@PreserveOnRefresh doesn't preserve UI scoped beans

[edler-san]

The behaviour of @PreserveOnRefresh+CDI within Vaadin 14 differs from that of Vaadin 8. In the current version scope'd beans can differ after a refresh which did not happen in V8.

Related: vaadin/spring#473

[denis-anisimov]

See the user level explanation here:
vaadin/spring#473 (comment)

[denis-anisimov]

The solution is: UIScope should not work as it's expected here. See explanation above.

But there is future way to do it

• via Document how to preserve beans with @RouteScope when migrating from v7/v8 flow#6395
• use proper scope to make it work.

There is already RouteScoped annotation which should be used for this.
But its implementation is UIScope based. So it won't work. And this is a bug.
We should make it preserving scoped beans on refresh if the owner has @PreserveOnRefresh annotation.

So the implementation should be changed.
See the implementation details here: vaadin/spring#263 (comment)
They are quire similar in Spring. It should be done in the same way.

Also it would be good (it's not clear whether this is feasible) to avoid using an additional qualifier for the scope owner: do it somehow in a way similar to Spring. But may be this is not possible.

[kumm]

I have a simple POC to support current V14 behaviour.
The addon preserve ( by moving from the old UIScoped store to the new ) the route context for preserved route owners ( components in the preserved route chain).
This approach need an event fired by vaadin before moving the components to the new UI on reload.

As it said it is not what users expect, but at least it is in pair with current @PreserveOnReload.

If vaadin will support preserve on reload for the entire UI by moving all components to a new UI, then all UI scoped, and route scoped beans can be preserved same way. In fact it would be a little simpler.

It can be found here: kumm@f4d0910, kumm/flow@c7e66c3

[denis-anisimov]

see #369

[pleku]

Closing this as a won't fix, as the issue is addressed in https://github.com/vaadin/cdi/releases/tag/13.0.0.alpha1 (version for Vaadin 21) with changing the behavior of @RouteScoped.

We don't have plans at the moment for backporting the fix to the Vaadin 14 version of CDI add-on as it is a behavior change and could affect existing applications. If someone needs this badly for Vaadin 14, we could maybe make a new intermediate version where the feature is backported, and then users can opt-in to use it. Please comment here if that would be desired.