simplify linq to sql returning multiple object

Question

ok, i have to admit that until now i still do not know the best way to return multiple objects using linq to sql.

 public IList<Course> GetAllStudentCourses()
    {
        IList<Course> output = new List<Course>();
        using (lenDataContext db = new lenDataContext())
        {
            var result =
                 from ct in db.CourseByTutors
                 join c in db.Courses on ct.CourseId equals c.Id
                 join u in db.Users on ct.TutorId equals u.Id
                 select new
                 {
                     c,
                     u,
                 };
            foreach (var r in result)
            {
                Course course = new Course();
                course.CourseByTutor = new CourseByTutor();
                course = r.c;
                course.IsGroupString = (r.c.IsGroup == 1) ? "Yes" : "No";
                course.User = r.u;

                output.Add(course);
            }
        }
        return output;
    }

I would like to return Course and User objects back to UI.

 private void InitializeData()
    {
        Course c = new Course();
        dgCourses.AutoGenerateColumns = false;

        bs.DataSource = c.GetAllStudentCourses().ToList();          

        dgCourses.DataSource = bs; //bs is bindingsource
    }

How do i display the user data e.g. Name to the Gridview? i have put User.Name to the datapropertyName but it still showing nothing. my Course.User has value.

Yes how do i display some user property back to my GV(Gridview) since i return the object as <Course> — VeecoTech
– VeecoTech, Commented Mar 20, 2011 at 1:32
Do you not have relationships defined in your schema between CourseByTutors -> Course and CourseByTutors -> User? Is that why you're joining them in your query? — hunter
– hunter, Commented Mar 20, 2011 at 1:35
yes, i do not have relationships defined. I tried this in my UI, Course c = new Course(); GVCourse.datasource = c.GetAllStudentCourses().ToList(); Then i set the Gridview dataPropertyName to c.User.Name and Course.User.Name but both also did not show me the name — VeecoTech
– VeecoTech, Commented Mar 20, 2011 at 1:48
@Joel Gauvreau: i have even tried to put only the User.Name to the dataproteprtyName but it din show me anything. — VeecoTech
– VeecoTech, Commented Mar 20, 2011 at 1:56

score 1 · Accepted Answer · 2011-03-20 01:56:41Z

1

If you return db.CourseByTutors you should have access to both the users and the courses. The two inner joins you are doing above seem unessecary because you should be able to access them via EntitySet. Just use the navigation properties to access all the users and courses.

public IQueryable<CourseByTutors> GetAllStudentCourses()
{
    lenDataContext db = new lenDataContext();
    return db.CourseByTutors;
}

Then in your gridview you can reference the properties by Coures.property and Users.property on a databound column. You can't use a using statement though because as soon as you return the IQueryable you would dispose of the datacontext.

edited Mar 20, 2011 at 1:56

answered Mar 20, 2011 at 1:29

user342706

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Joel Gauvreau · Accepted Answer · 2011-03-20 02:29:45Z

0

You can flatten your object by wrapping them in another object :

public class CourseDisplay
{
   private Course course; 

   public CourseDisplay(Course course)
   {
       this.course = course;
   }

   public string CourseName 
   { 
       get { return course.Name; } 
   }

   public string UserName 
   { 
       get { return course.User.Name;} 
   }
}

It is simpler to bind to a child property in ObjectListView.

edited Mar 20, 2011 at 2:29

answered Mar 20, 2011 at 1:27

Joel Gauvreau

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1 Comment

VeecoTech Over a year ago

ya, but i tried not to add extra property as it will bring more confusion

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