Question

I have 3 tables:

Degree(Id int(PK), DegreeName string)

1   Bachelor
2   Master
3   PhD

Track(Id int(PK), DegreeId int(FK), TrackName string)

1   2   Engineer
2   1   Technician
3   1   Assistant
4   2   Physicist
5   3   Doctor

Group(Id int(PK), TrackId int(FK), GroupName string)

1   4   Group1
2   3   Group2
3   1   Group3
4   3   Group4
5   2   Group5

there is a one to many relation between Degree and Track, and another one to many relation between Track and Group.

I have this class:

Public class DegreeDetails
{
    public List<Track> TrackList { get; set; }
    public List<Group> GroupsList { get; set; }
}

to get all tracks these belong to bachelor degree, which are technician and assistant, I use this code:

In the controller I use this code:

DegreeDetails MyView = new DegreeDetails();
MyView.TrackList = entity.Track.Where(s => s.DegreeID == 1).ToList();

how to get a Group List of all groups these study tracks belong to bachelor degree, which should be Group2, Group4 and Group5.

Answer 1

Probably the best thing to do is to join these tables. You could create a view in your database, or you can join tables using Linq.

This should work:

MyView.GroupList = (from d in entity.Degree
                    join t in entity.Track on d.Id equals t.DegreeId
                    join g in entity.Group on t.Id equals g.TrackId
                    where d.Id == 1
                    select g).Distinct().ToList();

UPDATE If you want to use lambda exp, try this:

MyView.GroupList = entity.Degree.Where(d => d.Id == 1)
                    .Join(entity.Track, d => d.Id, t=> t.DegreeId, (d, t) => t)
                    .Join(entity.Group, t => t.Id, g => g.TrackId, (t, g) => g)
                    .Distinct().ToList();