Confused Newbie,
I would consider using a Generic class, passing the Enum & object type as
type parameters
Something like:
Dim employeManager as New Manager(Of Employee, Employee.MyFields)
The "trick" is the implementation of ItemFill, as you need the constructor
to Employee, generally I make Manager a base class...
Alternatively you could define "Manager" as a shared member of Employee
itself:
Public Class Employee
Public Shared ReadOnly Manager As New EmployeeManager()
Public Enum MyFields
NameSystemID = 0
NameFirst
NameMiddle
NameLast
DateHired
RecStatus
RecDateAdd
RecDateRev
RecAddBy
RecRevBy
End Enum
End Class
Public Class EmployeeManager
Inherits Manager(Of Employee, Employee.MyFields)
End Class
Where Manager is defined something like:
Public MustInherit Class Manager(Of T As Class, F)
Private _FieldList As ArrayList = Nothing
Public ReadOnly Property FieldList() As ArrayList
Get
If _FieldList Is Nothing Then
_FieldList = New ArrayList
Dim arNames() As String
arNames = [Enum].GetNames(GetType(F))
For x As Integer = 0 To arNames.GetUpperBound(0)
_FieldList.Add(New
VisarEnumBindingItem(EnumValue:=x, EnumLabel:=arNames(x)))
Next
End If
Return _FieldList
End Get
End Property
Private _FieldListString As String = ""
Public ReadOnly Property FieldListString() As String
Get
If _FieldListString = "" Then
Dim ThisItem As VisarEnumBindingItem = Nothing
For x As Integer = 0 To FieldList.Count - 1
ThisItem = CType(_FieldList(x),
VisarEnumBindingItem)
_FieldListString += ThisItem.StringValue & ", "
Next
_FieldListString = Left(_FieldListString,
_FieldListString.LastIndexOf(", "))
End If
Return _FieldListString
End Get
End Property
Public MustOverride Function ItemFill(ByVal ItemReader As
OleDbDataReader) As T
End Class
--
Hope this helps
Jay B. Harlow [MVP - Outlook]
..NET Application Architect, Enthusiast, & Evangelist
T.S. Bradley -
http://www.tsbradley.net
"Confused Newbie" <nope@spam.duhwrote in message
news:uUz5IF2qGHA.3648@TK2MSFTNGP03.phx.gbl...
| I'm converting an app written in VB 2003 to 2005 and need advice for how
to
| deal with this situation:
|
| The app has a number of "manager" classes that handle the data access.
They
| all have several routines that are identical, except for the object type
and
| database action specific to that particular class, such as "Public
ReadOnly
| Property Item(ByVal SystemID As Integer) As CEmployee" or "Public Shared
| Function Save(ByVal TheItem As CEmployee) As Boolean". Each of the object
| classes also have a bunch of common properties and methods that are
| inherited from an abstract base class.
|
| What I want to do with the manager classes is rewrite them using an
abstract
| class with MustOverride properties and methods. Where I'm hung up is the
| existing implementation uses an Enum that defines the database field names
| and ordinal positions in the SELECT statement used to create the
datareader.
| For example:
|
| Public Class EmployeeManager
|
| Public Enum MyFields
| NameSystemID = 0
| NameFirst
| NameMiddle
| NameLast
| DateHired
| RecStatus
| RecDateAdd
| RecDateRev
| RecAddBy
| RecRevBy
| End Enum
|
| Private Shared _FieldList As ArrayList = Nothing
| Public Shared ReadOnly Property FieldList() As ArrayList
| Get
| If _FieldList Is Nothing Then
| _FieldList = New ArrayList
| Dim arNames() As String
| arNames = MyFields.GetNames(GetType(MyFields))
| For x As Integer = 0 To arNames.GetUpperBound(0)
| _FieldList.Add(New VisarEnumBindingItem(EnumValue:=x,
| EnumLabel:=arNames(x))
| Next
| End If
| Return _FieldList
| End Get
| End Property
|
| Private Shared _FieldListString As String = ""
| Public Shared ReadOnly Property FieldListString() As String
| Get
| If _FieldListString = "" Then
| Dim ThisItem As VisarEnumBindingItem = Nothing
| For x As Integer = 0 To FieldList.Count -1
| ThisItem = CType(_FieldList(x), VisarEnumBindingItem)
| _FieldListString += ThisItem.StringValue & ", "
| Next
| _FieldListString = Left(_FieldListString,
| _FieldListString.LastIndexOf(", "))
| End If
| Return _FieldListString
| End Get
| End Property
|
| ' Overloaded Item property creates a command to retrieve by PK or AK,
| passes command to ItemFetch, which in turn calls ItemFill to unpack the
| datareader into the instance object and pass it back up the chain.
|
| Private Shared Function ItemFill(ByVal ItemReader As OleDbDataReader) As
| CEmployee
| With ItemReader
| Return New CEmployee(RecSystemID:=.GetInt32(MyFields.NameSyst emID),
| RecStatus:=VisarGoodies.MakeInt32(.GetValue(MyFiel ds.RecStatus)),
| RecDateAdd:=VisarGoodies.MakeDate(.GetValue(MyFiel ds.RecDateAdd)),
| RecDateRev:=VisarGoodies.MakeDate(.GetValue(MyFiel ds.RecDateRev)),
| RecAddBy:=VisarGoodies.MakeInt32(.GetValue(MyField s.RecAddBy)),
| RecRevBy:=VisarGoodies.MakeInt32(.GetValue(MyField s.RecRevBy)),
| NameFirst:=VisarGoodies.MakeString(.GetValue(MyFie lds.NameFirst)),
| NameMiddle:=VisarGoodies.MakeString(.GetValue(MyFi elds.NameMiddle)),
| NameLast:=VisarGoodies.MakeString(.GetValue(MyFiel ds.NameLast)))
| End With
| End Function
|
| End Class
|
| The way it's designed, changes to the order of fields in the select
| statement or even actual field names only need to be made in the Enum.
The
| select, insert, and update statements are dynamically constructed in each
of
| the managers from the FieldList arraylist.
|
| How can I create the identical functionality using an abstract class in
| VB2005, also placing the code that constructs the "FieldList" from the
Enum
| into a shared method in a separate utility class? I tried using a
| placeholder enum and the FieldList property in the base class, and a
| shadowed enum in a derived class, but when executed, it uses the base
enum,
| not the shadowed one. It does work when place the enum and override
| FieldList in each of the derived classes but I don't want to implement
| identical code over and over.
|
| Thanks,
|
| Gino
|
|
