I have a plain JPA Entity with the ID-Attribute generated:
#Entity(name = "AUTO_COMPLETION")
public class AutoCompletion extends AbstractEntity {
#Id
#GeneratedValue(strategy = GenerationType.SEQUENCE, generator = "aip_seq")
#SequenceGenerator(name = "aip_seq", sequenceName = "aip_seq", allocationSize = 1)
#Column(name = "ID")
private Long id;
...
}
I create an JPA Entity:
AutoCompletion c2a1 = new AutoCompletion();
c2a1.setClient(c2);
c2a1.setText("c2a1");
c2a1.setType(AutoCompletionType.PERSON);
autoCompletionService.create(c1a1);
Create is implemented as follows:
#Override
public T create(final T t) {
this.em.persist(t);
return t;
}
Now the entity gets an written into the database along with the ID-Attribute set. I want to retrieve it again by a function:
List<AutoCompletion> completions = autoCompletionService.getAutoCompletions()
I thought I could call
completions.contains(c2a1)
but it always returns false... I don't understand why. Shouldn't it return true?
I would suggest to implement hashCode and equals
The object you created when you persist and the object retrieved will always not be the equal. Yes they are logically equal since they pertain to the same row in the DB, but they are different object references and point to different locations in memory.
See javadoc for List.contains. It uses equals method of your class to compare. Since you have not overriden the equals method, this will default obj1 == obj2 to operation, which will return true only if they point to the same location in memory.
You would get the same entity instance only if the calls were done in the same transaction. I guess that's not your case, you're calling service classes and you probably don't have a transaction scope bigger than service.
As others have already suggested, equals() an hashcode() need to be implemented in order for List#contains() to work like you expect it. This might or might not have consequences on the rest of your code, it should be analyzed.
Related
Let´s assume these two entities:
#Entity
public class MyEntity {
#Id private String id;
#OneToMany(mappedBy = "myEntity", cascade = ALL) private Set<MyEntityPredecessor> predecessors;
}
#Entity
public class MyEntityPredecessor{
#Id private String id;
#ManyToOne(name = "entityID", nullable = false) private MyEntity myEntity;
#ManyToOne(name = "entityPre", nullable = false) private MyEntity predecessor;
}
When I try to call a delete with Spring Boot Data (JPA) with a MyEntity Instance, it will work some times (I see the select and then the delete statements in correct order), but sometimes it will try to run an update on the second entity trying to set the "entityPre" Field to null (even thoug it is set to nullable=falsE), causing the DB to send an error (null not allowed!! from DB constraint).
Strangely, this will happen at "random" calls to the delete...
I just call "myEntityRepository.getOne(id)", and then myEntityRepository.delete() with the result... There is no data difference in the DB between calls, the data structure has no null values when calling the delete method, so that should not be the reason.
Why is JPA sometimes trying to call updates on the Predecessor Table, and sometimes directly deleting the values? Am I missing something?
Add a similar ManyToOne annotated set to MyEntity which refers to the other non-nullable property, like:
#OneToMany(mappedBy = "predecessor", cascade = ALL) private Set<MyEntityPredecessor> other;
some explanation:
The issue doesn't happen randomly, but happen when you try to delete an entity which is linked to one (or more) MyEntityPredecessor via the predecessor property (which is mapped to the entityPre field)
Only the other field (entityID) is mapped back to the MyEntity object, so the deletion-cascade only happens via by that field.
How can I know if a class is annotated with javax.persistence.Entity?
Person (Entity)
#Entity
#Table(name = "t_person")
public class Person {
...
}
PersonManager
#Stateless
public class PersonManager {
#PersistenceContext
protected EntityManager em;
public Person findById(int id) {
Person person = this.em.find(Person.class, id);
return person;
}
I try to do it with instance of as the following
#Inject
PersonManager manager;
Object o = manager.findById(1);
o instanceof Entity // false
however the result is false, shouldn't it be true?
While the existing answers provide a (somehow) working solution, some things should be noted:
Using an approach based on Reflection implies (a) Performance Overhead and (b) Security Restrictions (see Drawbacks of Reflection).
Using an ORM-specific (here: Hibernate) approach risks portability of the code towards other execution environments, i.e., application containers or other customer-related settings.
