I concur with what Martin said. /Patrik
On Sun, Mar 30, 2014 at 11:21 PM, Raman Gupta <[email protected]> wrote: > I would stick with a "version" attribute on the events, which then gives > you the flexibility to use promotion or explicit version handling on a > case-by-case basis. > > Maybe one way to handle event version promotion with akka-persistence > would be to implement a kind of "recovery roll-forward" as a variation of > the "Recovery Status" pattern described at > http://doc.akka.io/docs/akka/snapshot/scala/persistence.html#Recovery_status > . > > As the processor recovers and receives each v1 event, it promotes it to a > v2 event and resends it to itself (is this ok or will this result in a > potentially huge mailbox?). > > The v1 event is then marked as deleted. As described in the "recovery > status" pattern, any new v2 events received during recovery need to be > stashed after recovery (and before "FIRST") to maintain the ordering. > However, the processor should differentiate between v2 events that were > promoted and thus should not be stashed vs new v2 events that should be > stashed. I think one possibility is to create a "fromVersion" event > attribute, which can then be used by the processor to skip stashing if > fromVersion < currentVersion. > > Related: 1) Snapshots should be turned off for the promotion > (SnapshotSelectionCriteria.None) to ensure the pre-snapshot v1 events are > promoted as well. 2) Views should probably use the fromVersion attribute > intelligently as well. > > Thoughts? > > Regards, > Raman > > On Sunday, March 30, 2014 9:16:42 AM UTC-4, rrodseth wrote: > >> Thanks, Martin and Roger. Would anyone else care to weigh in on this? >> Strategies for migration? >> >> DDD/ES with Akka persistence is just something I'm reading about at this >> point (and dying to use). It does feel like a game-changer, but this issue >> of data model migration is a big unknown for me. >> >> Thanks! >> >> >> On Thu, Feb 27, 2014 at 1:05 AM, Roger Alsing <[email protected]> wrote: >> >>> There is a quite nice approach that Rickard Öberg uses for Qi4J. >>> He uses _two_ versions for each message. >>> "old" and "new" >>> old events needs to be able to be promoted to new events. >>> so each time you deploy, you promote old messages to new messages, and >>> the system will run with only the new version. >>> this way, you never ever have to have code for more than two versions at >>> any given time. >>> >>> Not sure how this plays with Akka persistence, but I Think its a nice >>> approach since you dont have to deal with 10 year old versions in long >>> lived systems. >>> (Then again, people may object to the fact that you need to tansform old >>> to new and that it might alter the history.. but thats a different story :) >>> ) >>> >>> >>> Den onsdagen den 26:e februari 2014 kl. 18:53:49 UTC+1 skrev rrodseth: >>> >>>> Now that we're getting excited about using akka persistence for >>>> event-sourced DDD applications, can anyone provide any insights or >>>> resources about handling versioning? Anything specific to akka persistence? >>>> For example I have a book (produced by Microsoft) that talks about >>>> mapping/filtering events in the infrastructure before they reach the >>>> domain. How would we do that with akka persistence? >>>> >>>> Thanks in advance. >>>> >>> -- >>> >>>>>>>>>> Read the docs: http://akka.io/docs/ >>> >>>>>>>>>> Check the FAQ: http://akka.io/faq/ >>> >>>>>>>>>> Search the archives: https://groups.google.com/ >>> group/akka-user >>> --- >>> You received this message because you are subscribed to the Google >>> Groups "Akka User List" group. >>> To unsubscribe from this group and stop receiving emails from it, send >>> an email to [email protected]. >>> To post to this group, send email to [email protected]. >>> >>> Visit this group at http://groups.google.com/group/akka-user. >>> For more options, visit https://groups.google.com/groups/opt_out. >>> >> >> -- > >>>>>>>>>> Read the docs: http://akka.io/docs/ > >>>>>>>>>> Check the FAQ: > http://doc.akka.io/docs/akka/current/additional/faq.html > >>>>>>>>>> Search the archives: https://groups.google.com/group/akka-user > --- > You received this message because you are subscribed to the Google Groups > "Akka User List" group. > To unsubscribe from this group and stop receiving emails from it, send an > email to [email protected]. > To post to this group, send email to [email protected]. > Visit this group at http://groups.google.com/group/akka-user. > For more options, visit https://groups.google.com/d/optout. > -- Patrik Nordwall Typesafe <http://typesafe.com/> - Reactive apps on the JVM Twitter: @patriknw JOIN US. 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