[jira] [Resolved] (BEAM-5307) Allow injection of state in DoFn.FinishBundle

["Kenneth Knowles (JIRA)" <ji...@apache.org>]

     [ https://issues.apache.org/jira/browse/BEAM-5307?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel ]

Kenneth Knowles resolved BEAM-5307.
-----------------------------------
       Resolution: Duplicate
    Fix Version/s: Not applicable

> Allow injection of state in DoFn.FinishBundle
> ---------------------------------------------
>
>                 Key: BEAM-5307
>                 URL: https://issues.apache.org/jira/browse/BEAM-5307
>             Project: Beam
>          Issue Type: Improvement
>          Components: sdk-java-core
>            Reporter: Sander Ploegsma
>            Assignee: Kenneth Knowles
>            Priority: Major
>             Fix For: Not applicable
>
>
> Example use case: a stateful {{DoFn}} that requires persisting its state to an external database. Instead of writing to the external database for each element, it is much more efficient to flush the state every once in a while, or when cleaning up.
> Currently, this is not possible because the {{@StateId}} injection is only available in processing functions and timers. [This|https://stackoverflow.com/questions/51789776/calculating-deltas-in-apache-beam-using-stateful-processing] might be a workaround, but I'm not even sure if it works.
> Instead, by allowing the use of {{@StateId}} inside a {{@FinishBundle}} function, we can make sure the internal state is persisted in all scenarios:
> {code:java}
> @FinishBundle
> public void flush(FinishBundleContext context, @StateId("myState") ValueState<StateObj> state) {
>     repository.save(state.read());
> }
> {code}
>  



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