Saving a nested collection with MVC 3, EF 4.1, DbContext, and AutoMapper

I am having difficulty getting a nested collection (Tags in my case) to commit back to the database after being passed into my controller. I am using EF 4.1 with the DbContext API, MVC 3, and Automapper.

My Models:

Partial Public Class Proposal
    Public Property Id As Integer
    Public Property Memo As String
    Public Property EntryDate As Nullable(Of Date)
    Public Overridable Property CategoryTags As ICollection(Of CategoryTag) = New HashSet(Of CategoryTag)

End Class

Public Class ProposalViewModel

    Public Property Id As Integer
    <DataType(DataType.MultilineText)>
    Public Property Memo As String
    <DisplayFormat(ApplyFormatInEditMode:=True, DataFormatString:="{0:d}")>
    Public Property EntryDate As Nullable(Of Date)
    Public Overridable Property CategoryTags As ICollection(Of CategoryTag) = New HashSet(Of CategoryTag)
End Class

My view uses the code from the following post to add tags: http://jarrettmeyer.com/post/2995732471/nested-collection-models-in-asp-net-mvc-3. Essentially the tags are created by adding INPUT elements with their name attribute set to "CategoryTag[0].Id", "CategoryTag[1].Id" etc... and the value of those inputs are valid Ids for Tags in my database

Lastly, my POST code:

<HttpPost()>
Public Function Edit(ByVal pvm As ProposalViewModel) As ActionResult

    Dim p As New Proposal

    p = AutoMapper.Mapper.Map(Of ProposalViewModel, Proposal)(pvm)

    If (ModelState.IsValid) Then
        db.Entry(p).State = EntityState.Modified
        db.SaveChanges()
        Return RedirectToAction("Index")
    Else
        Return View(pvm)
    End If

End Function

The pvm object is returned to my controller with the values set as I would want them to be. If I add two tags in run-time, then it has two CategoryTag objects in it's collection with the appropriate IDs. The problem is that on my call to SaveChanges, the corresponding records a开发者_如何学Gore not created in my many-to-many relation table (ProposalCategoryTag in this case).

Any idea what I'm doing wrong?

UPDATE:

I did not find anything on this, and have resorted to doing it manually like below. I dislike this method, but it works.

<HttpPost()>
Public Function Edit(ByVal pvm As ProposalViewModel) As ActionResult

    Dim p As New Proposal
    Dim tempTag As CategoryTag

    p = AutoMapper.Mapper.Map(Of ProposalViewModel, Proposal)(pvm)

    If (ModelState.IsValid) Then

        db.Proposals.Attach(p)
        db.Entry(p).Collection("CategoryTags").Load()

        For Each ct As CategoryTag In pvm.Tags

            tempTag = db.CategoryTags.Find(ct.Id)

            If tempTag Is Nothing Then
                Continue For
            End If

            If p.CategoryTags.Contains(tempTag) Then
                Continue For
            End If

            p.CategoryTags.Add(tempTag)
        Next

        db.Entry(p).State = EntityState.Modified
        db.SaveChanges()
        Return RedirectToAction("Index")
    Else

        Return View(pvm)

    End If

End Function

UPDATE:

I did not find anything on this, and have resorted to doing it manually like below. I dislike this method, but it works.

    <HttpPost()>
    Public Function Edit(ByVal pvm As ProposalViewModel) As ActionResult

        Dim p As New Proposal
        Dim tempTag As CategoryTag

        p = AutoMapper.Mapper.Map(Of ProposalViewModel, Proposal)(pvm)

        If (ModelState.IsValid) Then

            db.Proposals.Attach(p)
            db.Entry(p).Collection("CategoryTags").Load()

            For Each ct As CategoryTag In pvm.Tags

                tempTag = db.CategoryTags.Find(ct.Id)

                If tempTag Is Nothing Then
                    Continue For
                End If

                If p.CategoryTags.Contains(tempTag) Then
                    Continue For
                End If

                p.CategoryTags.Add(tempTag)
            Next

            db.Entry(p).State = EntityState.Modified
            db.SaveChanges()
            Return RedirectToAction("Index")
        Else


            Return View(pvm)

        End If

    End Function