Luckily, there is a third JPA-only way of detecting whether a certain Java class (type) is a (managed) #Entity. This approach makes use of standardized access to the javax.persistence.metamodel.MetaModel. With it you get the method
Set < EntityType > getEntities();
It only lists types annotated with #Entity AND which are detected by the current instance of EntityManager you use. With every object of EntityType it is possible to call
Class< ? > getJavaType();
For demonstration purposes, I quickly wrote a method which requires an instance of EntityManager (here: em), either injected or created ad-hoc:
private boolean isEntity(Class<?> clazz) {
boolean foundEntity = false;
Set<EntityType<?>> entities = em.getMetamodel().getEntities();
for(EntityType<?> entityType :entities) {
Class<?> entityClass = entityType.getJavaType();
if(entityClass.equals(clazz)) {
foundEntity = true;
}
}
return foundEntity;
}
You can provide such a method (either public or protected) in a central place (such as a Service class) for easy re-use by your application components. The above example shall just give a direction of what to look for aiming at a pure JPA approach.
For reference see sections 5.1.1 (page 218) and 5.1.2 (page 219f) of the JPA 2.1 specification.
Hope it helps.
If the statement
sessionFactory.getClassMetadata( HibernateProxyHelper.getClassWithoutInitializingProxy( Person.class ) ) != null;
is true, than it is an entity.
#NiVer's answer is valid. But, if you don't have a session or sessionFactory at that point you could use Reflection. Something like:
o.getClass().getAnnotation(Entity.class) != null;
I have an entity service on which I need to filter a collection of child entity, based on a list of id's. My service have a public method which receive the id of the parent entity and a list of id's of some of his children entities.
By default, I know that JPA will fetch all related entities and this his the actual behavior. But we need to work on the performance of the service. So instead of getting all related entities and filter them with many loop (filter on id's and also on other properties like date property), I want to get only entities concerned by my request.
My Parent entity
#Entity
#Table(name = "MyParent")
public class MyParentEntity {
#Id
#GeneratedValue(strategy = GenerationType.SEQUENCE,
generator = "SEQ_MyParent")
#SequenceGenerator(allocationSize = 1, name = "SEQ_MyParent",
sequenceName = "SEQ_MyParent")
#Column(name = "ID_PARENT")
private Long id;
#OneToMany(mappedBy = "myParent", cascade = CascadeType.ALL,
fetch = FetchType.EAGER, orphanRemoval = true)
private final List<MyChildEntity> myChild = new ArrayList<MyChildEntity>();
}
My Child Entity
#Entity
#Table(name = "MyChild")
public class MyChildEntity {
#Id
#GeneratedValue(strategy = GenerationType.SEQUENCE,
generator = "SEQ_MyChild")
#SequenceGenerator(allocationSize = 1, name = "SEQ_MyChild",
sequenceName = "SEQ_MyChild")
#Column(name = "ID_CHILD")
private Long id;
#ManyToOne
#JoinColumn(name = "ID_PARENT")
private MyParentEntity myParent;
}
I'm using Spring-data CrudRepository to get data from my DB and I also extends JpaSpecificationExecutor to use Predicate.
public interface MyParentRepository extends CrudRepository<MyParentEntity, Long>,
JpaSpecificationExecutor<MyParentEntity> {
}
This let me use CrudRepository findOne() method but with a Specification object instead of the regular Long parameter.
Also, I combine multiples Specification's object with the following call:
this.myParentRepository.findOne(Specifications
.where(firstSpecification(parentId))
.and(secondSpecification(childrenIdsList)));
I created a simple junit test with one Parent linked to two children entities. In my request, I'm able to get the parent entity with the provided Id. But even if I provide the child id, I always get both children entities in the list inside the parent.
