Self Referencing Hierarchy with Null Guids crashes

AKaplan posted on Wednesday, November 24, 2010

I have a situation where I have a self referencing hierarchy table with guids. In the ParentID there has to be nulls for it to be recognized as the top level parent. When I run this through my csla object, it crashes at populating the object such as LoadProperty(of Guid)(_ParentIDProperty,data.ParentID) with an error of NullReferenceException throw (I believe). Now I've tried to solve this with declaring my ParentID as a Nullable(of Guid) with no success. Does anyone else have a solution? This clsa build is 3.6

am_fusion replied on Wednesday, November 24, 2010

I am not so sure what your actual problem may be (your solution of making the ParentId nullable should work).

A couple of suggestions though:

• maybe use empty guid instead of null to represent a root level entity in the hierarchy
• are you sure you need to populate your BO with this value... shouldn't the ParentId field only be needed in the database?  The child, can get the parent's ID through the parent property, so all entities need only have their own ID.

AKaplan replied on Wednesday, November 24, 2010

ok in my BO I have this setup...

#region "Business Logic"

 Private Shared _IDProperty As PropertyInfo(Of Guid) = RegisterProperty(Of Guid)(GetType(ProductCategory), New PropertyInfo(Of Guid)("ID", "ID", Guid.NewGuid))

    Private _ID As Nullable(Of Guid) = _IDProperty.DefaultValue

    Private Shared _ParentIDProperty As PropertyInfo(Of Guid) = RegisterProperty(Of Guid)(GetType(ProductCategory), New PropertyInfo(Of Guid)("ParentID", "ParentID", Guid.Empty))

    Private _ParentID As Nullable(Of Guid) = _ParentIDProperty.DefaultValue

<System.ComponentModel.DataObjectField(True, True)> _

 Public ReadOnly Property ID() As Guid

        Get

            Return GetProperty(Of Guid)(_IDProperty, _ID)

        End Get

    End Property

    <System.ComponentModel.DataObjectField(True, True)> _

    Public Property ParentID() As Nullable(Of Guid)

        Get

            Return GetProperty(Of Guid)(_ParentIDProperty)

        End Get

        Set(ByVal value As Nullable(Of Guid))

            SetProperty(Of Guid)(_ParentIDProperty, value)

        End Set

    End Property

#End Region 

#region "Child Data Logic"

Private Sub Child_Fetch(ByVal data As CK.Linq.ProductCategory)

        LoadProperty(Of Guid)(_IDProperty, data.ID)

It crashes here when retrieving data from the DB if it has a null 

        LoadProperty(Of Guid)(_ParentIDProperty, data.ParentID)

        LoadProperty(Of String)(_name, data.Name)

        LoadProperty(Of String)(_description, data.Description)

        LoadProperty(Of String)(_imageUrl, data.ImageUrl)

        LoadProperty(Of ProductList)(_productlist, Productlist.GetProductList(data.XrefProductCategories.ToArray))

    End Sub

#End Region

am_fusion replied on Wednesday, November 24, 2010

very odd... the only thing I can think of is your LoadProperty generic type is (of Guid) and might need to be (of nullable(of guid)):

LoadProperty(Of nullable(of Guid))(_ParentIDProperty, data.ParentID)

also, your register property static call should be:

 Private Shared _ParentIDProperty As PropertyInfo(Of nullable(of Guid)) = RegisterProperty(Of nullable(Of Guid))(GetType(ProductCategory), New PropertyInfo(Of nullable(Of Guid))("ParentID", "ParentID", Guid.Empty))

AKaplan replied on Wednesday, November 24, 2010

I change to your solution because that was a great idea and also added.

 Private Sub Child_Fetch(ByVal data As CK.Linq.ProductCategory)

        LoadProperty(Of Guid)(_IDProperty, data.ID)

        If data.ParentID.HasValue = True Then

            LoadProperty(Of Nullable(Of Guid))(_ParentIDProperty, data.ParentID)

        Else

            LoadProperty(Of Nullable(Of Guid))(_ParentIDProperty, Guid.Empty)

        End If

        LoadProperty(Of String)(_name, data.Name)

        LoadProperty(Of String)(_description, data.Description)

        LoadProperty(Of String)(_imageUrl, data.ImageUrl)

        LoadProperty(Of ProductList)(_productlist, Productlist.GetProductList(data.XrefProductCategories.ToArray))

    End Sub

I feel as if I'm getting closer.. now I have no errors with no results... oh btw.. this is binding to a very plain treeview.