EF架构~为导航属性赋值时ToList()的替换方案-白红宇

今天在进行EF开发时，遇到一个问题，在进行join查询时，类中的一个集合类型的导航属性，在给它赋值时，将查询出来的结果ToList()后，出错了，linq to entity不支持这种操作，而在linq to sql里这是合法的，在EF中是不行的，所以，使用了替换方法，就是类型强转，代码如下：

var linq = from student in base.GetModel()                       join user_classrooms in new TsingDa_NewLearningBarRepository
     
      (base.UnitWork).GetModel()                       on student.UserInfoID equals user_classrooms.UserInfoID                       join classroom_Info in new TsingDa_NewLearningBarRepository
      
       (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
       
        (base.UnitWork).GetModel()                       on user_classrooms.ClassroomInfoID equals classroom_Plan.ClassroomInfoID into list                       join classroom_CommonValue_R in new TsingDa_NewLearningBarRepository
        
         (base.UnitWork).GetModel()                       on user_classrooms.ClassroomInfoID equals classroom_CommonValue_R.ClassroomInfoID into valueList                       join user_ClassroomPlan_Study in new TsingDa_NewLearningBarRepository
         
          (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
          
           )valueList //这里这前是valueList.ToList() };

而在分页返回时，也使用了类型转换，这种转换是内存中自动完成，所以性能方面不用考虑

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

对于linq to entity有很多不便的地方，如在使用skip之前，必须要对iqueryable进行ordery操作；在实体赋值时不能使用逻辑判断等等

本文转自博客园张占岭（仓储大叔）的博客，原文链接：，如需转载请自行联系原博主。