Merging (or converting between) changesets from a SourceList and changesets from a SourceCache

[ds090525]

Hello, I am wondering how to merge changesets from SourceList and SourceCache. I know that if both collections are of the same type (e.g. both are SourceLists or both are SourceCaches) I can use various operators like Or(), Merge() or MergeChangeSets() depending on what I want to achieve. However, if the types are different, I am not sure how to proceed.

My actual use case is also a little more complicated. I have a SourceCache<MyViewModel, Guid> and a SourceCache<MyOtherViewModel, Guid> where each OtherViewModel has a SourceList<ChildViewModel> and I am actually trying to merge the changesets of the nested child view models with the changesets from the first SourceCache.

public interface IViewModel
{
    Guid Id { get; }
}

public class MyViewModel : IViewModel
{
    public Guid Id { get; } = Guid.NewGuid();
}

public class MyOtherViewModel : IViewModel
{
    private SourceList<ChildViewModel> _childrenSource = new();
    public Guid Id { get; } = Guid.NewGuid();

    public IObservable<IChangeSet<ChildViewModel>> ConnectChildren() => _childrenSource.Connect();
}

public class ChildViewModel : IViewModel
{
    public Guid Id { get; } = Guid.NewGuid();
}

The way how I am trying to merge them is as follows:

SourceCache<MyViewModel, Guid> _firstCache = new(x => x.Id);
SourceCache<MyViewModel, Guid> _secondCache = new(x => x.Id);
SourceCache<MyOtherViewModel, Guid> _thirdCache = new(x => x.Id);

var mergedChangeSets =
    _firstCache.Connect().Transform(x => x as IViewModel)
    .Or(_secondCache.Connect().Transform(x => x as IViewModel))
    // this will not compile because it produces IObservable<IChangeSet<IViewModel>> instead of IObservable<IChangeSet<IViewModel, Guid>>
    .Or(_thirdCache.Connect().MergeManyChangeSets(x => x.ConnectChildren().Transform(x => x as IViewModel)));

There is no overload of MergeManyChangeSets() that allows specifiying a key selector and when I tried to use Transform() with a key selector it was impossible because that requires the source to already be IObservable<IChangeSet<IViewModel, Guid>>.

Alternatively, I don't actually care if mergedChangeSets contains the keys or not, so I wouldn't mind if it was just an IObservable<IChangeSet<IViewModel>>.

I might be able to get something that compiles if I use ToCollection() but that will break the changeset-awareness and I cannot have that because I want to apply further operators to mergedChangeSets later.

I also know that I could turn the SourceList in MyOtherViewModel to a SourceCache, but in my real app I cannot do that due to some other issues.

[JakenVeina]

Seems like you're looking to collect ALL of your view models, of all different types, into one central collection? Perhaps to dispose them all?

Since you're using GUIDs, you're correctly interpreting that you can just merge all the streams together with native RX, as there's no real risk of key overlap. (At least, I THINK that's what the .Or() operator does, right? It's equivalent to a .Merge()?) Anyway, there's an operator you can use to just convert a list stream into a keyed stream, .AddKey(), since you HAVE a usable key.

var mergedChangeSets =_firstCache.Connect()
        .Transform(x => x as IViewModel)
    .Or(_secondCache.Connect()
        .Transform(x => x as IViewModel))
    .Or(_thirdCache.Connect()
        .MergeManyChangeSets(x => x.ConnectChildren()
            .AddKey(x => x.Id)
            .Transform(x => x as IViewModel)));

[ds090525]

Thanks, I didn't know about AddKey().