Entity Framework Update Foreign Key constraint may cause multiple cascade paths - sql

Question

I'm working on a project that is using entity framework and I'm getting the following error when I try and update my database.
Introducing FOREIGN KEY constraint 'FK_dbo.VisualManualWebPageFiles_dbo.VisualManualHeaders_VisualManualHeaderID' on table 'VisualManualWebPageFiles' may cause cycles or multiple cascade paths. Specify ON DELETE NO ACTION or ON UPDATE NO ACTION, or modify other FOREIGN KEY constraints.
Could not create constraint.
Here are the classes that are being used for this.
First With a VisualManualHeader class.
<Table("VisualManualHeaders")>
Public Class VisualManualHeader
<Key>
Public Property VisualManualHeaderID As Integer
<Required>
Public Property Name As String
Public Overridable Property VisualManualPages As ICollection(Of VisualManualPage)
Public Overridable Property VisualManualWebPageFiles As ICollection(Of VisualManualWebPageFile)
End Class
Then a VisualManualHeader has the associated VisualManualPages with it like the following.
<Table("VisualManualPages")>
Public Class VisualManualPage
Enum VisualManualPageType
VIDEO
IMAGE
TEXT
WEBPAGE
End Enum
<Key>
Public Property VisualManualPageID As Integer
<Required>
Public Property Title As String
Public Property VisualManualHeaderID As Integer
<ForeignKey("VisualManualHeaderID")>
Public Overridable Property VisualManualHeader As VisualManualHeader
Public Property Content As String
Public Property PageType As VisualManualPageType
Public Overridable Property VisualManualWebPageFiles As ICollection(Of VisualManualWebPageFile)
End Class
The pages can then have many VisualManualWebPageFiles associated to the page.
<Table("VisualManualWebPageFiles")>
Public Class VisualManualWebPageFile
<Key>
Public Property VisualManualWebPageFileID As Integer
<Required>
Public Property VisualManualHeaderID As Integer
<ForeignKey("VisualManualHeaderID")>
Public Overridable Property VisualManualHeader As VisualManualHeader
<Required>
Public Property VisualManualPageID As Integer
<ForeignKey("VisualManualPageID")>
Public Overridable Property VisualManualPage As VisualManualPage
Public Property FileLocation As String
End Class
I have a feeling the problem is in the VisualManualWebPageFiles class due to the foreign key of the VisualManualHeader as if I remove this I can then update my project.
Thanks.

Answer 1

I think the problem lies with the association of the entity classes. Taking a look at your code seems that VisualManualHeader and VisualManualPage are in Many-To-Many relation; i.e. one instance of VisualManualHeader can be associated with many instances of VisualManualPage, and the the reverse is also true.
If that is indeed the case then, the relation between 2 classes are represented in VisualManualWebPageFile correctly and there is no need of keeping unnecessary properties in both VisualManualHeader, and VisualManualPage. I have tried to remove the same as follows:
VisualManualHeader
<Table("VisualManualHeaders")>
Public Class VisualManualHeader
<Key>
Public Property VisualManualHeaderID As Integer
<Required>
Public Property Name As String
Public Overridable Property VisualManualWebPageFiles As ICollection(Of VisualManualWebPageFile)
End Class
VisualManualPage
<Table("VisualManualPages")>
Public Class VisualManualPage
Enum VisualManualPageType
VIDEO
IMAGE
TEXT
WEBPAGE
End Enum
<Key>
Public Property VisualManualPageID As Integer
<Required>
Public Property Title As String
Public Property Content As String
Public Property PageType As VisualManualPageType
Public Overridable Property VisualManualWebPageFiles As ICollection(Of VisualManualWebPageFile)
End Class
VisualManualWebPageFile
<Table("VisualManualWebPageFiles")>
Public Class VisualManualWebPageFile
<Key>
Public Property VisualManualWebPageFileID As Integer
<Required>
Public Property VisualManualHeaderID As Integer
<ForeignKey("VisualManualHeaderID")>
Public Overridable Property VisualManualHeader As VisualManualHeader
<Required>
Public Property VisualManualPageID As Integer
<ForeignKey("VisualManualPageID")>
Public Overridable Property VisualManualPage As VisualManualPage
Public Property FileLocation As String
End Class

Answer 2

You are basically correct. The WebPageFiles does not need a reference to the ManualHeader table - and it actually could cause errors.
Example:
ManualPage ID 10 is owned by ManualHeader 1. You add WebPageFiles ID 15 with ManualPage 1 - but there is nothing stopping you setting WebPageFiles.ManualHeaderID to 3 as long as ManualHeader 3 exists. You now have a WebPageFile which a bit confused about who its grandparent is.
The correct way is to set the parent ID only (ManualPage). This parent will contain the ID of its own parent (ManualHeader) and so the child (WebPageFile) can unambiguously fing its grandparent via its parent.