EF架構~為導航屬性賦值時ToList()的替換方案

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今天在進行EF開發時，遇到一個問題，在進行join查詢時，類中的一個集合類型的導航屬性，在給它賦值時，將查詢出來的結果ToList()后，出錯了，linq to entity不支持這種操作，而在linq to sql里這是合法的，在EF中是不行的，所以，使用了替換方法，就是類型強轉，代碼如下：

 var linq = from student in base.GetModel()
                       join user_classrooms in new TsingDa_NewLearningBarRepository<User_Classroom_R>(base.UnitWork).GetModel()
                       on student.UserInfoID equals user_classrooms.UserInfoID
                       join classroom_Info in new TsingDa_NewLearningBarRepository<Classroom_Info>(base.UnitWork).GetModel()
                       on user_classrooms.ClassroomInfoID equals classroom_Info.ClassroomInfoID
                       join teacher in base.GetModel()
                       on classroom_Info.UserInfoID equals teacher.UserInfoID
                       join classroom_Plan in new TsingDa_NewLearningBarRepository<Classroom_Plan>(base.UnitWork).GetModel()
                       on user_classrooms.ClassroomInfoID equals classroom_Plan.ClassroomInfoID into list
                       join classroom_CommonValue_R in new TsingDa_NewLearningBarRepository<Classroom_CommonValue_R>(base.UnitWork).GetModel()
                       on user_classrooms.ClassroomInfoID equals classroom_CommonValue_R.ClassroomInfoID into valueList
                       join user_ClassroomPlan_Study in new TsingDa_NewLearningBarRepository<User_ClassroomPlan_Study>(base.UnitWork).GetModel()
                       .Where(i => i.ClassroomPlanID == 0 && i.StudyStatus == (int)StudyStatus.Study)

                       on new user_classroom
                       {
                           UserInfoID = student.UserInfoID,
                           ClassroomInfoID = user_classrooms.ClassroomInfoID
                       } equals new user_classroom
                       {
                           UserInfoID = user_ClassroomPlan_Study.UserInfoID,
                           ClassroomInfoID = user_ClassroomPlan_Study.ClassroomInfoID
                       } into userplane
                       let status = userplane.Count() == 0 ? (int)StudyStatus.Study : (int)StudyStatus.Finish
                       let scale = (list.Count() == 0) ? 0 : userplane.Count() - 1 / list.Count()
                       select new Classroom_Info_Ext
                       {
                           ClassroomInfoID = classroom_Info.ClassroomInfoID,
                           Title = classroom_Info.Title,
                           Type = classroom_Info.Type,
                           EndTime = user_classrooms.EndTime,
                           Student_Info = student,
                           Teacher_Info = teacher,
                           StudyScale = scale,
                           StudyStatus = (StudyStatus)status,
                           Classroom_CommonValue_R = (List<Classroom_CommonValue_R>)valueList //這里這前是valueList.ToList()
                       };

而在分頁返回時，也使用了類型轉換，這種轉換是內存中自動完成，所以性能方面不用考慮

    var result = linq.AsQueryable<Classroom_Info>().Where(spec.SatisfiedBy()).OrderBy(i => i.ClassroomInfoID);
    return new PagedList<Classroom_Info>(result, pp.PageIndex, pp.PageSize);

對於linq to entity有很多不便的地方，如在使用skip之前，必須要對iqueryable進行ordery操作；在實體賦值時不能使用邏輯判斷等等

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