Deleted childs in a list lose their parents after being deserialized

[StefanOssendorf]

We're trying to update from Csla 8.2.9 to 9.1.0, and immediately hit an issue in a DeleteSelfChild method; we're trying to use the Parent property to get to the root object to get its Id, but it seems like this is null now. Was this intentional or is it a bug? If its intentional, what would be the proposed workaround? I'd rather not have to add an id property to every child instance and keep it in sync with the parent.

Originally posted by @ajohnstone-ks in #4759

[StefanOssendorf]

Here's a mwe to reproduce the issue:
Note: Update to 9.x to see the problem. Downgrade to 8.x to see the old (correct) behavior.

using Csla;
using Csla.Configuration;
using Csla.Serialization;
using Microsoft.Extensions.DependencyInjection;

using var sp = new ServiceCollection()
    .AddCsla()
    .BuildServiceProvider();

var rootPortal = sp.GetRequiredService<IDataPortal<Root>>();

var root = await rootPortal.FetchAsync();
//root.Delete();

root.Childs.RemoveAt(0);

//var formatter = SerializationFormatterFactory.GetFormatter(sp.GetRequiredService<ApplicationContext>()); // CSLA 8.X
var formatter = sp.GetRequiredService<ISerializationFormatter>(); // CSLA 9.x+

var data = formatter.Serialize(root);

var deserialized = formatter.Deserialize(data);

_ = deserialized; // here the child in the Childs.DeletedList should still have it's parent set

[CslaImplementProperties, Serializable]
public partial class Root : BusinessBase<Root> {
    public partial Guid Id { get; set; }
    public partial FooChilds Childs { get; set; }

    [Fetch]
    private async Task Fetch([Inject] IChildDataPortal<FooChilds> fooPortal) {
        Id = Guid.NewGuid();
        Childs = await fooPortal.FetchChildAsync();
    }

    [Update]
    [DeleteSelf]
    private async Task DeleteSelf() {
        await FieldManager.UpdateAllChildrenAsync();
    }
}


[Serializable]
public partial class FooChilds : BusinessListBase<FooChilds, FooChild> {
    [FetchChild]
    private async Task FetchChild([Inject] IChildDataPortal<FooChild> fooPortal) {
        for (int i = 0; i < 3; i++) {
            Add(await fooPortal.FetchChildAsync());
        }
    }
}

[CslaImplementProperties, Serializable]
public partial class FooChild : BusinessBase<FooChild> {
    public partial Guid? Id { get; set; }

    [FetchChild]
    private void CreateChild() {
        Id = Guid.NewGuid();
    }

    [DeleteSelfChild]
    private void DeleteSelfChild() {
        Id = null;
    }

    [UpdateChild]
    private void UpdateChild() {
        _ = this;
    }
}

[StefanOssendorf]

After some digging I found the changes which caused this change in behavior:
#3895 with #3955
We have to provide the old behavior for deleted childs. The Deserialized hook is still there. So maybe we just have to undo some of the PR?

[StefanOssendorf]

@ajohnstone-ks should be fixed with CSLA 10.

@rockfordlhotka
I think I should backport that to 9.X as well?

[rockfordlhotka]

I think we should

@ajohnstone-ks should be fixed with CSLA 10.

@rockfordlhotka
I think I should backport that to 9.X as well?

[ajohnstone-ks]

@rockfordlhotka @StefanOssendorf Thank you both!