In my method which return a new Specification object, in which the toPredicate method is override, I'm unable to create a Predicate that will filter my children collection and only get those one I'm interested. I know that the Hibernate Criteria has the possibility to add "Restrictions" but this is not available in the CriteriaBuilder that is provided with the toPredicate method.
public static Specification<MyParentEntite> firstSpecification(final Long id) {
return new Specification<MyParentEntite>() {
#Override
public Predicate toPredicate(Root<MyParentEntite> root,
CriteriaQuery<?> query, CriteriaBuilder cb) {
Predicate predicate = cb.equal(root.get(MyParentEntity_.id), id);
return cb.and(predicate);
}
};
}
public static Specification<MyParentEntite> secondSpecification(final List<Long> ids) {
return new Specification<MyParentEntite>() {
#Override
public Predicate toPredicate(Root<MyParentEntite> root,
CriteriaQuery<?> query, CriteriaBuilder cb) {
Root<MyChildEntity> child = query.from(MyChildEntity.class);
Expression<Long> exp = child.get(MyChildEntity_.id);
Predicate p = exp.in(ids);
return cb.and(p);
}
};
}
In the secondSpecification() method, I also tried to use ListJoin instead of Root directly in the Entity. I searched in other questions here but it seems that this concern is solved with the Hibernate Criteria restrictions or with a LeftJoin, which I tried in my ListJoin in specifing JoinType.LEFT parameter.
Here are links to already tested solutions whitout success :
JPA CriteriaBuilder - How to use "IN" comparison operator
JPA2 Criteria-API: select... in (select from where)
I want to mention that I'm relatively new with Criteria API and Predicate. Maybe I'm missing something that is simple but that is obvious to experienced JPA developpers!
Thanks a lot for your help!
Finally, I found a way to resolved my issue. Requesting only partial collections of sub-entities is something that we found dangerous in terms of data integrity. If a remote service calls to request my parent entity with a partial collection of children's entities within a get, this parent entity object may be return for a modify operation which will result in many "delete" calls on the removed instances of children entities. The persistence API will consider these missing children as relations that were removed, which is something we don't want.
I created a dummy transfert object which contains the partial collections of children's entities requested so this dummy transfert object can't not be use in a future modify operation call. The full version of the parent entity will be used for the "modify" purpose.
Is your JPA provider hibernate?Have you considered the filters in hibernate which can filter the child entities instead of removing them.But the filter usage is somehow very difficult to understand!
the question and problem is pretty simple, though annoying and I am looking for a global solution, because it's application-wide problem for us.
The code below is really not interesting but I post it for clarification!
We use PostgreSQL database with JPA 2.0 and we generated all the facades and entities, of course we did some editing but not much really.
The problem is that every entity contains a Collection of its children, which however (for us only?) is NOT updated after creation a children element.
The objects are written to database, you can select them easily, but what we really would like to see is the refreshed collection of children in parent object.
Why is this happening? If we (manually) refresh the entity of parent em.refresh(parent) it does the trick but it would mean for us a lot of work in Facades I guess. But maybe there is no other way?
Thanks for support!
/* EDIT */
I guess it has to be some annotation problem or cache or something, but I've already tried
#OneToMany(mappedBy = "idquestion", orphanRemoval=true, fetch= FetchType.EAGER)
and
#Cacheable(false)
didn't work properly.
/* EDIT */
Some sample code for understanding.
Database level:
CREATE TABLE Question (
idQuestion SERIAL,
questionContent VARCHAR,
CONSTRAINT Question_idQuestion_PK PRIMARY KEY (idQuestion)
);
CREATE TABLE Answer (
idAnswer SERIAL,
answerContent VARCHAR,
idQuestion INTEGER,
CONSTRAINT Answer_idAnswer_PK PRIMARY KEY (idAnswer),
CONSTRAINT Answer_idQuestion_FK FOREIGN KEY (idQuestion) REFERENCES Question(idQuestion)
);
Than we have generated some Entities in Netbeans 7.1, all of them look similar to:
#Entity
#Table(name = "question", catalog = "jobfairdb", schema = "public")
#XmlRootElement
#NamedQueries({ BLAH BLAH BLAH...})
public class Question implements Serializable {
private static final long serialVersionUID = 1L;
#Id
#Basic(optional = false)
#NotNull
#GeneratedValue(strategy= GenerationType.IDENTITY)
#Column(name = "idquestion", nullable = false)
private Integer idquestion;
#Size(max = 2147483647)
#Column(name = "questioncontent", length = 2147483647)
private String questioncontent;
#OneToMany(mappedBy = "idquestion", orphanRemoval=true)
private Collection<Answer> answerCollection;
Getters... setters...
