如何使用Linq-to-SQL的本地集合？

Question

我读了这个问题 ，这是我遇到的问题。 不幸的是，标记的解决方案没有帮助。 我可能误解了LINQ的一些非常明显的东西。

我正在尝试对各种反向查找。 我需要找到学生注册的所有课程。

这是代码......

public static IQueryable GetCoursesByStudent(string sStudentId)
{
    Ld_Sql_ServerDataContext ld_SqlContext = new Ld_Sql_ServerDataContext();

    // course-lesson IDs
    var activityEnrollmentIds = from ce in ld_SqlContext.YT_STUDENT_COURSE_ENROLLMENT_STATUS
                                where ce.STUDENT_EMPLOYEE_ID_NR.ToLower() == sStudentId.ToLower()
                                select ce.TRAINING_ACTIVITY_ID;

    // lesson parent course IDs
    var parentIds = from c in ld_SqlContext.YT_TRAINING_COMPONENT_RLTNPs
                    where activityEnrollmentIds.Contains(c.TRAINING_ACTIVITY_ID)
                    select c.PARENT_TRAINING_ACTIVITY_ID;

    // filtered list of courses    
    var courses = from c in ld_SqlContext.YT_TRAINING_COMPONENTs
                    where c.TRAINING_ACTIVITY_TYPE_DC == "Course" && 
                        (activityEnrollmentIds.ToList().Contains(c.TRAINING_ACTIVITY_ID)
                            || parentIds.ToList().Contains(c.TRAINING_ACTIVITY_ID))
                    select c;

    return courses;
}

我将结果数据绑定到ASP：ListBox，并在DataBind（）上抛出以下错误...

System.NotSupportedException：不支持具有本地集合的查询。

谁知道发生了什么事？

Answer 1

你能试试吗？

我认为你应该在使用它之前将activityEnrollmentIds和parentIds转换为List。

    public static IQueryable GetCoursesByStudent(string sStudentId)
    {
        Ld_Sql_ServerDataContext ld_SqlContext = new Ld_Sql_ServerDataContext();

        // course-lesson IDs
        var activityEnrollmentIds = (from ce in ld_SqlContext.YT_STUDENT_COURSE_ENROLLMENT_STATUS
                                    where ce.STUDENT_EMPLOYEE_ID_NR.ToLower() == sStudentId.ToLower()
                                     select ce.TRAINING_ACTIVITY_ID).ToList();

        // lesson parent course IDs
        var parentIds = (from c in ld_SqlContext.YT_TRAINING_COMPONENT_RLTNPs
                        where activityEnrollmentIds.Contains(c.TRAINING_ACTIVITY_ID)
                         select c.PARENT_TRAINING_ACTIVITY_ID).ToList();

        // filtered list of courses    
        var courses = from c in ld_SqlContext.YT_TRAINING_COMPONENTs
                      where c.TRAINING_ACTIVITY_TYPE_DC == "Course" &&
                          (activityEnrollmentIds.Contains(c.TRAINING_ACTIVITY_ID)
                              || parentIds.Contains(c.TRAINING_ACTIVITY_ID))
                      select c;

        return courses;
    }

Answer 2

我认为你可以做两个linq连接，只用一个查询就像在SQL上一样。 所以前两个查询可以消失。