I want a many-to-many relationship between an entity table and a join table. Invoices consist of a set of subscriptions. A subscription can be a part of multiple invoices (e.g. monthly subscription). Subscriptions consist of a user and a service. I am already using the subscriptions table as a join table for the many-to-many relationship between users and services (e.g. a user can subscribe to multiple services and a single service has multiple users). I have a table, "invoice_subscription," with IDs for both the invoice and subscription. Every table has its own ID. Below is the relevant snippet in the invoice object:
#ManyToMany
#JoinTable(
name = "invoice_subscription",
joinColumns = #JoinColumn(name = "invoice_id"),
inverseJoinColumns = #JoinColumn(name = "subscription_id")
)
public Set<Subscription> getSubscriptions() {
return subscriptions;
}
I am using the following in the subscription object:
#ManyToMany(mappedBy = "subscriptions")
public Set<Invoice> getInvoices() {
return invoices;
}
For the above, I am receiving the error below:
org.hibernate.MappingException: Foreign key (FKfe5yu82iapjynsdyfitclkri4:invoice_subscription [subscription_id])) must have same number of columns as the referenced primary key (subscription [user_id,service_id])
When I switch to two "#JoinColumn" annotations with the IDs in the error, I get the following error:
org.hibernate.AnnotationException: A Foreign key refering com.example.model.Subscription from com.example.model.Invoice has the wrong number of column. should be 1
I agree with this, but it seems to contradict the previous error. I've read documentation, guides, and other questions, but I have not found any useful information. I'm clearly missing something obvious.
I am a newbie to Java Persistence API and Hibernate and using Spring JPA repositories for querying in DB. Now I have two entities in Parent <-> Child relationship with Parent entity with #OneToMany and Child entity with #ManyToOne mapping.
Parent Entity:-
#Entity
#Table(name = "PERSONS")
public class Persons {
...
#OneToMany(mappedBy = "person", cascade = CascadeType.ALL, fetch = FetchType.LAZY, orphanRemoval = true)
public List<Cards> cards = new ArrayList<Cards>();
...
}
Child Entity:-
#Entity
#Table(name = "CARDS")
public class Cards {
...
#ToString.Exclude
#ManyToOne(fetch = FetchType.LAZY)
#JoinColumn(name = "PERSON_ID", nullable = false, insertable = false, updatable = false)
public Person person;
...
}
And I am using my PersonsRepository like below :-
#Repository
public interface PersonsRepository extends JpaRepository<Persons, String> {
....
}
Now the fetchType being used in the relationship is LAZY at both the ends. Now whenever I tried to loop over a List and tried to process the cards for each using person.getCards(), it gives me below error:-
org.hibernate.LazyInitializationException: failed to lazily initialize a collection of role: com.xxx.abc.Persons.cards, could not initialize proxy - no Session
at org.hibernate.collection.internal.AbstractPersistentCollection.throwLazyInitializationException(AbstractPersistentCollection.java:606)
at org.hibernate.collection.internal.AbstractPersistentCollection.withTemporarySessionIfNeeded(AbstractPersistentCollection.java:218)
at org.hibernate.collection.internal.AbstractPersistentCollection.initialize(AbstractPersistentCollection.java:585)
at org.hibernate.collection.internal.AbstractPersistentCollection.read(AbstractPersistentCollection.java:149)
at org.hibernate.collection.internal.PersistentSet.iterator(PersistentSet.java:188)
at java.util.Spliterators$IteratorSpliterator.estimateSize(Spliterators.java:1821)
at java.util.Spliterator.getExactSizeIfKnown(Spliterator.java:408)
at java.util.stream.AbstractPipeline.copyInto(AbstractPipeline.java:481)
at java.util.stream.AbstractPipeline.wrapAndCopyInto(AbstractPipeline.java:472)
at java.util.stream.ReduceOps$ReduceOp.evaluateSequential(ReduceOps.java:708)
at java.util.stream.AbstractPipeline.evaluate(AbstractPipeline.java:234)
at java.util.stream.ReferencePipeline.collect(ReferencePipeline.java:499)
Now I have found everyone saying that using LAZY is the best approach in Hibernate and it says lot more about the correct design of code as well. I agree the way I have used person.getCards() will not have any open session and that is the reason it is giving me LazyInitializationException but the intent behind this is to save a lot more DB calls.
