This question already has answers here:
Spring Data JPA Update #Query not updating?
(5 answers)
Closed 2 years ago.
The community reviewed whether to reopen this question 1 year ago and left it closed:
Original close reason(s) were not resolved
Let's suppose to have this situation:
We have Spring Data configured in the standard way, there is a Respository object, an Entity object and all works well.
Now for some complex motivations I have to use EntityManager (or JdbcTemplate, whatever is at a lower level than Spring Data) directly to update the table associated to my Entity, with a native SQL query. So, I'm not using Entity object, but simply doing a database update manually on the table I use as entity (it's more correct to say the table from which I get values, see next rows).
The reason is that I had to bind my spring-data Entity to a MySQL view that makes UNION of multiple tables, not directly to the table I need to update.
What happens is:
In a functional test, I call the "manual" update method (on table from which the MySQL view is created) as previously described (through entity-manager) and if I make a simple Respository.findOne(objectId), I get the old object (not updated one). I have to call Entitymanager.refresh(object) to get the updated object.
Why?
Is there a way to "synchronize" (out of the box) objects (or force some refresh) in spring-data? Or am I asking for a miracle?
I'm not ironical, but maybe I'm not so expert, maybe (or probably) is my ignorance. If so please explain me why and (if you want) share some advanced knowledge about this amazing framework.
If I make a simple Respository.findOne(objectId) I get old object (not
updated one). I've to call Entitymanager.refresh(object) to get
updated object.
Why?
The first-level cache is active for the duration of a session. Any object entity previously retrieved in the context of a session will be retrieved from the first-level cache unless there is reason to go back to the database.
Is there a reason to go back to the database after your SQL update? Well, as the book Pro JPA 2 notes (p199) regarding bulk update statements (either via JPQL or SQL):
The first issue for developers to consider when using these [bulk update] statements
is that the persistence context is not updated to reflect the results
of the operation. Bulk operations are issued as SQL against the
database, bypassing the in-memory structures of the persistence
context.
which is what you are seeing. That is why you need to call refresh to force the entity to be reloaded from the database as the persistence context is not aware of any potential modifications.
The book also notes the following about using Native SQL statements (rather than JPQL bulk update):
■ CAUTION Native SQL update and delete operations should not be
executed on tables mapped by an entity. The JP QL operations tell the
provider what cached entity state must be invalidated in order to
remain consistent with the database. Native SQL operations bypass such
checks and can quickly lead to situations where the inmemory cache is
out of date with respect to the database.
Essentially then, should you have a 2nd level cache configured then updating any entity currently in the cache via a native SQL statement is likely to result in stale data in the cache.
In Spring Boot JpaRepository:
If our modifying query changes entities contained in the persistence context, then this context becomes outdated.
In order to fetch the entities from the database with latest record.
Use #Modifying(clearAutomatically = true)
#Modifying annotation has clearAutomatically attribute which defines whether it should clear the underlying persistence context after executing the modifying query.
Example:
#Modifying(clearAutomatically = true)
#Query("UPDATE NetworkEntity n SET n.network_status = :network_status WHERE n.network_id = :network_id")
int expireNetwork(#Param("network_id") Integer network_id, #Param("network_status") String network_status);
Based on the way you described your usage, fetching from the repo should retrieve the updated object without the need to refresh the object as long as the method which used the entity manager to merge has #transactional
here's a sample test
#DirtiesContext(classMode = ClassMode.AFTER_CLASS)
#RunWith(SpringJUnit4ClassRunner.class)
#ContextConfiguration(classes = ApplicationConfig.class)
#EnableJpaRepositories(basePackages = "com.foo")
public class SampleSegmentTest {
#Resource
SampleJpaRepository segmentJpaRepository;
#PersistenceContext
private EntityManager entityManager;
#Transactional
#Test
public void test() {
Segment segment = new Segment();
ReflectionTestUtils.setField(segment, "value", "foo");
ReflectionTestUtils.setField(segment, "description", "bar");
segmentJpaRepository.save(segment);
assertNotNull(segment.getId());
assertEquals("foo", segment.getValue());
assertEquals("bar",segment.getDescription());
ReflectionTestUtils.setField(segment, "value", "foo2");
entityManager.merge(segment);
Segment updatedSegment = segmentJpaRepository.findOne(segment.getId());
assertEquals("foo2", updatedSegment.getValue());
}
}
THe title can't definitely reflect my question, however I don't know how to express. I have a JPA entity (VatOperatorBalance which has a field saleBalance), lets say I retrieve the entity at the first time, and get a entity (VatOperatorBalance#3d6396f5), its saleBalance is 100.0. Now there are other operations which has modified the saleBalance to 200, now I query from database and get a new entity (VatOperatorBalance#10f8ed), sure the saleBalance of this entity is 200.0. However what make me confused it the saleBalance of the old entity (VatOperatorBalance#3d6396f5) is also 200.0.
