It is really a good idea but unfortunately directly mapping interfaces as an entity attribute is not supported by JPA. You can only map top level classes directly annotated with @Entity. This top level class may implement an interface though. This feature has been requested and discussed for a long time. Also take a look … Read more
Use the following form: SELECT e FROM Employee e WHERE e.active = TRUE See the docs for more info.
I solved my problem placing the insertable=false, updatable=false in the @JoinColumn annotation in both classes, Person and Company.
Using the annotation @Column(insertable = false) will prevent the value being generated in the sql.
Agree with you about that method, and the fact that you would expect it to allow what you say. Another option would be Join<Team, Player> p = t.join(Team_.players); t.fetch(Team_.players); c.select(t).where(cb.equal(p.get(Player_.age), age)); i.e do a join(), add a fetch() for it, and then make use of the join. This is illogical and only adds to the … Read more
JPA does not limit number of persistence units defined in persistence.xml. This warning just tells about limitation of tool in Eclipse IDE. This is told for example here http://www.eclipse.org/webtools/dali/gettingstarted.php : Currently Dali only supports one Persistence Unit and one Persistence XML file per project. Other configurations can exist in a JPA project, but the validation … Read more
You cannot catch ConstraintViolationException.class because it’s not propagated to that layer of your code, it’s caught by the lower layers, wrapped and rethrown under another type. So that the exception that hits your web layer is not a ConstraintViolationException. In my case, it’s a TransactionSystemException. I’m using @Transactional annotations from Spring with the JpaTransactionManager. The … Read more
Below is the pseudo-code for using sub-query using Criteria API. CriteriaBuilder criteriaBuilder = entityManager.getCriteriaBuilder(); CriteriaQuery<Object> criteriaQuery = criteriaBuilder.createQuery(); Root<EMPLOYEE> from = criteriaQuery.from(EMPLOYEE.class); Path<Object> path = from.get(“compare_field”); // field to map with sub-query from.fetch(“name”); from.fetch(“id”); CriteriaQuery<Object> select = criteriaQuery.select(from); Subquery<PROJECT> subquery = criteriaQuery.subquery(PROJECT.class); Root fromProject = subquery.from(PROJECT.class); subquery.select(fromProject.get(“requiredColumnName”)); // field to map with main-query subquery.where(criteriaBuilder.and(criteriaBuilder.equal(“name”,name_value),criteriaBuilder.equal(“id”,id_value))); select.where(criteriaBuilder.in(path).value(subquery)); … Read more
select distinct distributor from Distributor distributor join distributor.towns town join town.district district where district.name = :name See: https://en.wikibooks.org/wiki/Java_Persistence/JPQL
You can do a boolean query using a case expression. As of JPA 2.0 (Java EE 6) you can create a TypedQuery . String query = “select case when (count(*) > 0) then true else false end from ……” TypedQuery<Boolean> booleanQuery = entityManager.createQuery(query, Boolean.class); boolean exists = booleanQuery.getSingleResult(); In JPA 1.0 (Java EE 5) you … Read more