Assuming I have 1000 persons list, that means I have to make 1000 separate calls to getCards() for each person. That's why if I use the FETCHTYPE.EAGER in Person #OneToMany, what is the performance impact since everything will be fetched eagerly.
Need suggestions about the best practices followed for such kind of problems. TIA.
Edit:-
I have a method in service class where I am using #transactional for that like below:-
#Transactional(readOnly = true)
public void fetchData(Integer param1, Timestamp param2, Timestamp param3, List<String> param4, NavigableMap<Long, List<Cards>> param5) {
List<Persons> validPersons = personRepo.getCardsPerPerson(param2, param3);
if(validPersons != null && !validPersons.isEmpty()) {
// store the cards on the basis of epoch timestamp
prepareTimestampVsCardsMap(validPersons, param4, param5);
}
}
private void prepareTimestampVsCardsMap(List<Persons> validPersons, List<String> uList, NavigableMap<Long, List<Cards>> timestampVsCardsList) {
for(Person person : validPersons) {
Long epoch = order.getOrderTime().getTime();
Set<Cards> cardsPerPerson = person.getCards();
}
}
Also, the query being used in repository for getting the cards associated to a person is using join fetch as below:-
#Query(value = "select p from Person p join fetch Cards c on p.id = c.id WHERE p.orderTime BETWEEN ?1 AND ?2 ORDER BY orderTime ASC")
public List<Person> getCardsPerPerson(Timestamp param1, Timestamp param2);
I am still getting the same above mentioned LazyInitializationException. Can anyone please help.
First of all, it's always better to use FetchType.LAZY instead of FetchType.EAGER. Why? Because you might not need all the data every time. If you want to return a list of Persons and display them somehow, somewhere, do you need to fetch all of their cards as well? If not, then FetchType.LAZY would be the better option, and you would then control how much data you need.
LazyInitializationException usually indicates that you didn't fetch all the data you need while your Session was opened. There are many ways to fetch associated data (none of which is keeping the Session opened while processing request):
1. using join fetch in your JPQL/HQL
#Query("select p from Person p join fetch p.cards where ...")
List<Person> getCardsPerPerson(Timestamp param1, Timestamp param2);
2. if you're using Spring Data, you could use #EntityGraph instead of join fetch
#EntityGraph(attributePaths = { "cards" })
List<Person> getPersons();
That way, every time you call getPersons, it will fetch cards as well. Of course, you couldn't use this one if you have to write #Query.
If you're using Spring Data's naming conventions for some simple queries, then #EntityGraph would be an option for fetching associations.
3. using Criteria API
Again, if you're using Spring Data, this is just a fallback solution in case you end up with MultipleBagFetchException. I will not go into details for this one, but in case you encounter this exception, you'll find solution in Vlad Mihalcea's blog post The best way to fix the Hibernate MultipleBagFetchException.
You are under the misconception that EAGER loading means Hibernate will fetch all data with one statement, this is false. With EAGER as a strategy, the framework will just do every query required to fetch all data for every entity.
Example: If one entity has 2 EAGER relationships, fetching one will result in 3 statements, one to load the entity, one for each of its relationships. If you have 3 entities, you will have 7 statements, the initial statement loading the 3 objects, plus 2 per object.
When your treatment requires everything, there is no real performance impact at the moment. But most applications are not made of one treatment. This means every treatment in your application will load everything which is EAGER, even if not needed. This will effectively slow everything down. You also risk loading all your database in memory if everything is in EAGER.
This is why LAZY is the recommended approach.
As for your LazyInitializationException, it seems in your stack trace that you are using the stream API. It's a wild guess due to missing details, but JPA/Hibernate doesn't handle sharing a session between threads, so if you are using parrallelStream it could cause the problem.
