Hi, On 21 August 2014 at 20:28:35, Prakhyat Mallikarjun ([email protected]) wrote:
Patrik, Thanks. You have given good directions to me. Most of the apps will do queries or searches specific to domain or business. If business specific complex queries/searches are better solved in the backend data store, why akka persistence "PersistenceView" is required and should be still part of akka persistence?I am not doubting "PersistenceView" but want to understand why one would choose "PersistenceView" in design over simpler data store? The PersistentView is not a data store in any sense of the word. It is a way to replay events from the journal in a simple way. Even if it is enhanced to support streaming of multiple id's or topics it is still can not be a specialized query model. PersistentView can be used to feed your data into a query model (maybe a normal SQL database or what fits your queries the best). B/ Akka persistence is making write side of my application very simple to configure and implement. But when it comes to complex querying/searching I find myself lost. I find no simple solution. Thanks to Greg I have one solution "Projection" but still I am evaluating whether it will fit our app. I have questions to answer myself whether to use cassandra event store or gregs event store. If I use cassandra event store I wont be able to use Projections.....its getting complex for me..... I am looking for most simple solution for 'Q' in CQRS from akka persistence with DDD approach. If team is working on solutions, when can we expect? -Prakhyat M M On Thursday, 21 August 2014 22:14:03 UTC+5:30, Patrik Nordwall wrote: On Wed, Aug 20, 2014 at 9:33 AM, Prakhyat Mallikarjun <[email protected]> wrote: Team, Consider I have domain model Bank Customer's Account's Bank object will have many customers. Every customer will have multiple accounts. Consider I implement the above model using akka persistence. For the sake of discussion consider I make each as different Aggregate Roots using PersistentActor's. I want to implement a query : Give my all customers whose balance is less then 100$. Do you mean, 1. Create one PersistentView XYZ. 2. This XYZ will listen from all 3 AR's. 3. PersistentView XYZ will replicate these events as state to some DB consider cassandra. 4. Client will query directly cassandra to find "all customers whose balance is less then 100$". Is my understanding correct? Yes, maybe. If you model each customer as a PersistentActor you have to setup one PersistentView for each customer, since currently a PersistentView instance can only consume events from one PersistentActor instance. Same thing with accounts. We are currently discussing (in several threads) how we can improve PersistentView. Perhaps it should be able to consume events from several PersistentActors. Perhaps we should add another thing called topic, which PersistentActor can publish events to, and a PersistentView can consume events from. We don't know yet. We are collecting input. Martin has also suggested that this type of scenario is better solved in the backend data store. In this case a program would transform the events in Cassandra by using Cassandra API:s and save another representation in Cassandra (or somewhere else). Clients can then query directly. No PersistentView involved. /Patrik If not, can you let me know how to achieve this using PersistentView? -Prakhyat M M On Tuesday, 19 August 2014 22:49:14 UTC+5:30, Martin Krasser wrote: On 19.08.14 18:48, delasoul wrote: As I am no Spark expert - will it be used only as kind of messaging(streaming) middleware to sync write and read store or also to somehow change/merge/ filter the events it gets/pulls from the write store usually, to process (transform/aggregate/filter/...) these events. or is this all done via the plugin for PersistentViews? (I guess it has to be like this, otherwise using only one backend store cannot be supported?) thanks, michael On Tuesday, 19 August 2014 17:48:16 UTC+2, Martin Krasser wrote: On 19.08.14 17:41, Ashley Aitken wrote: On Tuesday, 19 August 2014 19:33:55 UTC+8, Martin Krasser wrote: If so, it sounds like a great solution but why would that require an extension to the Akka Persistence design/API? Because transformed/joined/... event streams in backend store on the read side must be consumable by PersistentViews (for creating read models). I still see this backend store to maintain changes (= transformed/joined/... events) instead of current state. I am sorry I still don't see this. This suggests to me that spark is talking directly to the read model datastore (e.g. graph database, MongoDB, SQL database). So are you suggesting: 1. journal -> spark -> Akka actors (like PersistentView) -> read model data store or 2. journal -> spark -> read model data store (like graph database, MongoDb, SQL database) -> Akka actors <- Queries I was suggesting 2. I see PersistentView(for generalised topics) as the glue between the Akka journal (write store) and read stores (1.). Thanks for your patience. Cheers, Ashley. -- >>>>>>>>>> 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. -- Martin Krasser blog: http://krasserm.blogspot.com code: http://github.com/krasserm twitter: http://twitter.com/mrt1nz -- >>>>>>>>>> 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. -- Martin Krasser blog: http://krasserm.blogspot.com code: http://github.com/krasserm twitter: http://twitter.com/mrt1nz -- >>>>>>>>>> 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 - Reactive apps on the JVM Twitter: @patriknw -- >>>>>>>>>> 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. -- Björn Antonsson Typesafe – Reactive Apps on the JVM twitter: @bantonsson -- >>>>>>>>>> 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.
