无法隐式转换类型'System.Linq.IQueryable？

Question

这是我的代码，上面有错误

    public ActionResult  Edit(int id = 0)
    {
        KBS_Virtual_TrainingEntities db = new KBS_Virtual_TrainingEntities();
        UsersContext ctx = new UsersContext();
        UserProfile model = ctx.UserProfiles.Find(id);

        List<CourseSubscription> user_Course_subscriptions = new List<CourseSubscription>();



        foreach (UserSubscription sub in db.UserSubscriptions)
        {
            if (sub.ID == id)
            {
                user_Course_subscriptions.Add(sub.CourseSubscription);
            }
        }
        List<CourseSubscription> not_subscribe = db.CourseSubscriptions.Except(user_Course_subscriptions);

        var coursesList = from courses in not_subscribe
                          select new SelectListItem
                          {
                              Text = courses.Course.Name,
                              Value = courses.Course.ID
                              .ToString()
                          };
        var CoursesTYPE = from CourseTypes in db.CourseTypes.ToList()
                          select new SelectListItem
                          {
                              Text = CourseTypes.Name,
                              Value = CourseTypes.ID
                              .ToString()
                          };

        ViewBag.CourseID = coursesList;
        ViewBag.type = CoursesTYPE;
        return View(model);

    }

我正在尝试使用上述代码查找当前用户未订阅的课程订阅，但无法正常工作？

Answer 1

您在Except函数的结果中缺少ToList 。 像这样执行ToList ：

List<CourseSubscription> not_subscribe = db.CourseSubscriptions.Except(user_Course_subscriptions).ToList();

或者因为在您的代码中您不需要执行任何需要列表的操作，所以只需对其进行var更改或为其分配正确的类型，例如IQueryable<CourseSubscription> 。

var not_subscribe = db.CourseSubscriptions.Except(user_Course_subscriptions);