I have two tables students and subjects. A student can have more than one subject and vice versa. I have two model classes and vave joined using Many to Many relationship in spring boot and JPA.My problem is how I can delete values from my join table. But I can't figure out how I can do delete from join table. For Student and Subject Model I delete comfortably using deleteById() function.This is my code:
#ManyToMany
#JoinTable(
name = "student_subject",
joinColumns = #JoinColumn(name = "student_id"),
inverseJoinColumns = #JoinColumn(name = "subject_id"))
private Set<SubjectModel> subjects;
//and my repository Class
#Repository
public interface SubjectDao extends JpaRepository<SubjectModel, Integer> {}
You have to delete the corresponding objects form both sides of the link, and then save them.
myStudent.getSubjects().remove(mySubject);
mySubject.getStudents().remove(myStudent);
SubjectDao subjectDao = new SubjectDao();
subjectDao.save(mySubject);
Here another examle: Hibernate: delete many-to-many association
You have two table Student and Subject.
And I suppose you want is delete one of the subject from a student.
For that you should let jpa delete the row from subject and student-subject association table. And dont need to user SubjectRepository.
Take a look.
Student firstStudent=studentRepository.findById(1);
Set<SubjectModel> subs=firstStudent.getSubject();
subs.clear();
firstStudent.setSubject(subs);
studentRepository.save(firstStudent); // this method will delete the row from assiciation table as well as the subject table.
Given this two entities:
post post_category
- id - post_id
- title - name
- text
I'd like to make this query using jpa criteria query:
select * from post
where post.id in (
select post_id from post_category
where name = '<category1>' and name = '<category2>' ... and name = '<categoryN>')
Looking at your query sketch I think it will not return any results. I have changed it to mean name in ('<category1>','<category2>', ...) instead. Which may not match your case.
This assumes that you have your mapping set up properly on your classes for JPA to work. For example
class PostCategory {
private String name;
private Post post;
...
#ManyToOne
public Post getPost() {
return post;
}
...
In which case your DAO code would resemble this (given a List nameValues object)
// Set up the subquery
DetachedCriteria dc = DetachedCriteria.forClass(PostCategory.class)
.setProjection(Projections.property("post.id"))
.add(Restrictions.in("name", nameValues));
Criteria crit = session.createCriteria(Post.class)
.add(Subqueries.eqProperty("id", dc));
But if you want a list of Post objects which have ALL of the categories then you will need to make a separate DetachedCriteria instance for each category and add each as an AND'ed Subquery.
I currently have problems with the JPA at the play framework 1.2.4.
I need to have a UserOptions model in a separate database and want to join it lazyly cause its only needed in one query.
In this query I want to load the options eagerly and by searching I found out that can only be done by using a join query.
If I use eager instead oder lazy, everything would be fine by using User.findById() and the options and the user is found in one query.
But play sends two queries when I use a 'left join fetch' query. So heres the query:
User.find("
SELECT
user
FROM
User user
LEFT JOIN FETCH
user.options options
WHERE
user.id = ?
", Long.parseLong(id)).first();
And here the models:
#Entity
public class User extends Model
{
#OneToOne(mappedBy = "user", fetch = FetchType.LAZY)
public UserOptions options;
// ...
}
#Entity
public class UserOptions extends Model
{
#OneToOne(fetch = FetchType.LAZY)
public User user;
}
The question is why play sends two query for the fetch query?
Thanks in advance
Okay, got it myself. The query is still the same.
The problem was, that custom queries are not cached by default. So I used this piece of code to provide a database cache (only for the current request).
// Get database cache instance
EhCacheImpl cache = EhCacheImpl.getInstance();
// Get cached user
User user = (User)cache.get("UserWithOptions_"+id);
// Check whether a user is cached
if(user == null)
{
// Get the user
user = User.find("SELECT user FROM User user LEFT JOIN FETCH user.options options WHERE user.id = ?", Long.parseLong(id)).first();
}
// Refresh cache
cache.add("UserWithOptions_"+id, user, 0);
May the force be with you!