Delete Child From Aggregate Root

mikehearn · February 1st, 2012, 10:04 AM

I am trying to delete a child object from an aggregate root but I keep receiving an error saying the foreign key is null.

I am using EF and the repository pattern and saving my aggregate root like below.

Code:

Dim product As New ProductInfo
product = _productRepository.FindBy(1).FirstOrDefault
If (product IsNot Nothing) Then
    stockTransfer.Remove(product.StockKeys.Where(Function(x) x.Id = 1).FirstOrDefault)
End If

_stockTransferRepository.Save(stockTransfer)

I have read the following two links.

http://blogs.msdn.com/b/dsimmons/arc...ps-in-ef4.aspx

http://mocella.blogspot.com/2010/01/...ect-graph.html

The links suggest to use DeleteObject to manually delete the child from the parent. Because when I remove the child from the parents collection it just removes the relationship but still leaves the record in the database.

My Save method in the repository is expecting an aggregate root. Will I need to create a new Save method inside my repository that passes in the aggregate root and the child object and then delete the child object manually while saving the aggregate root like below.

Code:

Public Sub SaveParentAndRemoveChild(entity As StockTransfer, item As StockTransferItem) Implements IStockTransferRepository.SaveParentAndRemoveChild
            GetObjectContext().DeleteObject(item)
            MyBase.Save(entity)
End Sub

Any suggestions would be great.

Mike

elbandit · February 25th, 2012, 06:29 AM

Hi mike,

Thanks for reading the book!

This is the issue you have http://stackoverflow.com/questions/2...-delete-it-why

Have a read of the answer in this post as I think it could solve your issue http://social.msdn.microsoft.com/For...3-bac661331788

I am not much of an EF expert I'm afraid. This is really easy to do in NHiberate though!

Cheers
Scott

mikehearn · February 27th, 2012, 05:49 AM

Thank you for your response.

I am able to delete the child object using the DeleteObject() method but I was wondering which is the best way to follow DDD with deleting child objects with EF.

Should I create another method in my repository like DeleteChild() and call this before I use the save method?

CoolKiwiBloke · September 6th, 2012, 01:03 AM

Where did you get to with this? I've also run into the same issue, and even adding a DeleteChild method on the repository is tricky because all the methods thereafter expect an AggregateRoot which its not.

I would be curious to know how this is done in NHibernate because it must be translatable.

I'm coming to the conclusion that a generic delete method needs to be added to the UOW which can delete any object. Practical, but defeats the architecture somewhat.

I had to do something similar for creating entities, since entities need to be created by the calling CreateObject for the data context to register them I added T CreateObject<t>() to my UOW to handle non-aggreate root entities.