All these queries and operations are in a single transaction, and the query isn't by EntityManager.find(java.lang.Class<T> entityClass, java.lang.Object primaryKey) which will return entity from cache.
Below is my code
#Rollback(true)
#Test
public void testSale_SingleBet_OK() throws Exception {
// prepare request ...
// query the VatOperatorBalance first
VatOperatorBalance oldBalance = this.getVatOperatorBalanceDao().findByOperator("OPERATOR-111");
//this.entityManager.detach(oldBalance);
logger.debug("------ oldBalance(" + oldBalance + ").");
// the operation which will modify the oldBalance
Context saleReqCtx = this.getDefaultContext(TransactionType.SELL_TICKET.getRequestType(),
clientTicket);
saleReqCtx.setGameTypeId(GameType.VAT.getType() + "");
Context saleRespCtx = doPost(this.mockRequest(saleReqCtx));
RaffleTicket respTicket = (RaffleTicket) saleRespCtx.getModel();
this.entityManager.flush();
this.entityManager.clear();
// assert vat sale balance
VatOperatorBalance newBalance = this.getVatOperatorBalanceDao().findByOperator("OPERATOR-111");
logger.debug("------ newBalance(" + newBalance + ").");
assertEquals(oldBalance.getSaleBalance().add(respTicket.getTotalAmount()).doubleValue(), newBalance
.getSaleBalance().doubleValue(), 0);
}
This testcase will fail, I don't understand why this will happen. JPA entity manager will update all entities of same entity type? The oldBalance entity and newBlance entity have same entityId, however they are different Java instance, what happened in JPA entity manager? If I detach the oldBalance entity from EntityManager, testcase will pass.
Note: my test is using Spring4.0.5 and JPA2.1
#piet.t since the entityManager would recognize it is the same entity by its primary key (feel free to try it). So all changes made to this entity through the same entityManager will all affect the same java instance
So in a entity manager, a given entity type with given primary key, there should be only one java instance or managed entity(if query from entity manager, no matter what query criteria, by id or not, the same java instance(managed entity) will be returned).
However in my test case, the entity 'oldBalance' will be updated by "the operation which will modify the oldBalance", and then the call of entityManager.clear() will detach all entities managed by this entity manager, that says 'oldBalance' is detached too.
And the 'newBalance' is managed entity then, that is why they have different java instance identifier. If 'oldBalance' is managed, for example by call entityManager.merge(), it will be the same instance of 'newBalance'.
I think most of your confusion does arise from the flush()-call in your code.
Calling flush will always store the changed value to the database - that's the whoe point of calling flush. When using transactions the changed value might still not be visible via other connections due to the databases transaction machanism but your entityManager will only see the changed value.
Without the clear-call your query - even though it is not using find - would still return the same instance that was previously created (VatOperatorBalance#3d6396f5) since the entityManager would recognize it is the same entity by its primary key (feel free to try it). So all changes made to this entity through the same entityManager will all affect the same java instance while modifications through another entity manager will most likely cause an exception because the entity was update from another transaction.
Some queries might cause an implicit flush, since the cached changes might influence the query-result, so all changes have to be written to the database before executing the query to get a correct result-set.
I hope that does help a bit.
