDate = s.inner.ValueDate,
PreviousDifferencePercent = s.inner.DifferencePercent
});
query2 = query2.Where(r => "NEW".Equals(breakOption, StringComparison.OrdinalIgnoreCase) ?
((r.DifferencePercent > r.Threshold) && r.IsChange && r.DayOverDayChange > newBreakThreshold) :
"OLD".Equals(breakOption, StringComparison.OrdinalIgnoreCase) ? (r.DifferencePercent > r.Threshold) :
"ALL".Equals(breakOption, StringComparison.OrdinalIgnoreCase));
var resultCount = query2.Count();
}
該查詢在兩個地方使用。 在一種方法中,它用於計算分頁所需的計數。 在另一種方法中,它用於從數據庫中獲取實際結果。 獲取更大結果集的實際結果的實現成功執行,而 Count() 查詢失敗並出現超時異常。 注意:兩種實現完全相同。
有人也可以幫我優化這個查詢。 提前致謝。
不太確定這就是問題所在,但至少讓我們嘗試通過手動構建具有常量值的表達式來消除dateStart
/ dateEnd
參數,從而消除所謂的參數嗅探問題的潛在影響。
首先,一個小幫手方法:
using System;
using System.Linq;
using System.Linq.Expressions;
public static class QueryableUtils
{
public static IQueryable<T> WhereBetween<T>(this IQueryable<T> source, Expression<Func<T, DateTime>> dateSelector, DateTime? startDate, DateTime? endDate)
{
if (startDate == null && endDate == null) return source;
var startCond = startDate != null ? Expression.GreaterThanOrEqual(dateSelector.Body, Expression.Constant(startDate.Value)) : null;
var endCond = endDate != null ? Expression.LessThanOrEqual(dateSelector.Body, Expression.Constant(endDate.Value)) : null;
var predicate = Expression.Lambda<Func<T, bool>>(
startCond == null ? endCond : endCond == null ? startCond : Expression.AndAlso(startCond, endCond),
dateSelector.Parameters[0]);
return source.Where(predicate);
}
}
然后嘗試以下操作,看看是否有幫助:
//if (dateStart.HasValue)
// query = query.Where(e => e.outer.ValueDate >= dateStart.Value);
//if (dateEnd.HasValue)
// query = query.Where(e => e.outer.ValueDate <= dateEnd.Value);
query = query.WhereBetween(e => e.outer.ValueDate, dateStart, dateEnd);
您可以簡單地使用 AsParallel() 來啟用 linq 查詢的多線程執行。 然后,您應該檢查表的索引以提高性能。
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