我无法弄清楚这一点。我想传入一个 GenreID 并获取相应类型的对象列表，即如果我传入 MyGenre.RockAndRoll，我想要一个 RockAndRoll 对象列表。
Public Enum MyGenre Alternative = 0 rockAndRoll = 1 country = 2 End Enum
Public Interface IGenre
Inherits IDisposable
Property title As String
Property artist As String
Property duration As Decimal
Property rating As Integer
Sub Listen()
End Interface
Public Class RockAndRoll
Implements IGenre
Public Property artist As String Implements IGenre.artist
Public Property duration As Decimal Implements IGenre.duration
Public Property rating As Integer Implements IGenre.rating
Public Property title As String Implements IGenre.title
Public Sub Listen() Implements IGenre.Listen
'...
End Sub
#Region "IDisposable Support"
'...
#End Region
End Class
Public Class Country
Implements IGenre
Public Property artist As String Implements IGenre.artist
Public Property duration As Decimal Implements IGenre.duration
Public Property rating As Integer Implements IGenre.rating
Public Property title As String Implements IGenre.title
Public Sub Listen() Implements IGenre.Listen
'...
End Sub
#Region "IDisposable Support"
'...
#End Region
End Class
Public Function GetAlternativeList() As IEnumerable(Of IGenre)
Return GetIGenreList(MyGenre.alternative)
End Function
Public Function GetrockAndRollList() As IEnumerable(Of IGenre)
Return GetIGenreList(MyGenre.alternative)
End Function
Public Function GetIGenreList(p_MyGenre As MyGenre) As IEnumerable(Of IGenre)
Using db As New OracleDataContext
Return (From s In db.SongList
Where s.Genre= MyGenre _
Select CType(Activator.CreateInstance(p_MyGenre.GetGenreType,
New With {.title = s.title, .artist = p1.artist, etc etc etc}), p_MyGenre.GetGenreTyp)).ToList
End Using
End Function
<Extension()> _
Private Function GetGenreType(p_formatID As MyGenre) As Type
Select Case p_formatID
Case MyGenre.rockAndRoll
Return GetType(RockAndRoll)
Case MyGenre.country
Return GetType(PlayawayView)
Case Else
Return Nothing
End Select
End Function
编辑
#为了清楚起见，我想添加一个额外的示例。第一个令人困惑。让我们从格式的角度来看。
我想返回一份产品列表（DVD、CD、蓝光等），每种格式都有自己的内部类（用于艺术品尺寸、处理、合法性等原因）。
Class CD -> Implments IProduct
Class DVD -> Implements IProduct
Class BLURAY -> Implements IProduct
i.e. dim MyList = (from p in MyProductTable select p).tolist
returns 4 records.
(0)
title: Motown Unmixed
artist: Various
duration: 36:25
format: CD
upc: 024543246157
(1)
title: Classical Bytes - Bach
artist: Various
duration: 54:32
format: CD
upc: 709387901743
(2)
title: Star Wars: Episode VI - Return of the Jedi
artist: null
duration: 136.00
format: DVD
upc: 883928446172
(3)
title: Perfect Stranger
artist: null
duration: 95.36
format: BLU
upc: 043215190627
我想要的是一个列表 IPRODUCT。这可以通过点击数据库 3 次（对于每种格式类型）来完成。并将结果附加到 IPRODUCT 列表中。
dim MyProductList as new List(of IProduct)
MyProductList.addrange((from p in MyProductTable where p.format = "CD" select new CD with {.title = p.title, etc etc etc}).tolist)
MyProductList.addrange((from p in MyProductTable where p.format = "DVD" select new DVD with {.title = p.title, etc etc etc}).tolist)
MyProductList.addrange((from p in MyProductTable where p.format = "BLU" select new BLURAY with {.title = p.title, etc etc etc}).tolist)
我想将上面的 3 个查询合并为一个查询。此查询将返回 CD、DVD 和 BLURAY 对象的列表。