Develop Reference

Rolling back a Postgres database using Liquibase in Java

I'm trying to roll back the changes to a postgres table inbetween component tests so each one has a clean db to work with.
I'm using liquibase to set up postgres (the changelog xml to describe the setup and then the liquibase-core Kotlin/Java library to apply it). I'm also using Hibernate to interact with postgres directly. The test framework I'm using is Kotest, using the beforeXXX methods to make sure all the setup happens before the tests run. The database is set up once before everything runs and the idea is to rollback after each test.
From looking in the docs I've found tagDatabase and rollback seem to be what I need, however when running them they don't seem to actually roll anything back.
The code is roughly as follows (this is just test code to see if it works at all, mind - code would ideally be segmented as I descirbed above):
// 1 - (Pre-all-tests) Postgres Setup
liquibase = Liquibase(
"/db/changelog/changelog-master.xml",
ClassLoaderResourceAccessor(),
DatabaseFactory.getInstance().findCorrectDatabaseImplementation(JdbcConnection(connection))
)
liquibase.update(Contexts(), LabelExpression())
liquibase.tag("initialised")
// 2 - Something is inserted
val newEntity = ThingEntity()
entityManager.persist(
entity
)
entityManager.transaction.commit()
entityManager.clear()
// 3 - Cleanup
liquibase.rollback("initialised", Contexts())
// 4 - Fetching
entityManager.find(ThingEntity::class.java, id)
Thing is, after running liquibase.rollback the newEntity I persisted earlier is still present. The tag has dissapeared - if I run the doesTagExist method it returns true and then false after the rollback so the tag is being removed at least.
Given I'm clearing the entity manager after the commit I don't think it's because it's being cached and as I said the tag is being removed - just not the data.
Can anyone tell my why the actual transactions (i.e. the persist) aren't being erased?
Thanks!

Looks like you are using liquibase in a wrong way. What you are trying to have (rollback of data that is added in unit-test) is something close to what is described here: Rollback transaction after #Test
And when you are asking liquibase to rollback to some tag it just executes rollback scripts (if any provided) for changesets that were applied after changeset with tag: https://docs.liquibase.com/commands/community/rollbackbytag.html

Hiberate: can't reload entity from database

I've been struggling for few hours with this one and could do with some help.
A client sends an object that contains a list;
One of the objects in the list has been modified on the client;
In some cases I don't want that modified entity to be persisted to the database, I want to keep the original database values.
I have tried the following and various attempts to clear(), refresh() and flush() the session:
List<Integer> notToModifyIds = dao.getDoNotModifyIds(parentEntity.getId());
MyEntityFromList entityFromClient, entityFromDb;
for(Integer notToModifyId : notToModifyIds){
ListIterator iterator = parentEntity.getEntities().listIterator();
while(iterator.hasNext()){
entityFromClient = (MyEntity) iterator.next();
if(Objects.equals(entityFromClient.getId(), notToModifyId)){
dao.evict(entityFromClient);
entityFromDb = (MyEntity) dao.get(MyEntity.class, notToModifyId);
iterator.remove(entityFromClient);
iterator.add(entityFromDb);
}
}
}
However, no matter what I try I always get the values from the client persisted to the database. When I add a breakpoint after iterator.add() I can check that the database value has not been updated at that point, hence I know that if I could load the entity from the DB then I would have the value I want.
I'm feeling a little suppid!

I don't know if I got the whole scenario here. Are those modified "entitiesFromClient" attached to the Hibernate session? If they are, the changes were probably automatically flushed to the database before you "evicted" them.
Setting a MANUAL flush mode would help you avoid the automatic behaviour.
First of all, I would enable the Hibernate SQL logging to see more precisely what is happening. See Enable Hibernate logging.
Checking the database in another session (while stopped in the breakpoint) will not help if this code is running within a transaction. Even if the change was already flushed in the database you wouldn't see it until the transaction is commited.

