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orphanremoval doesn't delete if add and remove occur without flush

I'm just trying to understand how certain parts of Spring Jpa/Hibernate work. As the title says orphanRemoval only seems to work if entities are flushed to database between adding and removing a child entity from a collection and I'm wondering why.
I've got a parent class with a #OneToMany association with a child class
#Entity
class Parent {
#Id
#GeneratedValue
#Getter
private Long id;
#OneToMany(mappedBy = parent, cascade=ALL, orphanRemoval=true)
#Getter
private Set<Child> children;
public Parent(){
children = new HashSet<Child>();
}
public Child addChild(Child child){
child.setParent(this);
children.add(child);
return child;
}
public void removeChild(Child child){
child.setParent(null);
children.remove(child);
}
}
#Entity
class Child {
#Id
#GeneratedValue
#Getter
private Long id;
#ManyToOne
#Setter
private Parent parent;
}
I was testing to get the child to delete when removed from the parent like so (using an #Autowired JPARepository<Parent,Long> and #JpaTest annotation)
#ExtendWith(SpringExtension.class)
#DataJpaTest
class PersistTest {
#Autowired ParentRepository repo; // JpaRepository<Parent, Long>
#Autowired EntityManager em;
#Test
public void whenChildRemoved_thenChildDeleted(){
Parent parent = new Parent();
Child child = parent.addChild(new Child());
repo.save(parent);
em.flush(); // test fails if removed
parent.removeChild(child);
repo.saveAndFlush(parent);
assertThat(repo.findById(parent.getId()).get().getChildren()).isEmpty();
assertThat(em.find(Child.class, child.getId()).isNull();
}
}
If the entity manager is not flushed between adding the child to the parent and removing it then both assertions fail and when looking at the generated sql there is no DELETE statement made. If the EM is flushed then a DELETE is made and the tests pass.
Basically just wondering if anyone could explain why this is the case and if putting the two operations in separate #Transactional methods would have the same effect.

You expect some transactions being finished or created, but in reality they didn't. That is why you see this behavior.
#DataJpaTest places on every method separate transaction (which will be rolled back anyway by default BTW);
That is why you can use JpaRepository -- it does not create the transaction itself (in the opposite to CrudRepository), but there is underlying one;
If JpaRepository used #Transactional(REQUIRED_NEW), you'd may remove flush;
Answer to your last question. If you put those operations in the separate #Transactional methods, it will work exactly in the same way, because there is underlying transaction in the test created by the #DataJpaTest -- hibernate usually flushes at the very end of the method. You'd have to use #Transactional(REQUIRED_NEW).

#Version annotation causing 'object references an unsaved transient instance - save the transient instance before flushing' exception [duplicate]

I receive following error when I save the object using Hibernate
object references an unsaved transient instance - save the transient instance before flushing

You should include cascade="all" (if using xml) or cascade=CascadeType.ALL (if using annotations) on your collection mapping.
This happens because you have a collection in your entity, and that collection has one or more items which are not present in the database. By specifying the above options you tell hibernate to save them to the database when saving their parent.

I believe this might be just repeat answer, but just to clarify, I got this on a #OneToOne mapping as well as a #OneToMany. In both cases, it was the fact that the Child object I was adding to the Parent wasn't saved in the database yet. So when I added the Child to the Parent, then saved the Parent, Hibernate would toss the "object references an unsaved transient instance - save the transient instance before flushing" message when saving the Parent.
Adding in the cascade = {CascadeType.ALL} on the Parent's reference to the Child solved the problem in both cases. This saved the Child and the Parent.
Sorry for any repeat answers, just wanted to further clarify for folks.
#OneToOne(cascade = {CascadeType.ALL})
#JoinColumn(name = "performancelog_id")
public PerformanceLog getPerformanceLog() {
return performanceLog;
}

