I needed a way of [attaching multiple repositories to a presenter](http://codereview.stackexchange.com/q/60595/23788). Given I already had an `IRepository` abstraction, coming up with an `IUnitOfWork` seemed the next logical step.

The code works, but I'm having issues with transactions because of MySQL (not sure if it's the [driver](http://stackoverflow.com/a/23117572/1188513) or the [underlying db engine](http://stackoverflow.com/a/20918337/1188513), but everything just goes through as if there was no transaction involved) - but that's irrelevant to the actual code - I'm sure I can hook this up to a SQL Server backend and it will work just as expected.

The UoW opens a connection upon being created, and initiates a transaction too. 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.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
        adoConnection.BeginTrans
        
        Exit Sub
        
    ErrHandler:
        Err.Raise Err.number, Err.source, Err.description, Err.HelpFile, Err.HelpContext
    End Sub
    
    Public Sub Rollback()
        On Error GoTo ErrHandler
        
        adoConnection.RollbackTrans
        adoConnection.BeginTrans
        
        Exit Sub
        
    ErrHandler:
        Err.Raise Err.number, Err.source, Err.description, Err.HelpFile, Err.HelpContext
    End Sub
    
    Private Sub IUnitOfWork_AddRepository(ByVal key As String, ByRef repo As IRepository)
        AddRepository key, repo
    End Sub
    
    Private Sub IUnitOfWork_Commit()
        Commit
    End Sub
    
    Private Property Get IUnitOfWork_Repository(ByVal key As String) As IRepository
        Set IUnitOfWork_Repository = Repository(key)
    End Property
    
    Private Sub IUnitOfWork_Rollback()
        Rollback
    End Sub

---

Here's how this code helped solve the [*presenter-that-isn't-a-presenter* problem](http://codereview.stackexchange.com/q/60595/23788) - I simply add the two repositories I need, and the presenter can call methods on both `UnitOfWork.Repository("ExcludedOrders")` and `UnitOfWork.Repository("Orders")`, so I could get rid of the `OrderHeaderPresenter` empty shell:

    Public Sub MaintainExcludedOrders()
        
        On Error GoTo ErrHandler
        If IsBusy Then Exit Sub
    
        Dim orders As New OrderHeaderRepository
        Dim exclOrders As New ExcludedOrdersRepository
        
        Dim uow As New UnitOfWork
        uow.AddRepository "ExcludedOrders", exclOrders
        uow.AddRepository "Orders", orders
        
        Dim presenter As New ExcludedOrdersPresenter
        Set presenter.UnitOfWork = uow
        
        SetupSimplePresenter presenter, _
                             GetResourceString("ExcludedOrdersTitle"), _
                             GetResourceString("ExcludedOrdersInstructionsText"), _
                             CRUD
        
        presenter.Show
    
    CleanExit:
        Set uow = Nothing
        Set presenter = Nothing
        Exit Sub
        
    ErrHandler:
        MsgBox Err.description, vbCritical, GENERIC_ERR_MSG
        Resume CleanExit
    End Sub