Hibernate query returns stale data

I have a hibernate query (hibernate 3) that only reads data from the database. The database is updated by a separate application and the query result does not reflect the changes in the database.
With a bit of research, I think it may have something to do with the Hibernate L2 cache (I don't think it's the L1 cache since I always open a new session and close it after it's done).
Session session = sessionFactoryWrapper.getSession();
List<FlowCount> result = session.createSQLQuery(flowCountSQL).list();
session.close();
I tried disabling the second-layer cache in the hibernate config file but it's not working:
<property name="hibernate.cache.use_second_level_cache">false</property>
<property name="hibernate.cache.use_query_cache">false</property>
<propertyname="cache.provider_class">org.hibernate.cache.NoCacheProvider</property>
I also added session.setCacheMode(CacheMode.Refresh); after Session session = sessionFactoryWrapper.getSession(); to force a refresh on the L1 cache but still not working...
Is there another way to pick up the changes in the database? Am I doing something wrong on how to disable the cache? Thanks.
Update:
I did another experiment by monitoring the database query log:
Run the code the 1st time. Check the log. The query shows up.
Wait a few minutes. The data has changed by another application. I verified it through MySql Workbench. To distinguish from the previous query I add a dummy condition.
Run the code the 2nd time. Check the log and the query shows up.
Both time I'm using the same query but since the data has changed, the result should be different but somehow it's not...

In order to force a L1 cache refresh you can use the refresh(Object) method of Session.
From the Hibernate Docs,
Re-read the state of the given instance from the underlying database.
It is inadvisable to use this to implement long-running sessions that
span many business tasks. This method is, however, useful in certain
special circumstances. For example
where a database trigger alters the object state upon insert or update
after executing direct SQL (eg. a mass update) in the same session
after inserting a Blob or Clob
Moreover you mentioned that you added session.setCacheMode(CacheMode.Refresh) to force a refresh on the L1 cache. This won't work because, CacheMode doesn't have to do anything with L1 cache. From the Hibernate Docs again,
CacheMode controls how the session interacts with the second-level
cache and query cache.

Without second-level cache and query cache, hibernate will always fetch all data from database in a new session.
You can check which query exactly is executed by Hibernate by enabling DEBUG log level for org.hibernate package (and TRACE level for org.hibernate.type if you want to see bound variables).

How old of a change is the query reflecting? If it is showing the changes after sometime, it might have to do with how you obtain your session.
I am not familiar with the SessionFactoryWrapper class, is this a custom class that you wrote? Are you somehow caching the session object longer than it is necessary? If so, the query will be reusing the objects if it has already been loaded in the session. This is the idea behind the repeatable read semantics that Hibernate guarantees.
You can clear the session before running your query and it will then return the latest data.

Hibernate's built-in connection pooling mechanism is bugged.
Replace it with a production quality alternative like c3p0.
I had the exact same issue where stale data was returned until I started using c3p0.

Just in case it IS the 1st Level Cache
Can you show the query you make ?
See following Bugs:
https://hibernate.atlassian.net/browse/HHH-9367
https://jira.grails.org/browse/GRAILS-11645
Additional:
http://howtodoinjava.com/2013/07/01/understanding-hibernate-first-level-cache-with-example/
http://www.dineshonjava.com/p/cacheing-in-hibernate-first-level-and.html#.VhZ7o3VElhE
Repeatable finder problem caused by Hibernates 1st Level Cache
To be clear, both test succeed - not logically at all:
userByEmail('foo#bar.com').email != 'foo#bar.com'
Complete Test
#Issue('https://jira.grails.org/browse/GRAILS-11645')
class FirstLevelCacheSpec extends IntegrationSpec {
def sessionFactory
def setup() {
User.withNewSession {
User user = new User(email: 'test#test.org', password: 'test-password')
user.save(flush: true, failOnError: true)
}
}
private void updateObjectInNewSession(){
User.withNewSession {
def u = User.findByEmail('test#test.org', [cache: false])
u.email = 'foo#bar.com'
u.save(flush: true, failOnError: true)
}
}
private User userByEmail(String email){
User.findByEmail(email, [cache: false])
}
def "test first update"() {
when: 'changing the object in another session'
updateObjectInNewSession()
then: 'retrieving the object by changed identifier (no 2nd level cache)'
userByEmail('foo#bar.com').email == 'foo#bar.com'
}
def "test stale object in 1st level"() {
when: 'changing the object after pulling objects to cache by finder'
userByEmail('test#test.org')
updateObjectInNewSession()
then: 'retrieving the object by changed identifier (no 2nd level cache)'
userByEmail('foo#bar.com').email != 'foo#bar.com'
}
}

