Hi there

I am having a problem with the hierarchical model.  I have tried this in both 2007 and 2008 versions.

I had assumed that if I create the child collection using the Parent-Child property on the parent that all the children would automatically have the object reference back to the parent set.  This appears not to be the case .(Edit: some confusion when I first posted this in that I might be refering to foreign keys)

So do I need to iterate through all the children setting the UpToparentById property manually to the parent record which I just created the child collection from?  Please tell me this is not so.  If it is there is bug in the set portion of the Many to One property where it tests if the value of the property is changing.  If the private member variable for the parent is null it will error which is likely with the lazy initialization.

Dim changed as Boolean = Not Me._UpToInterviewersByInterviewerId.Equals(value)

The up shot of this which I really do not like is that if I try and reference the parent on each child using the UpToparentById property, each child will load its own copy of the parent from the database.   One of the reasons I want them all pointing at the same instance of the parent is that I have total properties on the parent which are updated from the children like in a classic order/item scenario.

I hope I have missed something here.

Cheers

Paul

Hi Paul

I've just mocked up a quick test sub and all worked as expected, the new "Parent" (Supplier) got added fine, as did the children (Products) - see if the following helps:

Private Sub TestAddChildObjects
Dim Supplier As New Suppliers
Supplier.CompanyName = "New Supplier"

Dim i As Integer
For i = 0 To 5
	Dim Product As New Products
	Product = Supplier.ProductsCollectionBySupplierID.AddNew
	Product.ProductName = "Product number " + i.ToString()
	Product.CategoryID = 1
	Product.UnitPrice = i		
Next
Supplier.Save()
End Sub

Cheers

Martin

Hi Martin

Thanks for the quick response.  I should have made myself a little clearer but it was 2am when I wrote it.  I am quite happy with the hierarchical model saving and maintaining referential integrity, that's fine and not a problem.

The problem is with the collections and entities when in memory.  The 'UpToParent' property on the child objects do not have a reference to the parent object that created them by default.  In your sample if you call Product.UpToSupplierBySupplierID.some_Memeber before or after the save it will do a lazy initialisation and create a new instance of Suppliers and load it from the database by the primary key which it gets from Product.SupplierID. 

As the product was added to a collection instantiated by an instance of  Suppliers I would expect each child to reference back to parent object that created it, not load up another instance.  If you created a collection of Products and loaded it by a query and not hierarchically then fine it should load the supplier as needed. 

If you iterate through your 5 Product objects and set the Product.UpToSupplierBySupplierID to your instance of Suppliers without referencing the property first it will error as the private member variable for the parent Supplier is null and it tries to compare it to the value you assigning it to.  If you fix the problem by forcing the property to initialise first then when you save any changes you get a StackOverflow exception.

If I you added a property to the Supplier and tried to update it from the Products records using the 'UpTo' property it would not work as you would be creating n instances of Supplier, not much good if that property was some sort of total.

Hopefully that makes my problem a little clearer. 

 Cheers

 Paul

Hi Paul

I've only skimmed your reply as I'm a bit hectic at the moment but I think the issue here is coming from the fact that you're using "xxxUpToxxx" - to the best of my knowledge EntitySpaces only saves (and therefore operates as expected) Down the tree, not up - that was the reason (I think) behind the properties being named "UpTo" so that you knew you were going "in the wrong direction" so to speak.  I'm sure one of the EntitySpaces team will give you a better/more complete answer but if you search the forum for "UpTo" you might find your answer.

Cheers, sorry it doesn't give you a more complete answer but it may point you in the right direction

Martin

Martin thanks for taking the time to answer.  I know what it is like to busy :)

Hi David

Thanks for the confirmation and I am really happy with the way the hierarchical model works and appreciate how much easier it makes writing my applications.  However I was a surprised that the creation and population of the child collection from the parent does not use the object reference that exists on the child.  In all the strongly typed hierarchical collections and datasets I have worked on prior to using Entity Spaces the reference back to the parent object has been very useful.  I can implement my own parent object property and maintain it but I was always dislike duplicating effort. 

What really did me in though was that the 'UpTo' property has a set accessor which not only errors when the private member variable for the parent object is null but also causes a stack overflow in the ApplyPreSaveKeys method if you manage to set it programmatically.  It would be nice to be able to use it but for now I'll do a workaround.  Is there an event raised when an entity is added to a collection?  I could solve my problem elegantly then.

 Cheers

 Paul

Ok for anyone who wants to maintain a reference on the child object back to the parent object here's a solution. 

 Each entity has a property called Collection which references its parent collection if any.  This is populated for entities loaded into the collection or added.  Simply add a 'Parent Object' property to the collection and set it after calling child collection property.  You'll need to cast the collection and cater for null values but it will allow you to reference the Parent object from any child object.

This sample has a PayClaimPending object which has a collection of child PayItems

Parent Object property on the Collection

#Region "Property 'ParentObj'"
    Private _ParentObj As PayClaimPending
    ''' <summary>
    '''    Reference to the Parent PayClaimPending Obj which owns this collection
    ''' </summary>
    Public Property ParentObj() As PayClaimPending
      Get
        Return _ParentObj
      End Get
      Set(ByVal Value As PayClaimPending)
        _ParentObj = Value
      End Set
    End Property

#End Region 'Property 'ParentObj'

Add something like this to your entity:

#Region "Property 'ParentCollection'"

    ''' <summary>
    '''     Typed reference to parent collection
    ''' </summary>
    Public ReadOnly Property ParentCollection() As PayItemPendingCollection
      Get
        Return DirectCast(Me.Collection, PayItemPendingCollection)
      End Get
    End Property

#End Region 'Property 'ParentCollection'


when you instantiate the child collection from the parent set the Parent Object property

payClaim.PayItemPendingCollectionByPayClaimId.ParentObj = payClaim;

then from the child objects you can reference the properties of the parent

 If Me.ParentCollection.ParentObj IsNot Nothing Then
    Me.ParentCollection.ParentObj.TotalFee += MyBase.Fee.GetValueOrDefault(0)
 End If

Also you could add a generic parent object property to the custom CollectionBase if you want to implement this in all your collections