Introduction
When using JPA and Hibernate, an entity can be in one of the following 4 states:
New - 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 or Transient state.
To become persisted we need to either explicitly call the persist method or make use of the transitive persistence mechanism.
Persistent - 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).
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.
Removed - Although JPA demands that managed entities only are allowed to be removed, Hibernate can also delete detached entities (but only through a remove method call).
Entity state transitions
To move an entity from one state to the other, you can use the persist, remove or merge methods.
Fixing the problem
The issue you are describing in your question:
object references an unsaved transient instance - save the transient instance before flushing
is caused by associating an entity in the state of New to an entity that's in the state of Managed.
This can happen when you are associating a child entity to a one-to-many collection in the parent entity, and the collection does not cascade the entity state transitions.
So, you can fix this by adding cascade to the entity association that triggered this failure, as follows:
The #OneToOne association
#OneToOne(
mappedBy = "post",
orphanRemoval = true,
cascade = CascadeType.ALL)
private PostDetails details;
Notice the CascadeType.ALL value we added for the cascade attribute.
The #OneToMany association
#OneToMany(
mappedBy = "post",
orphanRemoval = true,
cascade = CascadeType.ALL)
private List<Comment> comments = new ArrayList<>();
Again, the CascadeType.ALL is suitable for the bidirectional #OneToMany associations.
Now, in order for the cascade to work properly in a bidirectional, you also need to make sure that the parent and child associations are in sync.
The #ManyToMany association
#ManyToMany(
mappedBy = "authors",
cascade = {
CascadeType.PERSIST,
CascadeType.MERGE
}
)
private List<Book> books = new ArrayList<>();
In a #ManyToMany association, you cannot use CascadeType.ALL or orphanRemoval as this will propagate the delete entity state transition from one parent to another parent entity.
Therefore, for #ManyToMany associations, you usually cascade the CascadeType.PERSIST or CascadeType.MERGE operations. Alternatively, you can expand that to DETACH or REFRESH.

This happens when saving an object when Hibernate thinks it needs to save an object that is associated with the one you are saving.
I had this problem and did not want to save changes to the referenced object so I wanted the cascade type to be NONE.
The trick is to ensure that the ID and VERSION in the referenced object is set so that Hibernate does not think that the referenced object is a new object that needs saving. This worked for me.
Look through all of the relationships in the class you are saving to work out the associated objects (and the associated objects of the associated objects) and ensure that the ID and VERSION is set in all objects of the object tree.

Or, if you want to use minimal "powers" (e.g. if you don't want a cascade delete) to achieve what you want, use
import org.hibernate.annotations.Cascade;
import org.hibernate.annotations.CascadeType;
...
#Cascade({CascadeType.SAVE_UPDATE})
private Set<Child> children;

In my case it was caused by not having CascadeType on the #ManyToOne side of the bidirectional relationship. To be more precise, I had CascadeType.ALL on #OneToMany side and did not have it on #ManyToOne. Adding CascadeType.ALL to #ManyToOne resolved the issue.
One-to-many side:
#OneToMany(cascade = CascadeType.ALL, mappedBy="globalConfig", orphanRemoval = true)
private Set<GlobalConfigScope>gcScopeSet;
Many-to-one side (caused the problem)
#ManyToOne
#JoinColumn(name="global_config_id")
private GlobalConfig globalConfig;
Many-to-one (fixed by adding CascadeType.PERSIST)
#ManyToOne(cascade = CascadeType.PERSIST)
#JoinColumn(name="global_config_id")
private GlobalConfig globalConfig;

This occurred for me when persisting an entity in which the existing record in the database had a NULL value for the field annotated with #Version (for optimistic locking). Updating the NULL value to 0 in the database corrected this.

