Entity Framework Child & Parent (List Property) - sql-server

Question

I'm working on a project with EF5, Vb.net, AJAX (Javascript), ASMX-Webservices and HTML.
My question is if i have (example classes):
Public Class Company
Public Property CompanyId As Integer
Public Property Name As String
Public Overridable Property Companytype As Companytype
End Class
and the Class:
Public Class Companytype
Public Property CompanytypeId As Integer
Public Property Name As String
-> Public Overridable Property Companies As List(Of Company)
End Class
do I need the -> marked line?
I'm afraid but I really don't know which advance this line brings to me.
Actually I can read all the Companies of a Companytype like this:
Public Shared Function PostCompanyTypeCompanies() As List(Of Company)
Dim db As New Context
Dim x As Integer = 1
Dim y = (From c In db.Companies Where c.CompanyType.CompanyTypeId = x Select New With _
{c.Name, _
c.CompanyType})
Dim z As List(Of Company) = y.AsEnumerable() _
.Select(Function(t) New Company With _
{.Name = t.Name, _
.CompanyType = t.CompanyType}).ToList()
Return z
End Function
This with 'x' is just an example, I can just pass the CompanytypeId to the function.
The problem with the lists is, I always get a circular reference when I want to get the Companytypes for a new Company and I can't access the companytype of a Company like:
Company.Companytype.Name
When I do it without the list everything works fine, because i can store the whole Companytpe to the Company.
I tried the other possibility with setting the Getter of the Child & Parent Properties to Protected then the problem was logically also that I couldn't access the variable as I described a 3 lines above.
So the important question is: Is this -> List Property mandatory?
Thanks for you help.

Answer 1

do I need the -> marked line? NO. It is redundant information (with no real use), which potentially, might provoke consistency errors. Example:
Dim company1 As New Company()
Dim listCompanies As New List(Of Company)()
Dim companiesType1 As New Companytype()
listCompanies.Add(company1)
With companiesType1
.CompanytypeId = 1
.Name = "Type 1"
.Companies = listCompanies
End With
With company1
.CompanyId = 1
.Name = "1"
.Companytype = companiesType1
End With
The code above defines Company1 and the associated type (companiesType1... although we have the problem of "first the egg or the chicken", what gives a first idea of why the chosen approach is erroneous). If you create a new company of the same type:
Dim company2 As New Company()
With company2
.CompanyId = 2
.Name = "2"
.Companytype = companiesType1
End With
You would have to redefine companiesType1 (update its Companies property), to keep the consistency. But, as far as this is redundant information, Companytype would "do the job" independently upon this fact:
If (company2.Companytype Is company1.Companytype) Then
'Both companies have the same type
End If
The aforementioned condition will always be true: either if companiesType1 contains the right information (was updated with company2) or not.
If you need to have a list of all the companies belonging to certain type, you should better rely on a different class storing all the values (e.g., allTheCompanies).