当使用静态类时，方法x不支持转换为SQL

Question

我在视图中使用MVC平台和jqGrid。下面是控制器代码的一部分，将json返回到网格

IQueryable<CalendarViewModel> callendars =
            from call in (new KYTCDataContext()).Calendars
            where call.AcademicYear == id
            select Matcher.Calendar(call);
        if (jqGridParameters._search != false)
        {
            callendars = callendars.Where(jqGridParameters.WhereClause);
        }
        if (jqGridParameters.sidx != null)
            callendars = callendars.OrderBy(
                jqGridParameters.sidx.Substring(8) + " " + jqGridParameters.sord.ToLower());
        var count = callendars.Count();
        int pageIndex = jqGridParameters.page;

匹配器是静态类。下面是类

使用的方法

public static class Matcher
    { 
public static CalendarViewModel Calendar(Calendar call)
        {
            return new CalendarViewModel
            {
                ID = call.ID,
                Name = call.Name,
                StartDate = call.StartDate,
                EndDate = call.EndDate,
                AcademicYear = call.AcademicYear
            };
        }
}

在

行

var count = callendars.Count();

我收到这个错误:

方法'KYTC.Models.CalendarViewModel Calendar(KYTC.Data.Calendar)'不支持转换为SQL。

，但当我改变LINQ查询如下:

IQueryable<CalendarViewModel> callendars =
            from call in (new KYTCDataContext()).Calendars
            where call.AcademicYear == id
            select new CalendarViewModel
            {
                ID = call.ID,
                Name = call.Name,
                StartDate = call.StartDate,
                EndDate = call.EndDate,
                AcademicYear = call.AcademicYear
            };

我的代码运行良好。

我的类定义有什么问题?

Answer 1

您的类定义没有问题。问题是，您根本无法在Linq-to-SQL(或EntityFramework)查询中调用任意函数。只有少数预定义的方法可以转换为SQL语法。最后一个方法是从查询中返回CalendarViewModel对象的正确方法。

但是，你也可以这样做:

public static Expression<Func<Calendar, CalendarViewModel>> CalendarExpression()
{
    return c => new CalendarViewModel
    {
        ID = c.ID,
        Name = c.Name,
        StartDate = c.StartDate,
        EndDate = c.EndDate,
        AcademicYear = c.AcademicYear
    };
}
var calendarExpr = Match.CalendarExpression();
IQueryable<CalendarViewModel> callendars =
    (from call in (new KYTCDataContext()).Calendars
     where call.AcademicYear == id
     select call)
    .Select(calendarExpr);