This isn't the only reason for the error. I encountered it just now for a typo error in my coding, which I believe, set a value of an entity which was already saved.
X x2 = new X();
x.setXid(memberid); // Error happened here - x was a previous global entity I created earlier
Y.setX(x2);
I spotted the error by finding exactly which variable caused the error (in this case String xid). I used a catch around the whole block of code that saved the entity and printed the traces.
{
code block that performed the operation
} catch (Exception e) {
e.printStackTrace(); // put a break-point here and inspect the 'e'
return ERROR;
}

Don't use Cascade.All until you really have to. Role and Permission have bidirectional manyToMany relation. Then the following code would work fine
Permission p = new Permission();
p.setName("help");
Permission p2 = new Permission();
p2.setName("self_info");
p = (Permission)crudRepository.save(p); // returned p has id filled in.
p2 = (Permission)crudRepository.save(p2); // so does p2.
Role role = new Role();
role.setAvailable(true);
role.setDescription("a test role");
role.setRole("admin");
List<Permission> pList = new ArrayList<Permission>();
pList.add(p);
pList.add(p2);
role.setPermissions(pList);
crudRepository.save(role);
while if the object is just a "new" one, then it would throw the same error.

beside all other good answers, this could happen if you use merge to persist an object and accidentally forget to use merged reference of the object in the parent class. consider the following example
merge(A);
B.setA(A);
persist(B);
In this case, you merge A but forget to use merged object of A. to solve the problem you must rewrite the code like this.
A=merge(A);//difference is here
B.setA(A);
persist(B);

If your collection is nullable just try: object.SetYouColection(null);

This issue happened to me when I created a new entity and an associated entity in a method marked as #Transactional, then performed a query before saving. Ex
#Transactional
public someService() {
Entity someEntity = new Entity();
AssocaiatedEntity associatedEntity = new AssocaitedEntity();
someEntity.setAssociatedEntity(associatedEntity);
associatedEntity.setEntity(someEntity);
// Performing any query was causing hibernate to attempt to persist the new entity. It would then throw an exception
someDao.getSomething();
entityDao.create(someEntity);
}
To fix, I performed the query before creating the new entity.

To add my 2 cents, I got this same issue when I m accidentally sending null as the ID. Below code depicts my scenario (and OP didn't mention any specific scenario).
Employee emp = new Employee();
emp.setDept(new Dept(deptId)); // --> when deptId PKID is null, same error will be thrown
// calls to other setters...
em.persist(emp);
Here I m setting the existing department id to a new employee instance without actually getting the department entity first, as I don't want to another select query to fire.
In some scenarios, deptId PKID is coming as null from calling method and I m getting the same error.
So, watch for null values for PK ID

It can also happen when you are having OneToMany relation and you try to add the child entity to the list in parent entity, then retrieve this list through parent entity (before saving this parent entity), without saving child entity itself, e.g.:
Child childEntity = new Child();
parentEntity.addChild(childEntity);
parentEntity.getChildren(); // I needed the retrieval for logging, but one may need it for other reasons.
parentRepository.save(parentEntity);
The error was thrown when I saved the parent entity. If I removed the retrieval in the previous row, then the error was not thrown, but of course that's not the solution.
The solution was saving the childEntity and adding that saved child entity to the parent entity, like this:
Child childEntity = new Child();
Child savedChildEntity = childRepository.save(childEntity);
parentEntity.addChild(savedChildEntity);
parentEntity.getChildren();
parentRepository.save(parentEntity);

If you're using Spring Data JPA then addition #Transactional annotation to your service implementation would solve the issue.

I also faced the same situation. By setting following annotation above the property made it solve the exception prompted.
The Exception I faced.
Exception in thread "main" java.lang.IllegalStateException: org.hibernate.TransientObjectException: object references an unsaved transient instance - save the transient instance before flushing: com.model.Car_OneToMany
To overcome, the annotation I used.
#OneToMany(cascade = {CascadeType.ALL})
#Column(name = "ListOfCarsDrivenByDriver")
private List<Car_OneToMany> listOfCarsBeingDriven = new ArrayList<Car_OneToMany>();
What made Hibernate throw the exception:
This exception is thrown at your console because the child object I attach to the parent object is not present in the database at that moment.
By providing #OneToMany(cascade = {CascadeType.ALL}) , it tells Hibernate to save them to the database while saving the parent object.

i get this error when i use
getSession().save(object)
but it works with no problem when I use
getSession().saveOrUpdate(object)

For the sake of completeness: A
org.hibernate.TransientPropertyValueException
with message
object references an unsaved transient instance - save the transient instance before flushing
will also occur when you try to persist / merge an entity with a reference to another entity which happens to be detached.