I have a object A which maps to table A in DB
class A {
Integer id;
String field2,field2;field3 ,... fieldN;
//lots of other attribute
}
Now i want to write a DAO api that just updates a single field.One approach is that i can first load the object then changes the attribute i need and then use merge api
//start transcation
A a = session.load(A.class, id);
A.setfieldP(newValue)
session.merge(A)
//commit transcation
Now if i use following code
//start transcation
A a = new A();
a.setId(id); //set a id by which object A exists in DB
A.setfieldP(newValue)
session.merge(A)
//commit transaction
Now second approach all fields except id and fieldP are set to null
1)Now is there any other approach?
2)Can i use update instead of merge ?
If you need to update lots of entities at once the most efficient way is to use a query:
Query query = session.createQuery("update EntityName set fieldP = 'newValue' "
+ "where id IN (75, 76)");
query.executeUpdate();
This allows you to change field values without loading the entity or entities into memory.
It is best practice is to use named queries and named parameters - the above implementation is just an example.
I usually prefer session.get vs session.load, as session.get will return null as opposed to throwing an exception, but it depends on the behavior you want.
loading the object, setting your field, and calling either
session.merge(myObject)
is the standard way, although you can also use
session.saveOrUpdate(myObject)
as long as the object hasn't been detached, which in your case, it won't have been detached. Here is a good article explaining the differences in merge and saveOrUpdate.
In your second example, you are editing the primary key of the object? This is generally bad form, you should delete and insert instead of changing the primary key.
Using JPA you can do it this way.
CriteriaBuilder builder = session.getCriteriaBuilder();
CriteriaUpdate<User> criteria = builder.createCriteriaUpdate(User.class);
Root<User> root = criteria.from(User.class);
criteria.set(root.get("fname"), user.getName());
criteria.set(root.get("lname"), user.getlastName());
criteria.where(builder.equal(root.get("id"), user.getId()));
session.createQuery(criteria).executeUpdate();
One more optimization here could be using dynamic-update set to true for the entity. This will make sure that whenever there is an update, only field(s) which are changed only gets updated.
I learnt Hibernate and used it to reduce my Java code to a vast extent and also able
to reduce the time spent for DB's. Now what type of query should i use to finish my
operations for getting a DB list to be displayed, to update and delete.
My code for deletion is
String newToken = "DELETEUSER";
if(!TokenManager.checkRoleToken(newToken)){
return;
}
Session session = Main.getSession(); //calling the main method to get sesion
Leavetable table = new Leavetable; // intialisation of object table
try{
Transaction tr = session.beginTransaction();
table = session.createQuery();
session.delete(table); // deletion of the object and its properties from selected leaveID
tr.commit();
}
finally{
session.close();
}
My code for Db updation
public void updateLeaveTable( Leavetable leave ) {
String newToken = "ADDUSER";
if( !TokenManager.checkRoleToken( newToken ) ) {
return;
}
Session session = Main.getSession(); // calling the main method to get
// session
try {
session = Main.getSession();
Transaction tr = session.beginTransaction();
session.saveOrUpdate( leave ); // here without query the table gets
// updated How?
tr.commit();
}
finally {
session.close();
}
}
What type of query should I follow. My final task before going into project. When I
know this will start my life as a developer. Any suggestions Please.
Do you mean a HQL query? Well, a typical query on your Leavetable entity would looks like this:
Query q = session.createQuery("from Leavetable t where t.someField = :value");
q.setParameter("value", foo);
List<Leavetable> results = q.list();
However, if you just want to retrieve an entity by identifier, see Session#load() or Session#get(). I don't want to make things too much confusing but while both methods are similar, there is an important difference between both of them. Quoting the Hibernate Forums:
Retrieving objects by identifier
The following Hibernate code snippet
retrieves a User object from the
database:
User user = (User) session.get(User.class, userID);
The get() method is special because
the identifier uniquely identifies a
single instance of a class. Hence it’s
common for applications to use the
identifier as a convenient handle to a
persistent object. Retrieval by
identifier can use the cache when
retrieving an object, avoiding a
database hit if the object is already
cached. Hibernate also provides a
load() method:
User user = (User) session.load(User.class, userID);
The load() method is older; get() was
added to Hibernate’s API due to user
request. The difference is trivial:
If load() can’t find the object in
the cache or database, an exception is
thrown. The load() method never
returns null. The get() method
returns null if the object can’t be
found.
