c# - LINQ to Entity 查询执行时间

Question

我有这个 LINQ to Entity 查询，它可以获取大约 5000 条 Plus 记录。我注意到，返回的记录越高，执行查询和返回结果所需的时间就越多。

 lstUserAssignments =  context.UserAssessments.Where(a=>a.UserID == UserID && a.CourseID == ClassID && a.ProductID == a.ProductID && a.AppID == ApplicationID && a.IsDeleted == false && a.Score_Percentage >= 0).Select(a=> new UserAssessmentEntity()
                                          {
                                              ApplicationID = a.AppID,
                                              AttemptNo = a.AttemptNo,
                                              CourseID = a.CourseID,
                                              Score_Percentage = (float)(a.Score_Percentage != null ? a.Score_Percentage : 0),
                                              Status = a.Status,
                                              UserAssessmentID = a.UserAssessmentID,
                                              UserID = a.UserID,
                                              UserScore = a.User_Score,
                                              CreatedDateTime = a.CreatedDateTime,
                                              ModifiedDateTime = a.ModifiedDateTime,
                                              TimeSpent=a.UserAssessmentDetails.Sum(i=>i.TimeSpent??0),
                                              InstructorFeedbackText = a.UserAssessmentDetails.FirstOrDefault()!=null?a.UserAssessmentDetails.FirstOrDefault().InstructorFeedbackText:string.Empty
                                          }).ToList();

使查询简单。有 UserAssessment 和 UserAssessmentDetails 表。第一个是父母，后一个是孩子。查询中有一些性能问题，我觉得它在计算 TimeSpent 和 InstructorFeedback。谁能指出我的问题。

Answer 1

Take and Skip:
context.UserAssessments.Where(a=>a.UserID == UserID && a.CourseID == ClassID && a.ProductID == a.ProductID && a.AppID == ApplicationID && a.IsDeleted == false && a.Score_Percentage >= 0).Select(a=> new UserAssessmentEntity()
                                          {
                                              ApplicationID = a.AppID,
                                              AttemptNo = a.AttemptNo,
                                              CourseID = a.CourseID,
                                              Score_Percentage = (float)(a.Score_Percentage != null ? a.Score_Percentage : 0),
                                              Status = a.Status,
                                              UserAssessmentID = a.UserAssessmentID,
                                              UserID = a.UserID,
                                              UserScore = a.User_Score,
                                              CreatedDateTime = a.CreatedDateTime,
                                              ModifiedDateTime = a.ModifiedDateTime,
                                              TimeSpent=a.UserAssessmentDetails.Sum(i=>i.TimeSpent??0),
                                              InstructorFeedbackText = a.UserAssessmentDetails.FirstOrDefault()!=null?a.UserAssessmentDetails.FirstOrDefault().InstructorFeedbackText:string.Empty
                                          }).Take(10).Skip(10).ToList();