Hi Martin and Alex, the point you raise is a good one, I did not include it in my first email because defining these common (and thereby de-facto required) queries is not a simple task: we should not include something that most journals will opt out of, and what we pick must be of general interest because it presents a burden to every journal implementor—at least morally.
My reasoning for keeping persistenceIds and arbitrary named streams separate is that persistenceIds must be supported in a fully linearizable fashion whereas named streams do not necessarily have this requirement; on the write-side it might make sense to specify that persistenceIds are only ever written to from one actor at a time, which potentially simplifies the Journal implementation. This also does not hold for named streams. Concerning types I assume that there is an implicit expectation that they work like types in Java: when I persist a ShoppingCartCreated event I want to see it in the stream for all ShoppingCartEvents. This means that the Journal needs to understand subtype relationships that in turn have to be lifted from the programming language used. It might be that this is possible, but at least it is not trivial. Is it reasonable to expect most Journal implementations to support this? One query that we might want to include generically is the ability to ask for the merged streams of multiple persistenceIds—be that deterministic or not. Another thought: there should probably be a trait JournalQuery from which the discussed case classes inherit, and we should specify that the Journal is obliged to reply to all such requests, explicitly denying those it does not implement. Regards, Roland 28 aug 2014 kl. 11:12 skrev ahjohannessen <ahjohannes...@gmail.com>: > Hi Martin, > > On Thursday, August 28, 2014 8:01:43 AM UTC+1, Martin Krasser wrote: > > In your summary, the only query command type pre-defined in akka-persistence > is QueryByPersistenceId. I'd find it useful to further pre-define other query > command types in akka-persistence to cover the most common use cases, such as: > > - QueryByStreamDeterministic(name, from, to) (as a generalization of > QueryKafkaTopic, ... and maybe also QueryByPersistenceId) > - QueryByTypeDeterministic(type, from, to) > - QueryByStream(name, fromTime) > - QueryByType(type, fromTime) > > Supporting these commands would still be optional but it would give better > guidance for plugin developers which queries to support and, more > importantly, make it easier for applications to switch from one plugin to > another. Other, more specialized queries would still remain plugin-specific > such as QueryByProperty, QueryDynamic(queryString), etc ... > > I think it is a great idea to standardize on common cases such as those you > line up, because it gives guidance and reduces one-off fragmentation among > journal APIs. It is reasonable that akka-persistence sets some sort of > standard with respect to general use cases of reading streams. > > -- > >>>>>>>>>> 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 akka-user+unsubscr...@googlegroups.com. > To post to this group, send email to akka-user@googlegroups.com. > Visit this group at http://groups.google.com/group/akka-user. > For more options, visit https://groups.google.com/d/optout. Dr. Roland Kuhn Akka Tech Lead Typesafe – Reactive apps on the JVM. twitter: @rolandkuhn -- >>>>>>>>>> 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 akka-user+unsubscr...@googlegroups.com. To post to this group, send email to akka-user@googlegroups.com. Visit this group at http://groups.google.com/group/akka-user. For more options, visit https://groups.google.com/d/optout.