The load() method may return a proxy
instead of a real persistent instance.
A proxy is a placeholder that triggers
the loading of the real object when
it’s accessed for the first time; we
discuss proxies later in this section.
On the other hand, get() never
returns a proxy.
Choosing between get() and load()
is easy: If you’re certain the
persistent object exists, and
nonexistence would be considered
exceptional, load() is a good
option. If you aren’t certain there is
a persistent instance with the given
identifier, use get() and test the
return value to see if it’s null.
Using load() has a further
implication: The application may
retrieve a valid reference (a proxy)
to a persistent instance without
hitting the database to retrieve its
persistent state. So load() might
not throw an exception when it doesn’t
find the persistent object in the
cache or database; the exception would
be thrown later, when the proxy is
accessed.
Of course, retrieving an object by
identifier isn’t as flexible as using
arbitrary queries.
See also the Hibernate Documentation (links below).
Reference
Hibernate Core Reference Guide
10.3. Loading an object
Chapter 14. HQL: The Hibernate Query Language
I have a situation in which I need to re-attach detached objects to a hibernate session, although an object of the same identity MAY already exist in the session, which will cause errors.
Right now, I can do one of two things.
getHibernateTemplate().update( obj )
This works if and only if an object doesn't already exist in the hibernate session. Exceptions are thrown stating an object with the given identifier already exists in the session when I need it later.
getHibernateTemplate().merge( obj )
This works if and only if an object exists in the hibernate session. Exceptions are thrown when I need the object to be in a session later if I use this.
Given these two scenarios, how can I generically attach sessions to objects? I don't want to use exceptions to control the flow of this problem's solution, as there must be a more elegant solution...
So it seems that there is no way to reattach a stale detached entity in JPA.
merge() will push the stale state to the DB,
and overwrite any intervening updates.
refresh() cannot be called on a detached entity.
lock() cannot be called on a detached entity,
and even if it could, and it did reattach the entity,
calling 'lock' with argument 'LockMode.NONE'
implying that you are locking, but not locking,
is the most counterintuitive piece of API design I've ever seen.
So you are stuck.
There's an detach() method, but no attach() or reattach().
An obvious step in the object lifecycle is not available to you.
Judging by the number of similar questions about JPA,
it seems that even if JPA does claim to have a coherent model,
it most certainly does not match the mental model of most programmers,
who have been cursed to waste many hours trying understand
how to get JPA to do the simplest things, and end up with cache
management code all over their applications.
It seems the only way to do it is discard your stale detached entity
and do a find query with the same id, that will hit the L2 or the DB.
Mik
All of these answers miss an important distinction. update() is used to (re)attach your object graph to a Session. The objects you pass it are the ones that are made managed.
merge() is actually not a (re)attachment API. Notice merge() has a return value? That's because it returns you the managed graph, which may not be the graph you passed it. merge() is a JPA API and its behavior is governed by the JPA spec. If the object you pass in to merge() is already managed (already associated with the Session) then that's the graph Hibernate works with; the object passed in is the same object returned from merge(). If, however, the object you pass into merge() is detached, Hibernate creates a new object graph that is managed and it copies the state from your detached graph onto the new managed graph. Again, this is all dictated and governed by the JPA spec.
In terms of a generic strategy for "make sure this entity is managed, or make it managed", it kind of depends on if you want to account for not-yet-inserted data as well. Assuming you do, use something like
if ( session.contains( myEntity ) ) {
// nothing to do... myEntity is already associated with the session
}
else {
session.saveOrUpdate( myEntity );
}
Notice I used saveOrUpdate() rather than update(). If you do not want not-yet-inserted data handled here, use update() instead...
Entity states
JPA defines the following entity states:
New (Transient)
A newly created object that hasn’t ever been associated with a Hibernate Session (a.k.a Persistence Context) and is not mapped to any database table row is considered to be in the New (Transient) state.
To become persisted we need to either explicitly call the EntityManager#persist method or make use of the transitive persistence mechanism.
Persistent (Managed)
A persistent entity has been associated with a database table row and it’s being managed by the currently running Persistence Context. Any change made to such an entity is going to be detected and propagated to the database (during the Session flush-time).