One other possible reason: in my case, I was attempting to save the child before saving the parent, on a brand new entity.
The code was something like this in a User.java model:
this.lastName = lastName;
this.isAdmin = isAdmin;
this.accountStatus = "Active";
this.setNewPassword(password);
this.timeJoin = new Date();
create();
The setNewPassword() method creates a PasswordHistory record and adds it to the history collection in User. Since the create() statement hadn't been executed yet for the parent, it was trying to save to a collection of an entity that hadn't yet been created. All I had to do to fix it was to move the setNewPassword() call after the call to create().
this.lastName = lastName;
this.isAdmin = isAdmin;
this.accountStatus = "Active";
this.timeJoin = new Date();
create();
this.setNewPassword(password);

There is another possibility that can cause this error in hibernate. You may set an unsaved reference of your object A to an attached entity B and want to persist object C. Even in this case, you will get the aforementioned error.

There are so many possibilities of this error some other possibilities are also on add page or edit page. In my case I was trying to save a object AdvanceSalary. The problem is that in edit the AdvanceSalary employee.employee_id is null Because on edit I was not set the employee.employee_id. I have make a hidden field and set it. my code working absolutely fine.
#Entity(name = "ic_advance_salary")
#Table(name = "ic_advance_salary")
public class AdvanceSalary extends BaseDO{
#Id
#GeneratedValue(strategy = GenerationType.IDENTITY)
#Column(name = "id")
private Integer id;
#ManyToOne(fetch = FetchType.EAGER)
#JoinColumn(name = "employee_id", nullable = false)
private Employee employee;
#Column(name = "employee_id", insertable=false, updatable=false)
#NotNull(message="Please enter employee Id")
private Long employee_id;
#Column(name = "advance_date")
#DateTimeFormat(pattern = "dd-MMM-yyyy")
#NotNull(message="Please enter advance date")
private Date advance_date;
#Column(name = "amount")
#NotNull(message="Please enter Paid Amount")
private Double amount;
#Column(name = "cheque_date")
#DateTimeFormat(pattern = "dd-MMM-yyyy")
private Date cheque_date;
#Column(name = "cheque_no")
private String cheque_no;
#Column(name = "remarks")
private String remarks;
public AdvanceSalary() {
}
public AdvanceSalary(Integer advance_salary_id) {
this.id = advance_salary_id;
}
public Integer getId() {
return id;
}
public void setId(Integer id) {
this.id = id;
}
public Employee getEmployee() {
return employee;
}
public void setEmployee(Employee employee) {
this.employee = employee;
}
public Long getEmployee_id() {
return employee_id;
}
public void setEmployee_id(Long employee_id) {
this.employee_id = employee_id;
}
}

I think is because you have try to persist an object that have a reference to another object that is not persist yet, and so it try in the "DB side" to put a reference to a row that not exists

Case 1:
I was getting this exception when I was trying to create a parent and saving that parent reference to its child and then some other DELETE/UPDATE query(JPQL). So I just flush() the newly created entity after creating parent and after creating child using same parent reference. It Worked for me.
Case 2:
Parent class
public class Reference implements Serializable {
#Id
#Column(precision=20, scale=0)
private BigInteger id;
#Temporal(TemporalType.TIMESTAMP)
private Date modifiedOn;
#OneToOne(mappedBy="reference")
private ReferenceAdditionalDetails refAddDetails;
.
.
.
}
Child Class:
public class ReferenceAdditionalDetails implements Serializable{
private static final long serialVersionUID = 1L;
#Id
#OneToOne
#JoinColumn(name="reference",referencedColumnName="id")
private Reference reference;
private String preferedSector1;
private String preferedSector2;
.
.
}
In the above case where parent(Reference) and child(ReferenceAdditionalDetails) having OneToOne relationship and when you try to create Reference entity and then its child(ReferenceAdditionalDetails), it will give you the same exception. So to avoid the exception you have to set null for child class and then create the parent.(Sample Code)
.
.
reference.setRefAddDetails(null);
reference = referenceDao.create(reference);
entityManager.flush();
.
.

