Class Association in VB.Net

[Dani]

Hi all,
I'm programming an application with OOP. I've got a one to many
relationship between 2 tables, and I read this can be implemented thru
class association.

I've got 2 tables: Customers and Budgets. One Cutomer may have
multiple Budgets.

In the VS Class Diagram, I tried to create the association but I need
to define the property Budget in class Customer, as a list, otherwise
it wouldn't let me do it.

Any ideas about this?

Thanks a lot in advance.

Daniela

[Cerebrus]

That's perfectly fine. Each Customer has a List of Budgets exposed
through a property of the Customer class.

[Stephen Russell]

-----------------------------------------

Think of a container, Customer, that holds other containers like
List<Budget> and List<Orders>.

--
Stephen Russell

901.246-0159 cell

[Daniela Zurita]

Thank you for your answers, Stephen and Cerebrus!

But now, could you please give me an example of definition and how to implement the classes? 

I've got an example and there are points i don'get. here my questions.

Side 1

Class Customer 

Friend Sub SetBudget(ByVal budget As Budget)

_budget = budget

End Sub

 

Public Property Budget() As Budget

Get

  Return _budget

End Get

Set(ByVal Value As Budget)

If Not _budget Is Nothing Then

_budget.Customers_with_budget.Delete(Me)

End If

_distribuidora = Value

If Not _budget Is Nothing Then

_budget. .Customers_with_budget.Append(Me)

End If

End Set

End Property

'what about add and delete methods? when I delete a customer shoud I delete a budget? Don't know how to do this

Side * 

'here I create a collection of customers with budget

Public Class Customers_with_budget

Implements IEnumerable

Private _budget As Budget

Private _htCustomers_with_budget As Hashtable

Friend Sub New(ByVal  budget As Budget )

_budget = budget

_htCustomers_with_budget = New Hashtable

End Sub

…

End Class

Public Sub Add(ByVal customer As Customer)

If Not _ht Customers_with_budget.Contains(customer) Then

_htCustomers_with_budget.Add(customer.Name, ... ,Customer) 'here I add other properties of a customer like address, contact number, etc

customer.setBudget(_budget)

Else

Throw New System.Exception("Already existing Customer")

End If

End Sub

Friend Sub Append(ByVal customer As Customer)

_htCustomers_with_budget.Add(customer.Name, ..., customer)

End Sub

Public Sub Remove(ByVal customer As Customer)

customer.SetBudget(Nothing) 'remove opposite reference

Me.Delete(customer)  'delete customer from collection

End Sub

Public Sub Remove(ByVal name As String)

'Delete opposite reference

Item(name).SetBudget(Nothing)

Me.Delete(Item(name)) ‘remove from collection

End Sub

Friend Sub Delete(ByVal customer As Customer)

_htCustomers_with_budget.Remove(customer.Name) 'what about other elements in customer class like address and contact number?

End Sub

'Clear method is called from Dispose method in Budget class and deletes elements of collection class 

Public Sub Clear()

Dim en As IDictionaryEnumerator

Dim name As String

en = _htCustomers_with_budget.GetEnumerator

While en.MoveNext()

name = CType(en.Key, String) 'i don't get this Ctype function

Me.Remove(name)

End While

_htCustomers_with_budget.Clear()

End Sub

and next question is how do I implement the collection class with table Budget? 

thanks a million!

Dani 

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[Cerebrus]

Hi Daniela,

I have posted an example that illustrates how to create the classes
and some sample usage at:

http://pastebin.com/cDmwxZL9

I have tried to explain via comments where possible, but feel free to
ask if you have any doubts. I hope you are familiar with VB 9.0
syntax. A couple of questions in your post remain unanswered and I try
to address them below:

1. What about Add/Delete? when I delete a customer shoud I delete a
budget? Don't know how to do this.

Add, Delete are implemented in my example. When you delete a Customer
instance, associated budget instances are automatically deleted.

2. What about other elements in customer class like address and
contact number?
Those elements get added/deleted/modified when the Customer instance
is added/deleted/modified.

You need to implement custom collection classes only if you are using
a version of .NET prior to 2.0 (pre-VS 2005) or the existing
collection classes do not suffice for your requirement. In this case,
I believe that the existing generic collections do suffice.

Another point is that I have loaded data into the instances manually.
In a real-world scenario, you would load the data from database
tables. Ideally, the customer's budgets would be loaded when a
customer is created (for instance, by initiating a database call
within the Customer class constructor).

On Jan 11, 5:57 pm, Daniela Zurita <danielaazur...@gmail.com> wrote:
> Thank you for your answers, Stephen and Cerebrus!
> But now, could you please give me an example of definition and how to
> implement the classes?
> I've got an example and there are points i don'get. here my questions.
>
>

> thanks a million!
> Dani
>

[Cerebrus]

This is another example that was intended to showcase Generic methods,
but also illustrates the class association concept:

http://pastebin.com/w7e1Jn6J

[Daniela Zurita]

Cerebrus, thank you very much for this information, really apreciate it. I'll implement my class association according to your examples and see how I go.

kind regards,

Daniela

[Cerebrus]

Good luck !

Let us know if you face any hurdles. :-)