With Hibernate, we no longer have to execute INSERT/UPDATE/DELETE statements. Hibernate employs a transactional write-behind working style and changes are synchronized at the very last responsible moment, during the current Session flush-time.
Detached
Once the currently running Persistence Context is closed all the previously managed entities become detached. Successive changes will no longer be tracked and no automatic database synchronization is going to happen.
Entity state transitions
You can change the entity state using various methods defined by the EntityManager interface.
To understand the JPA entity state transitions better, consider the following diagram:
When using JPA, to reassociate a detached entity to an active EntityManager, you can use the merge operation.
When using the native Hibernate API, apart from merge, you can reattach a detached entity to an active Hibernate Sessionusing the update methods, as demonstrated by the following diagram:
Merging a detached entity
The merge is going to copy the detached entity state (source) to a managed entity instance (destination).
Consider we have persisted the following Book entity, and now the entity is detached as the EntityManager that was used to persist the entity got closed:
Book _book = doInJPA(entityManager -> {
Book book = new Book()
.setIsbn("978-9730228236")
.setTitle("High-Performance Java Persistence")
.setAuthor("Vlad Mihalcea");
entityManager.persist(book);
return book;
});
While the entity is in the detached state, we modify it as follows:
_book.setTitle(
"High-Performance Java Persistence, 2nd edition"
);
Now, we want to propagate the changes to the database, so we can call the merge method:
doInJPA(entityManager -> {
Book book = entityManager.merge(_book);
LOGGER.info("Merging the Book entity");
assertFalse(book == _book);
});
And Hibernate is going to execute the following SQL statements:
SELECT
b.id,
b.author AS author2_0_,
b.isbn AS isbn3_0_,
b.title AS title4_0_
FROM
book b
WHERE
b.id = 1
-- Merging the Book entity
UPDATE
book
SET
author = 'Vlad Mihalcea',
isbn = '978-9730228236',
title = 'High-Performance Java Persistence, 2nd edition'
WHERE
id = 1
If the merging entity has no equivalent in the current EntityManager, a fresh entity snapshot will be fetched from the database.
Once there is a managed entity, JPA copies the state of the detached entity onto the one that is currently managed, and during the Persistence Context flush, an UPDATE will be generated if the dirty checking mechanism finds that the managed entity has changed.
So, when using merge, the detached object instance will continue to remain detached even after the merge operation.
Reattaching a detached entity
Hibernate, but not JPA supports reattaching through the update method.
A Hibernate Session can only associate one entity object for a given database row. This is because the Persistence Context acts as an in-memory cache (first level cache) and only one value (entity) is associated with a given key (entity type and database identifier).
An entity can be reattached only if there is no other JVM object (matching the same database row) already associated with the current Hibernate Session.
Considering we have persisted the Book entity and that we modified it when the Book entity was in the detached state:
Book _book = doInJPA(entityManager -> {
Book book = new Book()
.setIsbn("978-9730228236")
.setTitle("High-Performance Java Persistence")
.setAuthor("Vlad Mihalcea");
entityManager.persist(book);
return book;
});
_book.setTitle(
"High-Performance Java Persistence, 2nd edition"
);
We can reattach the detached entity like this:
doInJPA(entityManager -> {
Session session = entityManager.unwrap(Session.class);
session.update(_book);
LOGGER.info("Updating the Book entity");
});
And Hibernate will execute the following SQL statement:
-- Updating the Book entity
UPDATE
book
SET
author = 'Vlad Mihalcea',
isbn = '978-9730228236',
title = 'High-Performance Java Persistence, 2nd edition'
WHERE
id = 1
The update method requires you to unwrap the EntityManager to a Hibernate Session.
Unlike merge, the provided detached entity is going to be reassociated with the current Persistence Context and an UPDATE is scheduled during flush whether the entity has modified or not.
To prevent this, you can use the #SelectBeforeUpdate Hibernate annotation which will trigger a SELECT statement that fetched loaded state which is then used by the dirty checking mechanism.
