ここには、ジェネリックを使用する非常に基本的な例があります。方法GetPropFromDatabase
はSelect Case
を使用していますが、実際のデータベース検索呼び出しを行うことは明らかです。あなたのオブジェクトのセットアップ方法に応じてGetProperties()
にBindingFlags
でプレイする必要がある場合があります
Option Explicit On
Option Strict On
Public Class Form1
Private Sub Form1_Load(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles MyBase.Load
Dim X = CreateObject(Of TestClass)()
Trace.WriteLine(X.PropertyA)
Trace.WriteLine(X.PropertyB)
Me.Close()
End Sub
''//Of T as New means that the object must have a constructor
Private Function CreateObject(Of T As New)() As T
''//Create our object
Dim O As New T
''//Get the type properties
Dim Props = GetType(T).GetProperties()
''//Loop through each property
For Each P In Props
''//Set the value of our return type by property name
P.SetValue(O, GetPropFromDatabase(P.Name), Nothing)
Next
''//Return our object
Return O
End Function
''//This function would obviously do a lot more
Private Shared Function GetPropFromDatabase(ByVal name As String) As String
Select Case name
Case "PropertyA"
Return "Value1"
Case "PropertyB"
Return "Value2"
End Select
Throw New ApplicationException(String.Format("Unknown database column : {0}", name))
End Function
End Class
Public Class TestClass
Public Property PropertyA As String
Public Property PropertyB As String
End Class
EDIT
。
EDIT 2
ます。また、カスタム属性を使用してに見たいと思うかもしれません。例えば、データベースに[First Name]
という名前の列がある場合は、スペースのためにオブジェクトのプロパティとして存在できないことは明らかです。カスタム属性を使用すると、特定のプロパティを無視したり、特別な方法で解析したりすることができます。下のコードは、上記のコードの拡張バージョンを示しています。
Option Explicit On
Option Strict On
Public Class Form1
Private Sub Form1_Load(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles MyBase.Load
Dim X = CreateObject(Of TestClass)()
Trace.WriteLine(X.PropertyA)
Trace.WriteLine(X.PropertyB)
Trace.WriteLine(X.FirstName)
Me.Close()
End Sub
''//Of T as New means that the object must have a constructor
Private Function CreateObject(Of T As New)() As T
''//Create our object
Dim O As New T
''//Get the type properties
Dim Props = GetType(T).GetProperties()
''//Will hold the name of the database column to get the value of
Dim PropName As String
''//Will hold our collection of attributes on the property
Dim CustomAttributes() As Object
''//Loop through each property
For Each P In Props
''//Default the value to the property name
PropName = P.Name
''//Try to get any custom attributes for the property
CustomAttributes = P.GetCustomAttributes(True)
''//See if we have anything to work with
If (CustomAttributes IsNot Nothing) AndAlso (CustomAttributes.Count > 0) Then
''//Loop through each attribute
For Each A In CustomAttributes
''//If the attribute is our custom one defined below
If TypeOf A Is ColumnNameInDatabase Then
''//Use the manually set column name instead
PropName = DirectCast(A, ColumnNameInDatabase).ColumnNameInDatabase
''//No reason to loop through any more attributes so exit
Exit For
End If
Next
End If
''//Set the value of our return type by property name
P.SetValue(O, GetPropFromDatabase(PropName), Nothing)
Next
''//Return our object
Return O
End Function
''//This function would obviously do a lot more
Private Shared Function GetPropFromDatabase(ByVal name As String) As String
Select Case name
Case "PropertyA"
Return "Value1"
Case "PropertyB"
Return "Value2"
Case "First Name"
Return "Bob Dole"
End Select
Throw New ApplicationException(String.Format("Unknown database column : {0}", name))
End Function
End Class
Public Class TestClass
Public Property PropertyA As String
Public Property PropertyB As String
<ColumnNameInDatabase("First Name")> Public Property FirstName As String
End Class
Public Class ColumnNameInDatabase
Inherits Attribute
Private _ColumnNameInDatabase As String
Public ReadOnly Property ColumnNameInDatabase As String
Get
Return Me._ColumnNameInDatabase
End Get
End Property
Public Sub New(ByVal columnNameInDatabase As String)
Me._ColumnNameInDatabase = columnNameInDatabase
End Sub
End Class