We use (again) generated facades for them, all implementing AbstractFacade like:
public abstract class CCAbstractFacade<T> {
private Class<T> entityClass;
public CCAbstractFacade(Class<T> entityClass) {
this.entityClass = entityClass;
}
protected abstract EntityManager getEntityManager();
public void create(T entity) {
getEntityManager().persist(entity);
}
The father entity is updated automatically if you use container managed transactions and you fetch the collection after the transaction is complete. Otherwise, you have to update yourself the collection.
This article explains in detail this behaviour: JPA implementation patterns: Bidirectional associations
EDIT:
The simplest way to use Container Managed Transactions is to have transaction-type="JTA" in persistence.xml and use Container-Managed Entity Managers.
You seem to be setting the ManyToOne side, but not adding to the OneToMany, you have to do both.
In JPA, and in Java in general you must update both sides of a bi-directional relationship, otherwise the state of your objects will not be in sync. Not doing so, would be wrong in any Java code, not just JPA.
There is no magic in JPA that will do this for you. EclipseLink does have a magic option for this that you could set through a customizer (mapping.setRelationshipPartnerAttributeName()), but it is not recommended, fixing your code to be correct is the best solution.
See,
http://en.wikibooks.org/wiki/Java_Persistence/Relationships#Object_corruption.2C_one_side_of_the_relationship_is_not_updated_after_updating_the_other_side
I have a very basic relationship between two objects:
#Entity
public class A {
#ManyToOne(optional = false)
#JoinColumn(name="B_ID", insertable=false, updatable=true)
private StatusOfA sa;
getter+setter
}
#Entity
public class StatusOfA {
#Id
private long id;
#Column
private String status;
getter+setter
}
There's only a limited set of StatusOfA in DB.
I perform an update on A in a transaction:
#TransactionalAttribute
public void updateStatusOfA(long id) {
A a = aDao.getAById(123);
if(a != null) {
a.getStatusOfA().getId(); //just to ensure that the object is loaded from DB
StatusOfA anotherStatusOfA = statusOfADao.getStatusOfAById(456);
a.setStatusOfA(aontherStatusOfA);
aDao.saveOrPersistA(a);
}
}
The saveOrPersistA method is here merging 'a'.
I expect Eclipselink to perform only an update on 'a' to update the StatusOfA but it's executing a new insert on StatusOfA table. Oracle is then complaining due to a unique contraint violation (the StatusOfA that Eclipselink tries to persist already exists...).
There is no Cascading here so the problem is not there and Hibernate (in JPA2) is behaving as excepted.
In the same project, I already made some more complex relationships and I'm really surprised to see that the relation here in not working.
Thanks in advance for your help.
What does, statusOfADao.getStatusOfAById() do?
Does it use the same persistence context (same transaction and EntityManager)?
You need to use the same EntityManager, as you should not mix objects from different persistence contexts.
What does saveOrPersistA do exactly? The merge() call should resolve everything correctly, but if you have really messed up objects, it may be difficult to merge everything as you expect.
Are you merging just A, or its status as well? Try also setting the status to the merged result of the status.
Assumptions: #Id#GeneratedValue(strategy = GenerationType.IDENTITY)
Let's consider the following implementations of statusOfADao.getStatusOfAById(456) :
1. returns "proxy" object with just id set:
return new StatusOfA(456);
2. returns entity in new transaction:
EntityManager em = emf.createEntityManager();em.getTransaction().begin();
StatusOfA o = em.find(StatusOfA.class,456);//em.getReference(StatusOfA.class,456);
em.getTransaction().commit();
return o;
3. returns detached entity:
StatusOfA o = em.find(StatusOfA.class,456);//em.getReference(StatusOfA.class,456);
em.detached(o);
return o;
4. returns deserialized-serialized entity:
return ObjectCloner.deepCopy(em.find(StatusOfA.class,456));
5. returns attached entity:
return em.find(StatusOfA.class,456);
Conclusions:
Eclipselink handles only implementation N5 as "expected".
Hibernate handles all five implementations as "expected".
No analisys of what behaviour is jpa spec compliant