VB.NET How To Prevent Infinite Recursion During Object Population - vb.net

Question

I'm a bit stuck right now in trying to determine the best solution to prevent an infinite recursion loop. Perhaps it's not exactly "recursion", but it's a set of function calls that I can pretty much guarantee will be calling each other indefinitely if I can't come up with a solution.
In trying to figure out how to explain the issue, it seems the best way I can come up with is to start with some simplified (and redacted) code. For this example, I'll use a Classroom and a Student.
Public Class Classroom
Public Property ClassroomID As Integer
Public Property ClassroomDescription As String
Public Property Students As List(Of Student)
Public Sub New(ByVal ClassroomID As Integer)
Initialize()
GetClassroomDetail(ClassroomID)
End Sub
Public Sub GetClassroomDetail(ByVal ClassroomID As Integer)
Dim Reader As SqlDataReader
' HERE'S WHERE I MAKE THE DATABASE CALL TO
' GET THE CLASSROOM RECORD DETAILS
FillClassroomRecord(Reader)
End Sub
Private Sub FillClassroomRecord(Reader)
While Reader.Read
ClassroomID = CType(Reader("ClassroomID"), Integer)
ClassroomDescription = CType(Reader("ClassroomDescription"), String)
Students = GetClassroomStudents(ClassroomID)
End While
End Sub
Private Function GetClassroomStudents(ByVal ClassroomID As Integer) As List(Of Student)
Dim StudentData As DataTable
Dim ClassroomStudents As New List(Of Student)
' I PULL A LIST OF STUDENTS RELATED TO THE SPECIFIC CLASSROOMID
For Each StudentRow As DataRow In StudentData.Rows
Dim NewStudent As New Student(CType(StudentRow("studentid"), Integer))
ClassroomStudents.Add(NewStudent)
Next StudentRow
Return ClassroomStudents
End Function
End Class
So far, pretty straight forward. However, the problem comes in the fact that the same student may be tied to multiple classrooms. I want to have a similar method in the Student object to be able to pull all related classrooms for that student.
Public Class Student
Public Property StudentID As Integer
Public Property Name As String
Public Property Classrooms As List(Of Classroom)
...
Private Function GetStudentClassrooms(ByVal StudentID As Integer) As List(Of Classroom)
Dim ClassroomData As DataTable
Dim StudentClassrooms As New List(Of Classroom)
' PULL A LIST OF CLASSROOMS RELATED TO THE SPECIFIC STUDENTID
For Each ClassroomRow As DataRow In ClassroomData.Rows
Dim NewClassroom As New Classroom(CType(ClassroomRow("classroomid"), Integer))
StudentClassrooms.Add(NewClassroom)
Next ClassroomRow
Return StudentClassrooms
End Function
End Class
So, my consternation at this point is, how do I prevent it from constantly looping back and forth between the classrooms and the students populating the same things over and over again in an infinite loop?
The only thing I can think to do is to set a Boolean variable somewhere that I can set to identify whether or not to keep drilling down. The problem is that my brain is a bit fried at the moment, and I can't figure out how to implement such a solution.
Some of the searching I've done also mentioned the possibility of some sort of "backtracking", which sounds cool, but doesn't seem very likely to work in this type of situation. Of course, I could be wrong on that, and I'd love to see any sort of implementation that is somehow capable of intelligently identifying if I'm just looping the same things over and over again.
What I'd like to see happen is the top-level Classroom object creation should pick up its Student objects, which should pick up any additional Classroom objects to which they are associated, including each of those Classroom object's Student objects, and then it stops.
I hope that all makes sense. It's actually even more complicated than this as there are other similar objects that will be tied back to the top-level object (Classroom), which should also follow the same basic rules - don't dig too deep into the "sub" records, and prevent an infinite recursive loop
If any clarification is necessary, please let me know. I truly appreciate any assistance you can provide.

