Support filtering in `store.Store.List(ctx)`

[gonzolino]

Summary

When listing objects in a store.Store it is currently not possible to filter the results. The List(context.Context) method always lists all objects. The method should be extended to something like List(ctx context.Context, opts ...ListOption) to support filtering.

See List(context.Context, ObjectList, ...ListOption) in controller-runtime as inspiration.

Basic example

How to filter objects currently:

all, err := store.List(ctx)
if err != nil {
	return nil, err
}
filtered []E
sel := labels.SelectorFromSet(labels.Set(map[string]string{"foo": "bar"}))
for _, obj := range all {
	if !sel.Matches(labels.Set(obj.Metadata.Labels)) {
		continue
	}
	filtered = append(filtered, obj)
}
return filtered, nil

How to filter with the new List(ctx context.Context, opts ...ListOption) method:

filtered, err := store.List(ctx, store.MatchingLabels{"foo": "bar"})
return filtered, err

Motivation

Filtering the list of objects is a common use-case and always fetching all objects in the store and then filtering in the client is inefficient. Supporting filtering directly in the store simplifies client code using store.Store, and allows to build optimizations into the store (e.g. indexing labels, caching objects).

This should simplify the implementation of ironcore-dev/ceph-provider#857

[gonzolino]

I prepared two draft PRs to show usage of the new filtering mechanism:

• ceph-provider: Use native filtering of store.Store ceph-provider#883
• libvirt-provider: Use native filtering of store.Store libvirt-provider#740