#Entity(name = "Book")
#Table(name = "book")
#SelectBeforeUpdate
public class Book {
//Code omitted for brevity
}
Beware of the NonUniqueObjectException
One problem that can occur with update is if the Persistence Context already contains an entity reference with the same id and of the same type as in the following example:
Book _book = doInJPA(entityManager -> {
Book book = new Book()
.setIsbn("978-9730228236")
.setTitle("High-Performance Java Persistence")
.setAuthor("Vlad Mihalcea");
Session session = entityManager.unwrap(Session.class);
session.saveOrUpdate(book);
return book;
});
_book.setTitle(
"High-Performance Java Persistence, 2nd edition"
);
try {
doInJPA(entityManager -> {
Book book = entityManager.find(
Book.class,
_book.getId()
);
Session session = entityManager.unwrap(Session.class);
session.saveOrUpdate(_book);
});
} catch (NonUniqueObjectException e) {
LOGGER.error(
"The Persistence Context cannot hold " +
"two representations of the same entity",
e
);
}
Now, when executing the test case above, Hibernate is going to throw a NonUniqueObjectException because the second EntityManager already contains a Book entity with the same identifier as the one we pass to update, and the Persistence Context cannot hold two representations of the same entity.
org.hibernate.NonUniqueObjectException:
A different object with the same identifier value was already associated with the session : [com.vladmihalcea.book.hpjp.hibernate.pc.Book#1]
at org.hibernate.engine.internal.StatefulPersistenceContext.checkUniqueness(StatefulPersistenceContext.java:651)
at org.hibernate.event.internal.DefaultSaveOrUpdateEventListener.performUpdate(DefaultSaveOrUpdateEventListener.java:284)
at org.hibernate.event.internal.DefaultSaveOrUpdateEventListener.entityIsDetached(DefaultSaveOrUpdateEventListener.java:227)
at org.hibernate.event.internal.DefaultSaveOrUpdateEventListener.performSaveOrUpdate(DefaultSaveOrUpdateEventListener.java:92)
at org.hibernate.event.internal.DefaultSaveOrUpdateEventListener.onSaveOrUpdate(DefaultSaveOrUpdateEventListener.java:73)
at org.hibernate.internal.SessionImpl.fireSaveOrUpdate(SessionImpl.java:682)
at org.hibernate.internal.SessionImpl.saveOrUpdate(SessionImpl.java:674)
Conclusion
The merge method is to be preferred if you are using optimistic locking as it allows you to prevent lost updates.
The update is good for batch updates as it can prevent the additional SELECT statement generated by the merge operation, therefore reducing the batch update execution time.
Undiplomatic answer: You're probably looking for an extended persistence context. This is one of the main reasons behind the Seam Framework... If you're struggling to use Hibernate in Spring in particular, check out this piece of Seam's docs.
Diplomatic answer: This is described in the Hibernate docs. If you need more clarification, have a look at Section 9.3.2 of Java Persistence with Hibernate called "Working with Detached Objects." I'd strongly recommend you get this book if you're doing anything more than CRUD with Hibernate.
If you are sure that your entity has not been modified (or if you agree any modification will be lost), then you may reattach it to the session with lock.
session.lock(entity, LockMode.NONE);
It will lock nothing, but it will get the entity from the session cache or (if not found there) read it from the DB.
It's very useful to prevent LazyInitException when you are navigating relations from an "old" (from the HttpSession for example) entities. You first "re-attach" the entity.
Using get may also work, except when you get inheritance mapped (which will already throw an exception on the getId()).
entity = session.get(entity.getClass(), entity.getId());
I went back to the JavaDoc for org.hibernate.Session and found the following:
Transient instances may be made persistent by calling save(), persist() or
saveOrUpdate(). Persistent instances may be made transient by calling delete(). Any instance returned by a get() or load() method is persistent. Detached instances may be made persistent by calling update(), saveOrUpdate(), lock() or replicate(). The state of a transient or detached instance may also be made persistent as a new persistent instance by calling merge().
Thus update(), saveOrUpdate(), lock(), replicate() and merge() are the candidate options.
update(): Will throw an exception if there is a persistent instance with the same identifier.
saveOrUpdate(): Either save or update
lock(): Deprecated
replicate(): Persist the state of the given detached instance, reusing the current identifier value.
merge(): Returns a persistent object with the same identifier. The given instance does not become associated with the session.
