Question

我正在评估我的C＃.NET Web应用程序中的性能问题，并追踪了链式lambda表达式的瓶颈。我想完全删除lambda表达式，以便我可以评估链中每个步骤的性能，但我对lambda表达式相对较新。有没有人对如何将第二个lambda express重构为更传统的代码有任何想法，以便可以跟踪每个步骤或操作？

IEnumerable<OurPerformance> validPerformances = package.TimeFilteredValidPerformances(visitDateAndTime);

IEnumerable<WebPerformance> webPerformances = performanceGroup.RegularNonPassedPerformances
            .Where(performance => validPerformances.Select(perf => perf.PerformanceId).Contains(performance.PerformanceId))                
            .Select(performance =>
                new WebPerformance
                {
                    Date = performance.PerformanceDate.ToJavaScriptDateString(),
                    PerformanceId = performance.PerformanceId,
                    Title = performance.UserFriendlyTitle,
                    ProductionSeasonId = performance.ProductionSeasonId,
                    AvailableCount = performance.AvailableCount
                });

**IEnumerable<WebProduction> webProductions = webPerformances
            .GroupBy(performance => performance.ProductionSeasonId)
            .ToDictionary(grouping => SheddProduction.GetOurProduction(grouping.Key), grouping => grouping.ToList())
            .Select(perfsByProduction =>
                new WebProduction
                {
                    ProductionSeasonId = perfsByProduction.Key.ProductionSeasonNumber,
                    Duration = perfsByProduction.Key.Duration,
                    Title = perfsByProduction.Key.UserFriendlyTitle,
                    Synopsis = perfsByProduction.Key.UserFriendlySynopsis,
                    ThumbnailImage = perfsByProduction.Key.PreviewImage,
                    Performances = perfsByProduction.Value
                });**

Answer 1

我不能建议任何算法来排除lambda表达式，但我有另一个建议。尝试使用List for webPerformances而不是IEnumerable集合。调用ToList（）获取List webPerformances。在这种情况下，第二个lambda表达式将与list一起使用，不会重新评估IEnumerable集合。

Answer 2

它实际上相当简单，将其分解为更小的部分，这些部分更明显地转化为传统的＆＃34;码。只需将每个linq表达式结果存储在一个局部变量中，如下所示：

var groupedWebPerformances = webPerformances.GroupBy(performance => performance.ProductionSeasonId);
var webPerformancesDictionary = groupedWebPerformances .ToDictionary(grouping => SheddProduction.GetOurProduction(grouping.Key), grouping => grouping.ToList());
IEnumerable<WebProduction> webProductions = webPerformancesDictionary.Select(perfsByProduction =>
                new WebProduction
                {
                    ProductionSeasonId = perfsByProduction.Key.ProductionSeasonNumber,
                    Duration = perfsByProduction.Key.Duration,
                    Title = perfsByProduction.Key.UserFriendlyTitle,
                    Synopsis = perfsByProduction.Key.UserFriendlySynopsis,
                    ThumbnailImage = perfsByProduction.Key.PreviewImage,
                    Performances = perfsByProduction.Value
                });

话虽如此，您的性能问题是您在任何地方都在使用IEnumerable。 IEnumerable每次使用时都可能会重新评估（取决于基础类型是什么），因此validPerformances会对RegularNonPassedPerformances中的每个项目以及每个项目重新评估webPerformances在整个枚举被强制评估之前，validPerformances.Select(perf => perf.PerformanceId).Contains(performance.PerformanceId)没有得到评估，所以性能问题似乎是稍后但很可能在这里：

ToList

确保在创建这些枚举时List<OurPerformance> validPerformances = package.TimeFilteredValidPerformances(visitDateAndTime).ToList(); List<WebPerformance> webPerformances = performanceGroup.RegularNonPassedPerformances .Where(performance => validPerformances.Select(perf => perf.PerformanceId).Contains(performance.PerformanceId)) .Select(performance => new WebPerformance { Date = performance.PerformanceDate.ToJavaScriptDateString(), PerformanceId = performance.PerformanceId, Title = performance.UserFriendlyTitle, ProductionSeasonId = performance.ProductionSeasonId, AvailableCount = performance.AvailableCount }) .ToList(); List<WebProduction> webProductions = webPerformances .GroupBy(performance => performance.ProductionSeasonId) .ToDictionary(grouping => SheddProduction.GetOurProduction(grouping.Key), grouping => grouping.ToList()) .Select(perfsByProduction => new WebProduction { ProductionSeasonId = perfsByProduction.Key.ProductionSeasonNumber, Duration = perfsByProduction.Key.Duration, Title = perfsByProduction.Key.UserFriendlyTitle, Synopsis = perfsByProduction.Key.UserFriendlySynopsis, ThumbnailImage = perfsByProduction.Key.PreviewImage, Performances = perfsByProduction.Value }) .ToList();强制执行$ gfortran fengdemo.F fengdemo.F:1:0: #include "fintrf.h" ^ Fatal Error: fintrf.h: No such file or directory compilation terminated.时，强制所有可枚举因素评估一次：

locate

Answer 3

这是lamba-refactoring你的第二个lambda表达式＆＃34;传统＆＃34;代码：

IEnumerable<IGrouping<string, WebProduction>> groupedPerformances 
    = webPerformances.GroupBy(performance => performance.ProductionSeasonId);

var dictionary = new Dictionary<string, List<WebProduction>>();
foreach (IGrouping<string, WebProduction> grouping in groupedPerformances)
{
    var group = new List<WebProduction>();
    foreach (WebProduction webProduction in grouping)
        group.Add(webProduction);

    dictionary.Add(grouping.Key, group);
}

var result = new List<WebProduction>();
foreach (KeyValuePair<string, List<WebProduction>> item in dictionary)
{
    var wp = new WebProduction
    {
        ProductionSeasonId = perfsByProduction.Key.ProductionSeasonNumber,
        Duration = perfsByProduction.Key.Duration,
        Title = perfsByProduction.Key.UserFriendlyTitle,
        Synopsis = perfsByProduction.Key.UserFriendlySynopsis,
        ThumbnailImage = perfsByProduction.Key.PreviewImage,
        Performances = perfsByProduction.Value
    };
    result.Add(wp);
}

我不知道你SheddProduction.GetOurProduction方法的结果类型，因此我做了一些小改动，但你可以得到要点......

消除.net lambda表达式

3 个答案: