> but it seems to do that on every call to ObjectContext.commit()! We can clean up this code a bit to make sure custom strategies are not themselves responsible for synchronization of the call and ensuring a single invocation. Though if you extend from BaseSchemaUpdateStrategy or use one of the built-in strategies (like SchemaUpdateStrategyFactory) you shouldn't worry about this at all. Cayenne will do the right thing.
There's a small overhead in invoking this code in BaseSchemaUpdateStrategy: if (!run && (inProgress == null || !inProgress)) ... But really not that much. Andrus > On Oct 12, 2017, at 9:38 PM, Dirk Lattermann <dl...@alqualonde.de> wrote: > > I experimented a bit with the SchemaUpdateStrategyFactory to create a > test SchemaUpdateStrategy. It is correct that Cayenne calls the > strategy before any app code can access the DB, but it seems to do that > on every call to ObjectContext.commit()! That's quite surprising to me > because I think it would be sufficient to call it only before the first > database access of a DataNode. If the Strategy is quite expensive (for > example, using Liquibase), then that has quite a performance impact. > > Is it possibly considered the task of the Factory to return a strategy > only on the first call to the DataNode? That also would be quite > surprising to me, but I did not find any documentation about that. > > > Am Mon, 9 Oct 2017 09:29:22 +0300 > schrieb Andrus Adamchik <and...@objectstyle.org>: > >> Hi Dirk, >> >> When using explicit transactions [1], the connection is always the >> same within the transaction. "runtime.performInTransaction(..)" [2] >> can also take TransactionListener as a second argument that you may >> implement to set connection properties. >> >> Unrelated to the above, specifically for schema generation purposes >> you can bind SchemaUpdateStrategyFactory [3] when you start your >> runtime, that creates SchemaUpdateStrategy (either one of the >> standard choices like CreateIfNoSchemaStrategy, or your custom >> version). Cayenne is guaranteed to invoke the strategy before any of >> the app code can access the DB. >> >> Hopefully it will point you in the right direction. >> >> Andrus >> >> [1] >> http://cayenne.apache.org/docs/4.0/cayenne-guide/persistent-objects-objectcontext.html#transactions >> [2] >> https://cayenne.apache.org/docs/4.0/api/index.html?org/apache/cayenne/configuration/server/ServerRuntime.html >> [3] >> https://cayenne.apache.org/docs/4.0/api/org/apache/cayenne/access/dbsync/SchemaUpdateStrategyFactory.html >> >> >>> On Oct 8, 2017, at 12:39 PM, Dirk Lattermann <dl...@alqualonde.de> >>> wrote: >>> >>> Hello, >>> >>> is it possible to control which database connection is used when >>> committing an ObjectContext? >>> >>> For example, when using an explicit transaction, the database >>> connection used in the thread starting the exception must always be >>> the same. >>> >>> Now, I have a use case where I want to obtain a PostgresQL advisory >>> exclusive session lock and do some DDL to create a db schema. Then I >>> want to write something into that schema using Cayenne, and after >>> that, release the lock. That's to somewhat atomically initialize a >>> db schema. >>> >>> For normal schema usage, I want to obtain an advisory shared lock >>> in the db connection and use that connection with Cayenne. >>> >>> That mechanism can also be used to manipulate portions of the >>> database that must be done without concurrent access. >>> >>> It's how I solved the problem with Hibernate, where a Hibernate >>> session represents a JDBC Connection. It is bound to the current >>> thread and used for all Hibernate DB accesses during the session. >>> That worked quite well. >>> >>> Would it be possible to do something similar with Cayenne? >> >
