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From "Hawley, Dan" <dan.haw...@lmco.com>
Subject Issues with Record Locking
Date Tue, 01 Sep 2009 14:36:14 GMT

I seem to need some help understanding how record locking works in Derby because I can't seem
to make it work for me.

I have a single table with about 5,000 records.  There is an Ocean field that has one of two
values: ATL or PAC.  I want the users to be able to query the table using the Ocean attribute
and obtain a lock on all of the "ATL" records from the time the select statement is issued
until they end their editing session and finally update the database.  The lock could be need
for several hours.

I am using Derby in network server mode on my local machine.  I am using JPA to access the
database.  I am using Hibernate Persistence as my JPA provider.  In the persistence.xml file
I set the following property:

<property name = "hibernate.dialect" value="org.hibernate.dialect.DerbyDialect" />
<property name = "hibernate.connection.isolation" value="4" />

When I start the session, it appears that a repeatable read connection is made to the database.

There is an index created on the ocean field in the class using JPA with hibernate extensions:

@Column(name = "OCEAN", nullable = "false");
@org.hibernate.annotations.Index(name = "ocean", columNames="OCEAN"))

I issue the following select statement to retrieve the records from the database and hopefully
obtain the lock:

Public ArrayList<FleetExchangeActivity> getActivities(Ocean ocean, boolean isReadOnly){
  Query q = this.getEntityManager().createQuery("select a from FleetExchangeActivity a where
a.ocean = :ocean").setHint("org.hibernate.readOnly", isReadOnly);
q.setParameter("ocean", ocean);
return (ArrayList<FleetExchangeActivity>) q.getResultList();


I use the isReadOnly boolean to indicate whether the user wishes to view ( no lock) or edit
(lock please) the result set.

I am missing something here?  When I run a test and query all the records with ocean=ATL,
then run the same query again, using the same EntityManager object and the same ocean attribute,
I am able to update the records returned by the second query.

Any help you can provide will be greatly appreciated.  Thanks, Dan

Dan Hawley
Lockheed-Martin Space Systems Company, Sunnyvale, CA
Business Application Programmer, Sr. Staff
Program Plans and Requirements O/B31S
B/181 Col 1A3
Office: (408) 742-3888

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