RE: [eclipselink-users] Stale Data Between GUIs Using EclipseLink JPA
Usually ORM solutions can be faster. Quite a bit of your poor performance may be related to you getting and releasing an EntityManager per database operation. This is a classic "anti" pattern that is discussed in a hibernate FAQ.
Also, realize that one reason an SQL solution may be faster too is that you currently have a contrived flat object representation. When moving to more complex objects, the required SQL becomes more difficult to write and things like Lazy fetch and fetch groups really start to shine in both development cost and performance. Finally, I would add that you really only need to perform good enough. If the eclipselink solution is taking say 100ms to do something versus 10ms, if it isn't performance critical, err on the side of ease of development Using a JPA solution you can do post development profiling and thunk to native SQL where necessary reducing bother code complexity and the amount of classes you need.
From: eclipselink-users-bounces@xxxxxxxxxxx [mailto:eclipselink-users-bounces@xxxxxxxxxxx] On Behalf Of Liford, Michael W.
Sent: Monday, January 12, 2009 11:59 AM
To: EclipseLink User Discussions
Subject: RE: [eclipselink-users] Stale Data Between GUIs Using EclipseLink JPA
Thanks for the reply, James.
I read a message in a newsgroup that recommended getting a new EntityManager for every database operation and closing it right after the operation. I also surrounded any updates, inserts, and deletes with transactions and commits. Seems to work now.
I am rather disappointed in the performance of EclipseLink. I have another version of the same application using native SQL (ResultSet, PreparedStatement, etc.). It is much faster. EclipseLink makes the coding easier, but there is a price to pay.
[mailto:eclipselink-users-bounces@xxxxxxxxxxx] On Behalf Of James Sutherland
Sent: Monday, January 12, 2009 10:58 AM
Subject: Re: [eclipselink-users] Stale Data Between GUIs Using EclipseLink JPA
In JPA an EntityManager represents an extended persistence context, in that any object read into the EntityManager will remain until you either
close() or clear() the EntityManager. You can also call refresh() on an object to refresh it explicitly. An EntityManager normally relates to a single transaction or request. So to see changes made in another EntityManager, or another machine, you need to either create a new EntityManager, or clear() the existing one, or refresh() each object you want refreshed.
EclipseLink also managed a 2nd level shared cache at the EntityManagerFactory level. This cache also caches the objects that are read, so if you want fresh data you must also ensure this cache is refreshed. Calling refresh() will also refresh the cache (unless you have flushed changes), the cache also has invalidation API and configuration, or can be disabled using persistence.xml "eclipselink.cache.shared.default"="false", or the @Cache annotation or orm.xml.
I would recommend you continue working with JPA, and not use the native API or Mapping Workbench.
> I am playing with a Movie-Actor application to learn about
> persistence. I have a Derby database with a Movies table with title,
> rating, release year, etc., and an Actors table with name, birth date,
> etc. I have an associative table joining a many-to-many relationship
> between Movies and Actors. The associative table declares foreign key
> fields with references back to the parent tables. I designed Swing
> GUIs to display the data. The Movie GUI will display actors for a
> selected movie in a child table. The Actor GUI will display movies for
> a selected actor in a child table. The Entity Manager Factory and
> Entity Manager are instantiated once by the main GUI at program start.
> The Movie and Actor DAOs get the Entity Manager from the main screen.
> The problem is that changes made in one GUIs do not get reflected in
> the other. E.g., if I add the movie 2 Days in the Valley to actress
> Charlize Theron in the Actor GUI then click on 2 Days in the Valley in
> the Movie GUI, Charlize is not listed as an actor in the child table.
> Even pressing the Refresh button to reload the Movie table does not
help. How do I synchronize the data between the two GUIs?
> In an attempt to solve the above problem, I took a look at EclipseLink
> Sessions. It seems that I could have the main GUI invoke a server
> session and have separate client sessions for the Movie and Actor
> GUIs. However, when using Workbench to create entity source files from
> my database tables the many-to-many relationship is not picked up by
> Workbench although the foreign key reference constraints are on the
> associative table. I crawled all over the User's Guide and can't find
> how to manually define these relationships in the mapping XML file. Is
this a bug in Workbench?
> Any help and thoughts will be appreciated.
http://wiki.eclipse.org/User:James.sutherland.oracle.com James Sutherland http://www.eclipse.org/eclipselink/
EclipseLink , http://www.oracle.com/technology/products/ias/toplink/
Wiki: http://wiki.eclipse.org/EclipseLink EclipseLink , http://wiki.oracle.com/page/TopLink TopLink
Forums: http://forums.oracle.com/forums/forum.jspa?forumID=48 TopLink , http://www.nabble.com/EclipseLink-f26430.html EclipseLink
Book: http://en.wikibooks.org/wiki/Java_Persistence Java Persistence
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