UnitOfWork, an excuse for multiple repositories

I needed a way of attaching multiple repositories to a presenter. Given I already had an IRepository abstraction, coming up with an IUnitOfWork seemed the next logical step.

The UoW opens a connection upon being created and, since it's a unit of work, initiates a transaction. Because I wanted the client code to be able to commit multiple transactions using the same UoW instance, I'm initiating a new transaction every time I Commit or Rollback.

So here it is:


IUnitOfWork class module

Option Explicit

Public Sub AddRepository(repo As IRepository)
End Sub

Public Property Get Repository(ByVal key As String) As IRepository
End Property

Public Sub Commit()
End Sub

Public Sub Rollback()
End Sub

UnitOfWork class module

```
Option Explicit

Private Const CONNECTION_STRING As String = "DRIVER={MySQL ODBC 5.1 Driver};UID=;PWD=;SERVER=;DATABASE=;PORT=;"

Private repositories As New Dictionary
Private adoConnection As New ADODB.Connection
Private cmd As New SqlCommand

Implements IUnitOfWork

Private Sub Class_Initialize()
adoConnection.ConnectionString = CONNECTION_STRING
adoConnection.Open
adoConnection.BeginTrans
End Sub

Private Sub Class_Terminate()
On Error GoTo ErrHandler

Set repositories = Nothing
If Not adoConnection Is Nothing Then
If adoConnection.State = adStateOpen Then
adoConnection.RollbackTrans 'rollback any uncommitted changes
adoConnection.Close
End If
Set adoConnection = Nothing
End If

Exit Sub

ErrHandler:
Err.Raise Err.number, Err.source, Err.description, Err.HelpFile, Err.HelpContext
End Sub

Public Sub AddRepository(ByVal key As String, ByRef repo As IRepository)
repo.SetConnection adoConnection
repositories.Add key, repo
End Sub

Public Property Get Repository(ByVal key As String) As IRepository
Set Repository = repositories(key)
End Property

Public Sub Commit()
On Error GoTo ErrHandler

adoConnection.CommitTrans
ad

First, to address your question, cleaning up should be a simple fix. Unfortunately, ExcludedOrdersPresenter isn't shown. However, that's where the change needs to be made. It should be responsible for setting Me.UnitOfWork = Nothing when it terminates. Honestly though, I can't quite figure out why it isn't doing that implicitly already. Perhaps because of the reference to adodb?

I don't see a need for the error handler in UnitOfWork.Class_Terminate. All it does is re-raise the error exactly as it is. Unless you intend on adding information to the description or source, just remove it and let the error bubble up. The same can be said for Commit and Rollback.

Actually, I take that back. Now, I'm not 100% on this, but if Commit errors, should it try to Rollback? I'm not sure. Consider it.

I don't think there's much more to say. Except maybe that I find the readability to be top notch.

StackExchange Code Review Q#60820, answer score: 2