Save changes to database vaadin

I have an application which has a table and when you click on an item in the table it fills in a group of textfields with its data (FieldGroup), and then you have the option of saving the changes I was wondering how would I save the changes the user makes to my postgres database. I am using vaadin and hibernate for this application. So far I have tried to do
editorField.commit() // after the user clicks the save button
I have tried
editorField.commit()
hbsession.persist(editorField) //hbsession is the name of my Session
and I have also tried
editorField.commit();
hbsession.save(editorField);
The last two ones give me the following error
Caused by: org.hibernate.SessionException: Session is closed!

Well, the first thing you need to realize is Vaadin differs from conventional request/response web framework. Actually, Vaadin is *event driven* framework very similar to Swing. It builds a application context from very first click of the user and holds it during whole website visit. The problem is there is no entry request point you can start hibernate session and no response point to close. There are tons of requests during a single click on button.
So, entitymanager-per-request pattern is completely useless. It is better to use one standalone em or em-per-session pattern with hibernate.connection_release after_transaction to keep connection pool low.
To the JPAContianer, it is not usable as far you need to refresh the container or you have to handle beans with relations. Also, I did not manage to get it working with batch load, so every reading of entry or relation equals one select to DB. Do not support lazy loading.
All you need is open EM/session. Try to use suggested patters or open EM/session every transaction and merge your bean first.
Your question is quite complex and hard to answer, but I hope these links help you get into:
Pojo binding strategy for hibernate
https://vaadin.com/forum#!/thread/39712
MVP-lite
https://vaadin.com/directory#addon/mvp-lite (stick with event driven pattern)

I have figured out how to make changes to the database here is some code to demonstrate:
try {
/** define the session and begin it **/
hbsession = HibernateUtil.getSessionFactory().getCurrentSession();
hbsession.beginTransaction();
/** table is the name of the Bean class linked to the corresponding SQL table **/
String query = "UPDATE table SET name = " + textfield.getValue();
/** Run the string as an SQL query **/
Query q = hbsession.createQuery(query);
q.executeUpdate(); /** This command saves changes or deletes a entry in table **/
hbsession.getTransaction().commit();
} catch (RuntimeException rex) {
hbsession.getTransaction().rollback();
throw rex;
}

Java SimpleJPA for AWS SimpleDB Select Query

I'm having trouble getting objects back out of SimpleDB using the simpleJPA persistance API. I have successfully installed all the jars and can persist objects no problem. However I cannot seem to retrieve objects using select queries - but weirdly I can get results using count queries. There are no errors or exceptions, the queries simply don't return any results. When I debug I can view the actual AWS Query that is being generated in the background by simpleJPA, and when I run this query against a domain it returns the expected results no problem.
I've included my Java code below, it should return me a list of all the users in my database.
Query query = em.createQuery("SELECT u FROM User u");
List<User> results = (List<User>)query.getResultList();
As I said I can persist objects and count them, so there isn't anything wrong with my entity manager or factory, its just returning empty lists. If you need any more information just ask,
Thanks in advance!

I never got to the bottom of this problem. In the end I started a new AWS project in Eclipse and re-added the JAR files, solving the issue.