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RE: [eclipselink-users] Stale Data Between GUIs Using EclipseLink JPA

If you correctly optimize your JPA application, you should not see any major
performance difference to JDBC. In fact if you use caching and other
performance features optimally, you should notice a major performance

Analysis and optimizing performance is never easy, you really need to figure
out where your time is being spent, such as using a performance profiler.

A good place to start is,

There are a large set of performance optimization features in EclipseLink
- Caching
- Parameter binding, statement caching, connection pooling
- Batch writing
- Batch reading, joining
- Read-only queries
- Fetch groups
- Named queries
- Fetch size
- Sequence number preallocation
- Cursors and pagination

MikeyL wrote:
> 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.
> MikeyL 
> -----Original Message-----
> From: eclipselink-users-bounces@xxxxxxxxxxx
> [mailto:eclipselink-users-bounces@xxxxxxxxxxx] On Behalf Of James
> Sutherland
> Sent: Monday, January 12, 2009 10:58 AM
> To: eclipselink-users@xxxxxxxxxxx
> 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.
> MikeyL wrote:
>> 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.
>> MikeyL

--- James Sutherland
 EclipseLink ,
Wiki: EclipseLink , TopLink 
Forums: TopLink , EclipseLink 
Book: Java Persistence 
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