Hi Ronnie, Have you checked out the migration implementation in Streamflow? If not, get the code here:
http://waybuild.gotdns.com/nexus/content/repositories/snapshots/se/streamsource/streamflow/streamflow-web/1.2-SNAPSHOT/ and look for se.streamsource.streamflow.web.assembler se.streamsource.streamflow.web.application.migration (and possibly more files...) Hope that helps Cheers, Marc On 26/10/2010, at 16.11, Ronnie Nessa wrote: > Hi. > > I have a problem I´m not able to find a solution for. Hopefully someone on > this list can help. > > Background: > In our system we have a use case where some entities need to be initialized > (created or updated) at the startup of the system. Mainly this happens at the > first startup, but also sometimes the entities needs to be updated with new > values for some properties. To support this usecase I need to be able to > query the entitystore to find out if the entities I wan´t to create already > exist or not. My initial solution for this was to add a mixin with a property > i called "readableIdentifier" to the entity-types that I needed to be able to > bootstrap. I then do a conditional create based on wether or not I can find > an entity with the correct "readableIdentifier". This kind of works, but the > conditional create seems quite brittle as I haven´t found a way to make the > "readableIdentifier" unique. So then the other day I was reading some API, > and I found that doing unitofwork.create(MyEntity.class, > "myReadableIdentifier") probably was a better way to support my use case. Why > I didn´t see this before is a bit annoying, but anyway, now I´m in the > situation where I want´t to change my code to use this new approach but I > also have to support the datastore we have in test already. > > My initial thoughts was to use the Migration api to change the identity of > the entities in question. Since EntityMigrationOperation doesn´t support > changing the identiy of an entity (which makes sense since we also need to > change all references to the entity), I decided to use an implementation of > MigrationOperation. The problem is I cannot figure out how to do the actual > implementation. The problem is that the upgrade-method on MigrationOperation > only accept StateStore and Migrator as parameters. These interfaces doesn´t > give me any way to query the entitystore. So it seem impossible to me to find > the entities I want to change. I´ve tried several approaches, one of which > are casting the StateStore to an EntityStore and then visit all > EntitiesState´s and do some conditionals there. For example: > > private static class MigrateReadableIdentifierOperation implements > MigrationOperation { > ... > @Override > public void upgrade(StateStore stateStore, Migrator migrator) > throws IOException { > Set<EntityState> entitiesToMigrate = new > HashSet<EntityState>(); > EntityStore entityStore = (EntityStore)stateStore; > entityStore.visitEntityStates(new > EntityStore.EntityStateVisitor() { > @Override > public void visitEntityState(EntityState > entityState) { > if(shouldMigrate()) { > > entitiesToMigrate.add(entityState); > } > } > }, /* How do i get the module????*/ ); > > .... Migrate entityStates > } > > } > > The problem here is that I cannot find a way to get a reference to the Module > I´m running in. Since the MigrationOperation isn´t injected it doesn´t seem > like it´s possible to get a reference to any application component. So my > questions are: > > 1. Is using unitOfWork.create(MyEntity.class, "myReadableIdentifier") a good > solution to support my use case? > 2. Is there an easy way to change the identity of an entity that already > exist in the EntityStore? > 3. How do you use the MigrationOperation to update entities when you don´t > know the id of the entities until runtime? Specifically; How do you get > access to application components from an instance of a MigrationOperation? > > > Best regards > Webstep AS > > RONNIE NESSA | Senior Consultant > Mob : +47 970 69 512 | [email protected] > www.webstep.no > > > > > > > > _______________________________________________ > qi4j-dev mailing list > [email protected] > http://lists.ops4j.org/mailman/listinfo/qi4j-dev
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