Hence, lock() should not be used straightway and based on the functional requirement one or more of them can be chosen.
I did it that way in C# with NHibernate, but it should work the same way in Java:
public virtual void Attach()
{
if (!HibernateSessionManager.Instance.GetSession().Contains(this))
{
ISession session = HibernateSessionManager.Instance.GetSession();
using (ITransaction t = session.BeginTransaction())
{
session.Lock(this, NHibernate.LockMode.None);
t.Commit();
}
}
}
First Lock was called on every object because Contains was always false. The problem is that NHibernate compares objects by database id and type. Contains uses the equals method, which compares by reference if it's not overwritten. With that equals method it works without any Exceptions:
public override bool Equals(object obj)
{
if (this == obj) {
return true;
}
if (GetType() != obj.GetType()) {
return false;
}
if (Id != ((BaseObject)obj).Id)
{
return false;
}
return true;
}
Session.contains(Object obj) checks the reference and will not detect a different instance that represents the same row and is already attached to it.
Here my generic solution for Entities with an identifier property.
public static void update(final Session session, final Object entity)
{
// if the given instance is in session, nothing to do
if (session.contains(entity))
return;
// check if there is already a different attached instance representing the same row
final ClassMetadata classMetadata = session.getSessionFactory().getClassMetadata(entity.getClass());
final Serializable identifier = classMetadata.getIdentifier(entity, (SessionImplementor) session);
final Object sessionEntity = session.load(entity.getClass(), identifier);
// override changes, last call to update wins
if (sessionEntity != null)
session.evict(sessionEntity);
session.update(entity);
}
This is one of the few aspects of .Net EntityFramework I like, the different attach options regarding changed entities and their properties.
I came up with a solution to "refresh" an object from the persistence store that will account for other objects which may already be attached to the session:
public void refreshDetached(T entity, Long id)
{
// Check for any OTHER instances already attached to the session since
// refresh will not work if there are any.
T attached = (T) session.load(getPersistentClass(), id);
if (attached != entity)
{
session.evict(attached);
session.lock(entity, LockMode.NONE);
}
session.refresh(entity);
}
Sorry, cannot seem to add comments (yet?).
Using Hibernate 3.5.0-Final
Whereas the Session#lock method this deprecated, the javadoc does suggest using Session#buildLockRequest(LockOptions)#lock(entity)and if you make sure your associations have cascade=lock, the lazy-loading isn't an issue either.
So, my attach method looks a bit like
MyEntity attach(MyEntity entity) {
if(getSession().contains(entity)) return entity;
getSession().buildLockRequest(LockOptions.NONE).lock(entity);
return entity;
Initial tests suggest it works a treat.
Perhaps it behaves slightly different on Eclipselink. To re-attach detached objects without getting stale data, I usually do:
Object obj = em.find(obj.getClass(), id);
and as an optional a second step (to get caches invalidated):
em.refresh(obj)
try getHibernateTemplate().replicate(entity,ReplicationMode.LATEST_VERSION)
In the original post, there are two methods, update(obj) and merge(obj) that are mentioned to work, but in opposite circumstances. If this is really true, then why not test to see if the object is already in the session first, and then call update(obj) if it is, otherwise call merge(obj).
The test for existence in the session is session.contains(obj). Therefore, I would think the following pseudo-code would work:
if (session.contains(obj))
{
session.update(obj);
}
else
{
session.merge(obj);
}
to reattach this object, you must use merge();
this methode accept in parameter your entity detached and return an entity will be attached and reloaded from Database.
Example :
Lot objAttach = em.merge(oldObjDetached);
objAttach.setEtat(...);
em.persist(objAttach);
calling first merge() (to update persistent instance), then lock(LockMode.NONE) (to attach the current instance, not the one returned by merge()) seems to work for some use cases.
Property hibernate.allow_refresh_detached_entity did the trick for me. But it is a general rule, so it is not very suitable if you want to do it only in some cases. I hope it helps.
Tested on Hibernate 5.4.9
SessionFactoryOptionsBuilder
try getHibernateTemplate().saveOrUpdate()