Answer 1

I think I may have an idea of how to solve this, but I'd like to get some feedback on my idea.
If I create an overload of the New constructor that accepts a boolean value (GetRelatedDetails), then I can call it initially with that flag set to True. Just about everything else should remain the same, other than passing this value down the chain. Using the above example, it would look something like this:
Public Class Classroom
Public Property ClassroomID As Integer
Public Property ClassroomDescription As String
Public Property Students As List(Of Student)
Public Sub New(ByVal ClassroomID As Integer)
Initialize()
GetClassroomDetail(ClassroomID, False)
End Sub
' OVERLOAD WITH BOOLEAN VALUE TO GET RELATED DETAILS
Public Sub New(ByVal ClassroomID As Integer, ByVal GetRelatedDetails As Boolean)
Initialize()
GetClassroomDetail(ClassroomID, GetRelatedDetails)
End Sub
Public Sub GetClassroomDetail(ByVal ClassroomID As Integer, ByVal GetRelatedDetails As Boolean)
Dim Reader As SqlDataReader
' HERE'S WHERE I MAKE THE CALL TO GET THE
' CLASSROOM RECORD DETAILS FROM THE DATABASE
FillClassroomRecord(Reader, GetRelatedDetails)
End Sub
Private Sub FillClassroomRecord(ByVal Reader As SqlDataReader, ByVal GetRelatedDetails As Boolean)
While Reader.Read
ClassroomID = CType(Reader("ClassroomID"), Integer)
ClassroomDescription = CType(Reader("ClassroomDescription"), String)
If GetRelatedDetails Then
Students = GetClassroomStudents(ClassroomID)
End If
End While
End Sub
Private Function GetClassroomStudents(ByVal ClassroomID As Integer) As List(Of Student)
Dim StudentData As DataTable
Dim ClassroomStudents As New List(Of Student)
' I PULL A LIST OF STUDENTS RELATED TO THE SPECIFIC CLASSROOMID
For Each StudentRow As DataRow In StudentData.Rows
Dim NewStudent As New Student(CType(StudentRow("studentid"), Integer))
ClassroomStudents.Add(NewStudent)
Next StudentRow
Return ClassroomStudents
End Function
End Class
Then the Student object does basically the same thing:
Public Class Student
Public Property StudentID As Integer
Public Property StudentName As String
Public Property Classrooms As List(Of Classroom)
Public Sub New(ByVal StudentID As Integer)
Initialize()
GetStudentDetail(StudentID, False)
End Sub
' OVERLOAD WITH BOOLEAN VALUE TO GET RELATED DETAILS
Public Sub New(ByVal StudentID As Integer, ByVal GetRelatedDetails As Boolean)
Initialize()
GetStudentDetail(StudentID, GetRelatedDetails)
End Sub
Public Sub GetStudentDetail(ByVal StudentID As Integer, ByVal GetRelatedDetails As Boolean)
Dim Reader As SqlDataReader
' HERE'S WHERE I MAKE THE CALL TO GET THE
' STUDENT RECORD DETAILS FROM THE DATABASE
FillStudentRecord(Reader, GetRelatedDetails)
End Sub
Private Sub FillStudentRecord(ByVal Reader As SqlDataReader, ByVal GetRelatedDetails As Boolean)
While Reader.Read
StudentID = CType(Reader("StudentID"), Integer)
StudentName = CType(Reader("StudentName"), String)
If GetRelatedDetails Then
Classrooms = GetStudentClassrooms(StudentID)
End If
End While
End Sub
Private Function GetStudentClassrooms(ByVal StudentID As Integer) As List(Of Classroom)
Dim ClassroomData As DataTable
Dim StudentClassrooms As New List(Of Classroom)
' PULL A LIST OF CLASSROOMS RELATED TO THE SPECIFIC STUDENTID
For Each ClassroomRow As DataRow In ClassroomData.Rows
Dim NewClassroom As New Classroom(CType(ClassroomRow("classroomid"), Integer))
StudentClassrooms.Add(NewClassroom)
Next ClassroomRow
Return StudentClassrooms
End Function
End Class
You'll notice that, even if I pass in a value of True to the initial object, when it gets to the Fill method, and steps into the GetClassroomStudents or GetStudentClassrooms, it just calls the New constructor overload that defaults to False. This way, I'm guessing that it should prevent it from looping infinitely back through the same records over and over again.
Of course, I'm open to any other suggestions or ideas on the best way to implement this, but I think this is what I'm going to try to do for now.