In my case , issue was completely different. I have two classes let's say c1 & c2. Between C1 & C2 dependency is OneToMany. Now if i am saving C1 in DB it was throwing above error.
Resolution of this problem was to get first C2's id from consumer request and find C2 via repository call.Afterwards save c2 into C1 object .Now if i am saving C1, it's working fine.

I was facing the same error for all PUT HTTP transactions, after introducing optimistic locking (#Version)
At the time of updating an entity it is mandatory to send id and version of that entity. If any of the entity fields are related to other entities then for that field also we should provide id and version values, without that the JPA try to persist that related entity first as a new entity
Example: we have two entities --> Vehicle(id,Car,version) ; Car(id, version, brand); to update/persist Vehicle entity make sure the Car field in vehicle entity has id and version fields provided

Simple way of solving this issue is save the both entity.
first save the child entity and then save the parent entity.
Because parent entity is depend on child entity for the foreign key value.
Below simple exam of one to one relationship
insert into Department (name, numOfemp, Depno) values (?, ?, ?)
Hibernate: insert into Employee (SSN, dep_Depno, firstName, lastName, middleName, empno) values (?, ?, ?, ?, ?, ?)
Session session=sf.openSession();
session.beginTransaction();
session.save(dep);
session.save(emp);

One possible cause of the error is the inexistence of the setting of the value of the parent entity ; for example for a department-employees relationship you have to write this in order to fix the error :
Department dept = (Department)session.load(Department.class, dept_code); // dept_code is from the jsp form which you get in the controller with #RequestParam String department
employee.setDepartment(dept);

I faced this exception when I did not persist parent object but I was saving the child. To resolve the issue, with in the same session I persisted both the child and parent objects and used CascadeType.ALL on the parent.

My problem was related to #BeforeEach of JUnit. And even if I saved the related entities (in my case #ManyToOne), I got the same error.
The problem is somehow related to the sequence that I have in my parent.
If I assign the value to that attribute, the problem is solved.
Ex.
If I have the entity Question that can have some categories (one or more) and entity Question has a sequence:
#GeneratedValue(strategy = GenerationType.SEQUENCE, generator = "feedbackSeq")
#Id
private Long id;
I have to assign the value question.setId(1L);

Just make Constructor of your mapping in your base class.
Like if you want One-To-One relation in Entity A, Entity B.
if your are taking A as base class, then A must have a Constructor have B as a argument.

Spring Data delete function not deleting records

I have the following simple application
Users Entity
#Entity
public class Users implements Serializable {
#Id
#GeneratedValue
private long id;
private String name;
#OneToMany(mappedBy = "user", fetch = FetchType.EAGER, cascade = {CascadeType.ALL})
private Set<UserRoleUser> userRoleUser;
// GETTERS AND SETTERS
}
UserRole Entity
#Entity
public class UserRole implements Serializable {
#Id
#GeneratedValue
private long id;
private String roleName;
#OneToMany(mappedBy = "userrole", fetch = FetchType.LAZY, cascade = CascadeType.ALL)
private Set<UserRoleUser> userRoleUser;
// GETTERS AND SETTERS
}
UserRoleUser Many to many resolver class
#Entity
public class UserRoleUser implements Serializable {
#Id
#GeneratedValue
private long id;
#ManyToOne
#JoinColumn(name = "fk_userId")
private Users user;
#ManyToOne
#JoinColumn(name = "fk_userroleId")
private UserRole userrole;
// GETTERS AND SETTERS
}
UserRoleUserRepository
#Repository
#Transactional
public interface UserRoleUserRepository extends JpaRepository<UserRoleUser, Long>, QueryDslPredicateExecutor<UserRoleUser>{
}
Main Application class
#SpringBootApplication
#Configuration
public class Application {
public static void main(String[] args) {
ConfigurableApplicationContext context = SpringApplication.run(Application.class, args);
UserRoleUserRepository userRoleUserRepository = context.getBean(UserRoleUserRepository.class);
Iterable<UserRoleUser> findAll = userRoleUserRepository.findAll(QUserRoleUser.userRoleUser.id.gt(0));
for (UserRoleUser userRoleUser : findAll) {
userRoleUserRepository.delete(userRoleUser);
}
}
}
On running the main application, the database records in the UserRoleUser table are not being deleted. What could be the issue? I am using Spring Data and QueryDsl.
I have also tried putting the delete functionality on a Controller but still doesn't work.
#RestController
#RequestMapping("/api")
public class DeleteController {
#Autowired
UserRoleUserRepository userRoleUserRepository;
#GetMapping("/delete")
public String delete() {
Iterable<UserRoleUser> findAll = userRoleUserRepository.findAll(QUserRoleUser.userRoleUser.id.gt(0));
for (UserRoleUser userRoleUser : findAll) {
userRoleUserRepository.delete(userRoleUser);
}
return new Date().toString();
}
}

