How can I use a local collection with Linq-to-SQL?

Question

I read this question which is the same issue I'm having. Unfortunately, the marked solution didn't help. I'm probably misunderstanding something really obvious about LINQ.

I'm trying to do a reverse lookup of sorts. I need to find all courses that a student is enrolled in.

Here's the code...

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;
}

I'm databinding the results to a an ASP:ListBox and the following error gets thrown on DataBind()...

System.NotSupportedException: Queries with local collections are not supported.

Anybody know what's going on?

Answer 1

Can you try this ?

I think you should convert activityEnrollmentIds and parentIds into List before use it.

    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

I think you can do two linq joins and do the work with just one query as you would do on SQL. So the first two queries can go away.