Michael,
Thanks for your quick answer.
This leads me to two new points:
- You said that an entity is attached when freshly loaded, but I found no
way to explicitly detach entities. Am I right?
If so, I think you should update the documentation which is quite confusing
on this point, and explain clearly that detach entities should be used in a
"write-only" mode.
- Moreover, I think there could be some confusing side effects if entities
always use read-through :
Does this work with a cache or do the entities always read through the
database?
How would this example behave with two different clients :
A client X does the following (let's say title property is indexed):
1. Movie retrievedMovie = movieRepository.findByPropertyValue("Babel");
2. output(retrievedMovie.getTitle()) // prepare some output like Web page
3. ... do some other operations
4. output(retrievedMovie.getTitle()) // for some reason, a second output is
needed
In the same time, a client Y executes the following code:
1. Movie retrievedMovie = movieRepository.findByPropertyValue("Babel");
2.retrievedMovie.setTitle("New title"));
3. retrievedMovie.persist();
4. Some other stuff we don't care
Which should be the value of the movie title for client X on step 4?
Thanks by advance for your answer.
Michel
> Date: Tue, 23 Aug 2011 11:42:13 +0200
> From: Michael Hunger <michael.hun...@neotechnology.com>
> Subject: Re: [Neo4j] [Spring Data Graph] Precisions about Detached
> Entities and SDG under the hood
> To: Neo4j user discussions <user@lists.neo4j.org>
> Message-ID: <3a2f0a73-6183-4b32-a02a-7219f0a7f...@neotechnology.com
> >
> Content-Type: text/plain; charset=us-ascii
>
> there are two states attached and detached:
>
> an entity is detached when it is created or when it is changed outside of a
> transaction.
>
> Otherwise (when it is freshly loaded, or after persist it is attached).
>
> For detached entities: persist() writes the changed properties and
> relationships to the graph. if attached (and inside of a tx) all changes are
> written directly.
>
> In your example you just overwrote the title with Babel and persisted that
> information to the graph, so the assert should say:
> The retrieved movie is attached, it is never detached, so it always refers
> to the node in the graph (read-through) (the data is _not_ copied).
>
> > assertEquals("Babel", retrievedMovie.getTitle());
>
>
> Attached entities read their data directly from the underlying node.
>
> HTH
>
> Michael
>
> The model is different to hibernate, as hibernate has no read-through. We
> would have loved not to support detached entities but as they are so common
> in web-frameworks we had to.
>
> The best way of working with SDG is to use domain level service methods
> which are transactional and do the interaction with the graph. Detached
> entities should just be used to (if at all) to persist
> user input (form data) from the UI.
>
>
>
> Am 23.08.2011 um 10:56 schrieb Michel Domenjoud:
>
> > Hello,
> > I'm currently testing some of Spring Data Graph features, and I have a
> few
> > questions about some usages.
> >
> > Could someone explain to me how the following example works?
> > I run the following unit test:
> >
> > @Test
> > public void testUpdatingEntitiesNotInTransaction(){
> > Movie m = new Movie();
> > m.setTitle("Leon");
> > m.persist();
> > Long id = m.getNodeId();
> > Movie retrievedMovie = movieRepository.findOne(id);
> > m.setTitle("Babel");
> > m.persist();
> > assertEquals("Leon", retrievedMovie.getTitle());
> >
> > }
> >
> > And the assertion at the end fails, as retrievedMovie.getTitle() equals
> > "Babel" and not "Leon".
> > This point is not really clear in the documentation :
> > Does this occurs because of some cache? If so, is it the Neo4j cache? And
> > what is exactly its scope : thread, session, ...?
> > Or is any call to getters triggering an access to the database because of
> > AspectJ?
> >
> > Anyway, unless I misundestood something, it's a bit confusing. Especially
> > when used to APIs like Hibernate, which don't make any refresh of
> retrieved
> > entities once we are outside of a transaction.
> >
> > When I read this in documentation, I don't expect that any persist
> operation
> > affect other retrieved entities :
> > Changing an attached entity inside a transaction will immediately write
> > through the changes to the datastore. Whenever an entity is changed
> outside
> > of a transaction it becomes detached. The changes are stored in the
> entity
> > itself until the next call to persist().
> >
> > All entities returned by library functions are initially in an attached
> > state. Just as with any other entity, changing them outside of a
> transaction
> > detaches them, and they must be reattached with persist() for the data to
> be
> > saved.
> > Maybe I have to precise some points :
> >
> > - I'm using Embedded database, with beforeTest cleaning
> > - I don't use any transaction in this test.
> >
> >
> > Thanks by advance for your help!
> > Michel
> > _______________________________________________
> > Neo4j mailing list
> > User@lists.neo4j.org
> > https://lists.neo4j.org/mailman/listinfo/user
>
_______________________________________________
Neo4j mailing list
User@lists.neo4j.org
https://lists.neo4j.org/mailman/listinfo/user