If you need to use the given methods provided by CrudRepository, use the JpaRepository.deleteInBatch(). This solves the problem.

The problem is the entities are still attached and will not be deleted until they become detached. If you delete by their id instead of the entity itself, it will delete them.
One thing I noticed is you are deleting the users one at a time which could lead to a database performance hit as the query will be recreated each time. The easiest thing to do is to add all the ids to a set then delete the set of ids. Something like this:
Set<Integer> idList = new HashSet<>();
for (UserRoleUser userRoleUser : findAll) {
idList.add(userRoleUser.getId());
}
if (!idList.isEmpty()) {
userRoleUserRepository.delete(idList);
}
then in your repository add the delete method
#Modifying
#Query("DELETE FROM UserRoleUser uru WHERE uru.id in ?1")
#Transactional
void delete(Set<Integer> id);

The reason why the child objects (UserRoleUser) are not being deleted upon userRoleUserRepository.delete(userRoleUser) call is that each UserRoleUser points to a Users which in turn holds a #OneToMany reference Set<UserRoleUser> userRoleUser.
As described in this StackOverflow answer, what your JPA implementation (e.g. Hibernate) effectively does is:
The cache takes note of the requested child exclusion
The cache however does not verify any changes in Set<UserRoleUser>
As the parent #OneToMany field has not been updated, no changes are made
A solution would go through first removing the child element from Set<UserRoleUser> and then proceed to userRoleUserRepository.delete(userRoleUser) or userRepository.save(user)
In order to avoid this complication two answers have been provided:
Remove element by Id, by calling userRoleUserRepository.deleteById(userRoleUser.getId()) : in this case the entity structure (and therefore the parent) is not checked before deletion. In the analog case of deleteAll something more convoluted such as userRoleUserRepository.deleteByIdIn(userRoleUserList.stream().map(UserRoleUser::getId).collect(Collectors.toList())) would have to be employed
Convert your CrudRepository to a JpaRepository and use its deleteInBatch(userRoleUserList) method. As explained in this article and this StackOverflow answer the deleteInBatch method tries to delete all records at once, possibly generating a StackOverflow error in the case the number of records is too large. As repo.deleteAll() removes one record at a time this error it minimizes this risk (unless the call is itself inside a #Transactional method)
According to this StackOverflow answer, extra care should be used when recurring to deleteInBatch as it:
Does not cascade to other entities
Does not update the persistence context, requiring it to be cleared (the method bypasses the cache)
Finally , as far as I know , there is no way this could be done by simply calling userRoleUserRepository.delete(userRoleUser) without first updating the parent object. Any updates on this (whether by allowing such behaviour through annotations, configuration or any other means) would be a welcome addition to the answer.

