get all the values in Sql table using foreach - asp.net

Question

I need to get all the Ids' from the table "StaffSectionInCharge", it has only two columns StaffId and SectionId, I have values of StaffId and StudentId.....the problem is I can't get the records directly to this table.....am using entity framework and the design of this table is
[EdmRelationshipNavigationPropertyAttribute("Model", "StaffSectionInCharge", "Section")]
public EntityCollection<Section> Sections
{
get
{
return ((IEntityWithRelationships)this).RelationshipManager.GetRelatedCollection<Section>("Model.StaffSectionInCharge", "Section");
}
set
{
if ((value != null))
{
((IEntityWithRelationships)this).RelationshipManager.InitializeRelatedCollection<Section>("Model.StaffSectionInCharge", "Section", value);
}
}
}
I can access this table through staff table like
Staff staff = buDataEntities.Staffs.First(s => s.StaffId == StaffId);
Section section = buDataEntities.Sections.First(s => s.SectionId == SectionId);
staff.Sections.Add(section);
buDataEntities.savechanges();
like this I can add the records to this StaffSectionInCharge table....
here I want to get all the StaffIds for the corresponding SectionId
I tried getting like
DataAccess.Staff staffs = new DataAccess.Staff();
foreach (int staff in staffs.Sections.Select(s=>s.SectionId))
{
}
but its not working, can anyone help me here

Answer 1

var staffIds = buDataEntities.Staffs
.Where(st => st.Sections.Any(se => se.SectionId == SectionId))
.Select(st => st.StaffId)
.ToList();
or
var staffIds = buDataEntities.Sections
.Where(se => se.SectionId == SectionId)
.SelectMany(se => se.Staffs.Select(st => st.StaffId))
.Distinct()
.ToList();
Both options should work. If SectionId is the primary key of Section you can smplify the second code to:
var staffIds = buDataEntities.Sections
.Where(se => se.SectionId == SectionId)
.Select(se => se.Staffs.Select(st => st.StaffId))
.SingleOrDefault();