無法投射「System.Collections.Generic.HashSet」類型的對象

Question

我想用EF Code-First將這些類添加到數據庫中。填充對象並嘗試填充上下文「dbContext.Tracks.Add（t1）」後。我收到錯誤「無法投射'System.Collections.Generic.HashSet`1 [Vinyl7]'類型的對象鍵入'Vinyl7'」任何人都可以指出我失蹤了什麼？

Public Class Vinyl7 

    <Key> 
    Public Overridable Property mediaId As Long 
    Public Overridable Property parentMediaId As System.Nullable(Of Long) 
    Public Overridable Property side As String 

    <ForeignKey("mediaId"), Required> 
    Public Overridable Property track As Track 

End Class 


Public Class Track 

    <Key> 
    Public Property mediaId As Long 
    Public Property title As String 

    Public Overridable Property Vinyl7T As ICollection(Of Vinyl7) = New HashSet(Of Vinyl7) 
End Class 

這是我的上下文

Public Class MediaRepo : Inherits DbContext 

    Public Sub New() 
     MyBase.New("name=MediaDB") 

    End Sub 

    Protected Overrides Sub OnModelCreating(modelBuilder As DbModelBuilder) 

    End Sub 

    Public Property Vinyl7s As DbSet(Of Vinyl7) 
    Public Property Tracks As DbSet(Of Track) 

End Class 

這是我的方法。

 Using db = New MediaRepo 
      Dim t1 = New Track 
      t1.title = "Kutchie" 
      Dim t2 = New Track 
      t2.title = "Drug Trade" 

      Dim a = New Media.Vinyl7 
      a.side = "A" 
      a.parentMediaId = t1.mediaId 
      a.track = t1 
      Dim b = New Media.Vinyl7 
      b.side = "B" 
      b.parentMediaId = t1.mediaId 
      b.track = t2 
      t1.Vinyl7T.Add(a) 
      t1.Vinyl7T.Add(b) 
      db.Tracks.Add(t1) 

      SaveChanges(db) 

     End Using 

Answer 1

我認爲你的註解是錯誤的。您將mediaId作爲Track的外鍵，但這是您的Vinyl7實體的主鍵。你的意思可能是parentMediaId對不對？

更新您的Vinyl7實體與此，它會工作：

<Key> 
    Public Overridable Property mediaId As Long  
    Public Overridable Property side As String 

    <ForeignKey("mediaId"), Required> 
    Public Overridable Property track As Track 

編輯

根據您的評論，我已經更新到1..0對1的關係。

作出了一個快速測試應用程序的工作，你能比較它與你有什麼？也許你有些額外的東西讓EF困惑？

Public Class Vinyl7 

    <Key> 
    Public Overridable Property mediaId As Long 
    Public Overridable Property side As String 

    <ForeignKey("mediaId"), Required> 
    Public Overridable Property track As Track 

End Class 

Public Class Track 
    <Key> 
    Public Property trackid As Long 
    Public Property title As String 

    Public Overridable Property Vinyl7T As Vinyl7 

End Class 

Module Module1 

    Public Class MediaRepo : Inherits DbContext 

     Public Sub New() 
     End Sub 

     Protected Overrides Sub OnModelCreating(modelBuilder As DbModelBuilder) 
     End Sub 

     Public Property Vinyl7s As DbSet(Of Vinyl7) 
     Public Property Tracks As DbSet(Of Track) 

    End Class 

    Sub Main() 
     Dim db As New MediaRepo 

     Dim vin = New Vinyl7 
     Dim track As New Track 

     track.Vinyl7T = vin 

     db.Tracks.Add(track) 
     db.SaveChanges() 

    End Sub 

End Module