Hibernate FetchType.LAZY problem

the_thunderbird · **Joined:** Sat May 12, 2007 3:10 am **Posts:** 8

Hi,

I'm having a problem using FetchType.LAZY on hibernate 3.x where it does not call the database every time I want to use a OneToMany collection...

Here is an example:

class MyRoutine
{
...
@OneToMany
private List<MyRoutineStep> steps;

...

}

When I update a step, and call getSteps() on MyRoutine it retrieves the data lazily as it is supposed to. However when I update it again and then call getSteps it returns the old data and refuses to return the current data unless I reload the whole context...

I have noticed that during refreshes the database is not used...

Any ideas?

farzad · **Posted:** Sun Feb 17, 2008 2:52 pm

How is the second update done?

Farzad-

the_thunderbird · **Joined:** Sat May 12, 2007 3:10 am **Posts:** 8

farzad wrote:

How is the second update done?

Farzad-

There is no second update... Basically I update an entity, let's say I change some text, then save my object back to the database. I then run a query to retrieve an object with the onetomany relationship with the object I just saved.

When I run getSteps on that object it returns what seams to be a cached PersistentBag of step objects, rather than fetching them from the database...

schauder · **Joined:** Thu Jul 05, 2007 9:38 am **Posts:** 287

Is the second select in a different session? Make sure the transaction of that session startet after the commit of the first session/transaction

the_thunderbird · **Joined:** Sat May 12, 2007 3:10 am **Posts:** 8

schauder wrote:

Is the second select in a different session? Make sure the transaction of that session startet after the commit of the first session/transaction

To be honest, I thought it would all be in the same session. If I save the routine object (basically that has the relationship) and refresh the page I'm displaying it on, it updates.

Code:

<bean id="entityManagerFactory" class="org.springframework.orm.jpa.LocalContainerEntityManagerFactoryBean">
      <property name="dataSource" ref="dataSource" />
      <property name="jpaVendorAdapter">
         <bean class="org.springframework.orm.jpa.vendor.HibernateJpaVendorAdapter">
            <property name="database" value="POSTGRESQL" />
            <property name="showSql" value="true" />
            <property name="generateDdl" value="true"/>
            <property name="databasePlatform" value="org.hibernate.dialect.PostgreSQLDialect"/>
         </bean>
      </property>
      <property name="jpaProperties">
         <props>
            <prop key="hibernate.cache.use_query_cache">false</prop>
         </props>
      </property>
   </bean>

Now I am saving the step through my admin interface, when I refresh the routine (routine being the object containing a list of steps) it shows happily (although I'm not doing anything to the routine object, but rather using DWR to retrieve steps, so that the page doesn't refresh).

All DAO's are application beans, which means that they should all be in the same hibernate session?

The problem is when I run: getSteps() it uses a cache and does not call the database, unless it is the first time it runs. The only way I've worked around it, is by manually querying the database and returning a list of steps based on the routine currently being displayed on the page.

As far as I am concerned, hibernate should query the database every time I run myroutine.getSteps(); as it is pointless if it will only reflect the changes when I reload the whole context and it runs it's query for the first and only time...

So in point form:

1. In admin using the same DAO beans, I modify the text of a step and save.
2. I can see the changes in the database and in the list of steps as it's retrieved using javascript and dwr (and not getSteps()) on the routine.
3. When I go to the publicly available page and view said routine, the method getSteps() does not even call the database, but returns a PersistentBag from the first time it was run, rather than actually call the database for updates.

Is there a way to force it to use the database every time I run getSteps()?

schauder · **Joined:** Thu Jul 05, 2007 9:38 am **Posts:** 287

I think you have two options:

Either implement getSteps using some kind of query instead of a mapped multivalue attribute.

Or (and I'd recommend that) reload your object in a new Session().

It makes perfectly sense for Hibernate to use the values it retrieved the very first time.
a) this way it guaranties consistency. Even the simplest loop over your steps can become very difficult when everytime you call getSteps() it would possibly return a different result.

b) It would be a performance nightmare.

Jens

the_thunderbird · **Joined:** Sat May 12, 2007 3:10 am **Posts:** 8

schauder wrote:

I think you have two options:

Either implement getSteps using some kind of query instead of a mapped multivalue attribute.

Or (and I'd recommend that) reload your object in a new Session().

It makes perfectly sense for Hibernate to use the values it retrieved the very first time.
a) this way it guaranties consistency. Even the simplest loop over your steps can become very difficult when everytime you call getSteps() it would possibly return a different result.

b) It would be a performance nightmare.

Jens

I can understand the performance gains, although in theory if you are worried about performance you would actually switch the cache on. This is what is baffling me, I don't want a cache for what I'm doing, and have had to work around it...

However if you are using the same session in theory it should update the step object and it should then easily reflect the changes in getSteps as the object is persistent...

Oh well, I guess I have a work around for now anyhow.

the_thunderbird · **Joined:** Sat May 12, 2007 3:10 am **Posts:** 8

the_thunderbird wrote:

schauder wrote:

I think you have two options:

Either implement getSteps using some kind of query instead of a mapped multivalue attribute.

Or (and I'd recommend that) reload your object in a new Session().

