First of all, I would like to thank you for the great blog post and code example!

Second, I have followed many blog posts about Akka and event sourcing and all of them use in-memory storage for storing the current state of the application. In your case it is the blog posts lists, what happens in case when the list is getting very big, like millions of posts, how does Akka handle it?

As the title suggests there is an issue when executing the put request. Full stack trace

java.lang.ClassCastException: Cannot cast com.spr.blog.BlogEntity$PostUpdated to scala.util.Either at java.lang.Class.cast(Class.java:3369) at scala.concurrent.Future.$anonfun$mapTo$1(Future.scala:495) at scala.util.Success.$anonfun$map$1(Try.scala:251) at scala.util.Success.map(Try.scala:209) at scala.concurrent.Future.$anonfun$map$1(Future.scala:287) at scala.concurrent.impl.Promise.liftedTree1$1(Promise.scala:29) at scala.concurrent.impl.Promise.$anonfun$transform$1(Promise.scala:29) at scala.concurrent.impl.CallbackRunnable.run(Promise.scala:60) at scala.concurrent.BatchingExecutor$Batch.processBatch$1(BatchingExecutor.scala:63) at scala.concurrent.BatchingExecutor$Batch.$anonfun$run$1(BatchingExecutor.scala:78) at scala.runtime.java8.JFunction0$mcV$sp.apply(JFunction0$mcV$sp.java:12) at scala.concurrent.BlockContext$.withBlockContext(BlockContext.scala:81) at scala.concurrent.BatchingExecutor$Batch.run(BatchingExecutor.scala:55) at scala.concurrent.Future$InternalCallbackExecutor$.unbatchedExecute(Future.scala:864) at scala.concurrent.BatchingExecutor.execute(BatchingExecutor.scala:106) at scala.concurrent.BatchingExecutor.execute$(BatchingExecutor.scala:103) at scala.concurrent.Future$InternalCallbackExecutor$.execute(Future.scala:862) at scala.concurrent.impl.CallbackRunnable.executeWithValue(Promise.scala:68) at scala.concurrent.impl.Promise$DefaultPromise.$anonfun$tryComplete$1(Promise.scala:284) at scala.concurrent.impl.Promise$DefaultPromise.$anonfun$tryComplete$1$adapted(Promise.scala:284) at scala.concurrent.impl.Promise$DefaultPromise.tryComplete(Promise.scala:284) at akka.pattern.PromiseActorRef.$bang(AskSupport.scala:581) at akka.pattern.PipeToSupport$PipeableFuture$$anonfun$pipeTo$1.applyOrElse(PipeToSupport.scala:22) at akka.pattern.PipeToSupport$PipeableFuture$$anonfun$pipeTo$1.applyOrElse(PipeToSupport.scala:21) at scala.concurrent.Future.$anonfun$andThen$1(Future.scala:531) at scala.concurrent.impl.Promise.liftedTree1$1(Promise.scala:29) at scala.concurrent.impl.Promise.$anonfun$transform$1(Promise.scala:29) at scala.concurrent.impl.CallbackRunnable.run(Promise.scala:60) at akka.dispatch.BatchingExecutor$AbstractBatch.processBatch(BatchingExecutor.scala:55) at akka.dispatch.BatchingExecutor$BlockableBatch.$anonfun$run$1(BatchingExecutor.scala:92) at scala.runtime.java8.JFunction0$mcV$sp.apply(JFunction0$mcV$sp.java:12) at scala.concurrent.BlockContext$.withBlockContext(BlockContext.scala:81) at akka.dispatch.BatchingExecutor$BlockableBatch.run(BatchingExecutor.scala:92) at akka.dispatch.TaskInvocation.run(AbstractDispatcher.scala:41) at akka.dispatch.ForkJoinExecutorConfigurator$AkkaForkJoinTask.exec(ForkJoinExecutorConfigurator.scala:49) at akka.dispatch.forkjoin.ForkJoinTask.doExec(ForkJoinTask.java:260) at akka.dispatch.forkjoin.ForkJoinPool$WorkQueue.runTask(ForkJoinPool.java:1339) at akka.dispatch.forkjoin.ForkJoinPool.runWorker(ForkJoinPool.java:1979) at akka.dispatch.forkjoin.ForkJoinWorkerThread.run(ForkJoinWorkerThread.java:107)

Hello ,

In the sample code sending events on event stream and persisting state is not in a single transaction , this may lead into missing events for upstream for making a consistent view state(CQRS).

How do we tackle this.

Hello,

I am new to Event Sourcing and CQRS.

In the example if i have a command which says merge two blog and make a new blow which constains all posts of blog 1 and blog 2 and mark other two blogs as defunct.

In this kind of scenario, how should i implement Event Sourcing and CQRS and maintain consistency