LINQ：无法转换类型'System.Int32'输入'System.Object的“

问题描述

我是新来的MVC和EF和LINQ。

I'm new to MVC and EF and LINQ.

我用EF和DB首先创建所有从数据库模型。我还创建了一个视图模型CourseDetailsVM：

I used EF and DB first to create all the models from the DB. I also created a ViewModel "CourseDetailsVM":

public class CourseDetailsVM
{
    public int CourseId { get; set; }
    public int CategoryFk { get; set; }
    public int SoftwareFk { get; set; }
    public int TeacherFk { get; set; }
    public string CourseCode { get; set; }
    public string CourseCodeMs { get; set; }
    public string CourseName { get; set; }
    public string CourseDescriptionShort { get; set; }
    public int CourseEventId { get; set; }
    public int? CourseEventDurationInDays { get; set; }
    public int? CourseEventPrice { get; set; }
    public int CourseEventDateId { get; set; }
    public DateTime? CourseEventDateTimeFrom { get; set; }
    public DateTime? CourseEventDateTimeTo { get; set; }
}

在我的课程控制器我尝试使用摆脱视图模型模型下面的查询（在linqpad，但不是在MVC工作），我也使用的ViewData来访问存储库（这工作正常）：

In my Course Controller I try to get the Model from the Viewmodel using the following query (which works in linqpad but not in mvc) and I also use ViewData to access the repository (this works fine):

// GET: /Course/Details/5

    public ActionResult Details(int id)
    {
        // get courses to display course details using ViewData
        ViewData["Courses"] = _repository.GetCourses(id);

        // get course events
        var result = (from c in db.Courses
                      join ce in db.CourseEvents
                      on c.CourseId equals ce.CourseFk
                      join ced in db.CourseEventDates
                      on ce.CourseEventId equals ced.CourseEventFk
                      group ce by new { ce.CourseEventId, c.CourseId, c.CourseCode, c.CourseName, ce.CourseEventPrice } into grp
                      select new CourseDetailsVM
                      {
                          CourseEventId = grp.Key.CourseEventId,
                          CourseId = grp.Key.CourseId,
                          CourseCode = grp.Key.CourseCode,
                          CourseEventDateTimeFrom = (from c2 in db.CourseEventDates where (c2.CourseEventFk.Equals(grp.Key.CourseEventId)) select c2.CourseEventDateTimeFrom).Min(),
                          CourseEventDateTimeTo = (from c2 in db.CourseEventDates where (c2.CourseEventFk.Equals(grp.Key.CourseEventId)) select c2.CourseEventDateTimeFrom).Max(),
                          CourseEventDurationInDays = (from c2 in db.CourseEventDates where (c2.CourseEventFk.Equals(grp.Key.CourseEventId)) select c2.CourseEventDateTimeFrom).Count() / 2,
                          CourseName = grp.Key.CourseName,
                          CourseEventPrice = grp.Key.CourseEventPrice,
                          CourseEventDateId = grp.Key.CourseEventId
                      }).OrderBy(c => c.CourseEventDateTimeFrom);

    return View("Details", result);
    }

由于LINQ的运行上编译，我可以编译该项目没有任何错误。但访问课程时/详细查看我得到以下错误：
无法投类型'System.Int32'输入'System.Object的。 LINQ到实体仅支持铸造EDM基元或枚举类型

在以下领域作出CourseDetailsVM的一个新的实例时出现的错误： CourseEventDateTimeFrom，CourseEventDateTimeTo，CourseEventDurationInDays

The error occurs when making an new instance of CourseDetailsVM on the following fields: CourseEventDateTimeFrom, CourseEventDateTimeTo, CourseEventDurationInDays

我试图填补使用硬编码值所提到的属性和它工作得很好。所以我知道，那里的错误发生，但我不知道为什么，以及如何解决它。

I tried fill the mentioned properties using hard coded values and it worked fine. So I know, where the error occurs, but I don't know why and how to solve it.

由于所要求的Yuliam钱德拉的CourseEventDate类的内容（由EF生成）：

As requested by Yuliam Chandra, the content of the CourseEventDate class (generated by EF):

public partial class CourseEventDate
{
    public int CourseEventDateId { get; set; }
    public Nullable<int> CourseEventFk { get; set; }
    public Nullable<System.DateTime> CourseEventDateTimeFrom { get; set; }
    public Nullable<System.DateTime> CourseEventDateTimeTo { get; set; }
    public virtual CourseEvent CourseEvent { get; set; }
}

我希望某人你们能帮助我。

I hope that sb of you guys can help me.

感谢您，

罗宁

推荐答案

比较时可能造成的误差 CourseEventFk （ INT？）和 CourseEventId （ INT ）使用等于，其中的参数接受的对象类型，它是一个CLR方法。 LINQ到实体不支持CLR的方法。

The error could be caused when comparing CourseEventFk (int?) and CourseEventId (int) using Equals where its parameter accepts object type which is a CLR method. LINQ to Entities doesn't support CLR method.

尝试使用 == 运营商，这多少有点L2S兼容，在下面的代码。

Try to use == operator, which somewhat compatible to L2S, on following code.

CourseEventDateTimeFrom = ..where (c2.CourseEventFk == grp.Key.CourseEventId)..
CourseEventDateTimeTo = ..where (c2.CourseEventFk == grp.Key.CourseEventId)..
CourseEventDurationInDays = ..where (c2.CourseEventFk == grp.Key.CourseEventId)..

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