c# - 从列表中的 linq 查询中选择特定字段

Question

我需要优化我的 linq 查询，它看起来像这样:

List<List<Step>> steps = (from LoadTest l in monitoringTask.LoadTests
                     where (l.DateStart > (start - Core.session.timeSpanClientServer)
    && l.DateStart < (stop - Core.session.timeSpanClientServer))
                     orderby l.DateStart ascending
                     select (l.H_Scenario.Steps
                           .Where(x => x.IsActivInGlobalApdexCounting == true))
                           .ToList()).ToList();

为了优化它，我只想从我需要的类步骤中选择字段，所以我创建了类 StepDTO .

这是类 Step

 private class Step
        {
            private System.Int64 id;
            private System.Int32 responseTime;
            private H_Scenario h_Scenario;
            /other fields*/
        }

和类StepDTO

 private class StepDTO
        {
            private System.Int64 id;
            private System.Int32 responseTime;
            private H_Scenario h_Scenario;
        }

问题是如何从查询中得到List<List<StepDTO>>通过创建 StepDTO选择子句中的实例而不是选择整个 l.H_Scenario.Steps .

Answer 1

您只需要使用Select 并在其中创建新的对象实例。给你:

List<List<Step>> steps = (from LoadTest l in monitoringTask.LoadTests
                     where (l.DateStart > (start - Core.session.timeSpanClientServer)
    && l.DateStart < (stop - Core.session.timeSpanClientServer))
                     orderby l.DateStart ascending
                     select (l.H_Scenario.Steps
                               .Where(x => x.IsActivInGlobalApdexCounting == true))
                               //Here is you creating your DTO
                               .Select(x => new StepDTO 
                                     {
                                           id = x.id
                                           responseTime = x.responseTime
                                           h_Scenario = x.h_Scenario
                                     })
                               .ToList()).ToList();