Hibernate exception when setting the #joinedColumn(table) property to an entity class that extends another entiry class

I have the following scenario:
Entity Command:
#Entity
public class Command {
#Id
#GeneratedValue
private long id;
#Column(nullable=false)
private Date timeOfExecution;
--constructors, getters, setters...--
Entity CmdTest that extends Command:
#Entity
#SecondaryTable(name = "CmdTest")
public class CmdTest extends Command{
#Column(table = "CmdTest", nullable = false)
private String testParam;
#OneToOne
#JoinColumn(table="CmdTest")
private Citizen citizen;
-- getters, setters, construcotr --
}
Entity Citizen:
#Entity
public class Citizen {
#Id
#GeneratedValue
private long id;
#Column(nullable=false)
private String name;
#OneToOne(mappedBy="citizen")
private CmdTest cmdTest;
-- getters, setters, constructor --
}
As you can see, I have a bidirectional relationship between Citizen and CmdTest.
I want to persist citizen first, and then the CmdTest.
I am using a web service to call initTest() method of MyBean. MyBean creates a Citizen and a CmdTest instance and then tries to persist the citizen first, and then the CmdTest.
Here is my initTest() method:
public void initTest() {
CmdTest cmd = new CmdTest();
cmd.setTestParam("asd");
cmd.setTimeOfExecution(new Date());
Citizen citizen = new Citizen();
citizen.setName("John Doe");
citizen.setCmdTest(cmd);
cmd.setCitizen(citizen);
em.persist(citizen);
em.persist(cmd);
}
By setting #JoinColumn(table="CmdTest") on citizen field I try to tell JPA to persist citizen_id foreign key inside CmdTest table, if I comment out that line, everything works fine, but I get citizen_id foreign key inside the Command table.
When I put #JoinColumn(table="CmdTest") I get the following exception: Not-null property references a transient value - transient instance must be saved before current operation
I know I could persist the CmdTest first to put the transient CmdTest object in persistence context, and then the Citizen and it would work. I tried it.
But, I want to know, why is this not working? Is it a bug in Hibernate or JPA? I can't seem to find the reason...

You got this exception because you were trying to save citizen object with a reference to cmd object, while you didn't persisted the cmd instance to the database.
That's how hibernate works, it persisits and manages objects in the database, when it tries to persist the citizen instance it finds that it was mapped to an object (cmd), when it tries to construct this relationship in the db, it will look for the respective cmd object, using id, but it won't find it won't find it that's why you will get the Exception Not-null property references a transient value - transient instance must be saved before current operation as the cmd wasn't persisted.
You need to persist/save the cmd object to DB before trying saving citizen object, this is how should be your code:
public void initTest() {
CmdTest cmd = new CmdTest();
cmd.setTestParam("asd");
cmd.setTimeOfExecution(new Date());
Citizen citizen = new Citizen();
citizen.setName("John Doe");
em.persist(cmd);
citizen.setCmdTest(cmd);
cmd.setCitizen(citizen);
em.persist(citizen);
}
So this isn't a bug in Hibernate, but this is how it's intended to work you can't map an object to another transient (not persisited) one.

JPA - Reload #OneToMany dependencies automatically

I have this scenario:
public abstract class AbstractEntity {
#Id #GeneratedValue(strategy = GenerationType.TABLE)
protected Long id;
}
public class User extends AbstractEntity {
#OneToMany(mappedBy = "user", cascade = CascadeType.ALL)
private Set<Dependent> dependents;
}
public class Dependent extends AbstractEntity {
#ManyToOne
#JoinColumn
private User user;
}
When I try to insert() a new User instance with some Dependent's that already are present in database, what means they have the id field populated, I get a Detached entity passed to persist exception.
It can be solved by manually loading all the Dependents from database, but it don't look right.
I would like to know how to make JPA automatically load them when id field is populated. How can I do that?

If you are using JPA API use:
EntityManager.merge(T t)
instead of
EntityManager.persist(Object object)
Since you are using CascadeType.ALL, when you use merge, the JPA Provider will try to update the Users (in case they exists in database) or will create new ones.
Documentation: http://docs.oracle.com/javaee/6/api/javax/persistence/EntityManager.html.