It makes perfectly sense for Hibernate to use the values it retrieved the very first time.
a) this way it guaranties consistency. Even the simplest loop over your steps can become very difficult when everytime you call getSteps() it would possibly return a different result.

b) It would be a performance nightmare.

Jens

I can understand the performance gains, although in theory if you are worried about performance you would actually switch the cache on. This is what is baffling me, I don't want a cache for what I'm doing, and have had to work around it...

However if you are using the same session in theory it should update the step object and it should then easily reflect the changes in getSteps as the object is persistent...

Oh well, I guess I have a work around for now anyhow.

Actually thinking about it... You're right...

getSteps should only use the values it retrieved the first time round, if I'm calling it from an object already fetched from the database. However it should not use those results if I actually query for a new copy of the object which contains getSteps, as the way it works now is making it inconsistent...

I can update the routine and see the changes on the page immediately, but if I update a step even the modified routine still returns an old PersistentBag from when getSteps was first called on a totally different object in the java sense.

the_thunderbird · **Joined:** Sat May 12, 2007 3:10 am **Posts:** 8

the_thunderbird wrote:

schauder wrote:

I think you have two options:

Either implement getSteps using some kind of query instead of a mapped multivalue attribute.

Or (and I'd recommend that) reload your object in a new Session().

It makes perfectly sense for Hibernate to use the values it retrieved the very first time.
a) this way it guaranties consistency. Even the simplest loop over your steps can become very difficult when everytime you call getSteps() it would possibly return a different result.

b) It would be a performance nightmare.

Jens

I can understand the performance gains, although in theory if you are worried about performance you would actually switch the cache on. This is what is baffling me, I don't want a cache for what I'm doing, and have had to work around it...

However if you are using the same session in theory it should update the step object and it should then easily reflect the changes in getSteps as the object is persistent...

Oh well, I guess I have a work around for now anyhow.

Actually thinking about it... You're right...

getSteps should only use the values it retrieved the first time round, if I'm calling it from an object already fetched from the database. However it should not use those results if I actually query for a new copy of the object which contains getSteps, as the way it works now is making it inconsistent...

I can update the routine and see the changes on the page immediately, but if I update a step even the modified routine still returns an old PersistentBag from when getSteps was first called on a totally different object in the java sense.

the_thunderbird · **Joined:** Sat May 12, 2007 3:10 am **Posts:** 8

schauder wrote:

I think you have two options:

Either implement getSteps using some kind of query instead of a mapped multivalue attribute.

Or (and I'd recommend that) reload your object in a new Session().

It makes perfectly sense for Hibernate to use the values it retrieved the very first time.
a) this way it guaranties consistency. Even the simplest loop over your steps can become very difficult when everytime you call getSteps() it would possibly return a different result.

b) It would be a performance nightmare.

Jens

I can understand the performance gains, although in theory if you are worried about performance you would actually switch the cache on. This is what is baffling me, I don't want a cache for what I'm doing, and have had to work around it...

However if you are using the same session in theory it should update the step object and it should then easily reflect the changes in getSteps as the object is persistent...

Oh well, I guess I have a work around for now anyhow.[/quote]

Actually thinking about it... You're right...

getSteps should only use the values it retrieved the first time round, if I'm calling it from an object already fetched from the database. However it should not use those results if I actually query for a new copy of the object which contains getSteps, as the way it works now is making it inconsistent...

I can update the routine and see the changes on the page immediately, but if I update a step even the modified routine still returns an old PersistentBag from when getSteps was first called on a totally different object in the java sense.

schauder · **Joined:** Thu Jul 05, 2007 9:38 am **Posts:** 287

the_thunderbird wrote:

I don't want a cache for what I'm doing

Well the session by definition is a cache, so if you don't want cached objects, close the session and open a new one

the_thunderbird · **Joined:** Sat May 12, 2007 3:10 am **Posts:** 8

schauder wrote:

the_thunderbird wrote:

I don't want a cache for what I'm doing

Well the session by definition is a cache, so if you don't want cached objects, close the session and open a new one

Surely though a single session would update the changes I make to the object (which should be reflected in getSteps())?

Babysittah · **Joined:** Thu Nov 29, 2007 4:11 am **Posts:** 2

The same problem as yours, gotta work it out

schauder · **Joined:** Thu Jul 05, 2007 9:38 am **Posts:** 287

the_thunderbird wrote:

Surely though a single session would update the changes I make to the object (which should be reflected in getSteps())?

Actually: no. Hibernate doesn't update your objects.

Say you have a class A containing a collection of Bs.

you now delete one of Bs (b) by calling session.delete(b);

The collection in A will still contain the b probably causing problems sooner or later.

Of course if A has a simple attribute 'name' and you call setName("someName"); and persist/update it your object reflects the current state of affairs.

Back to the problem at hand: I don't really understand what you are doing (to many Steps involved :).

Can you please show some code what you are actually doing?

jaypee18 · **Posted:** Wed Feb 20, 2008 8:23 pm

the_thunderbird wrote:

schauder wrote:

I

Is there a way to force it to use the database every time I run getSteps()?

You could just call Session.refresh(myRoutine) to force the data to be re-read from the database? Or use Session.evict(step) for all the steps you don't want to be cached in the session?