jpa-2.0

问题 Is it true that @JoinColumn can be used on both side of One to One relationship in JPA ? I was under impression that it should be always used in owning side of One to One relationship as owning side will have foreign key column and this annotation define the attribute of foreign key column . Please clarify if my understanding is not correct . Edit #1 - I wanted to know , In which scenario we will be using @JoinColumn annotation on both side of one to one relationship ? 回答1: The OneToOne

问题 Is is possible (without writing custom SQL) to have Eclipselink trust me as to whether to perform an update or insert on a merge, rather than perform a select, then an update or insert? If so, how? In my mind I'd like to use a transient flag and a custom if statement to determine whether the item is already in the database or not, and instruct eclipselink to perform the query required. I understand Hibernate provides this as update() and save() A few notable points: I have a large amount of

问题 Is is possible (without writing custom SQL) to have Eclipselink trust me as to whether to perform an update or insert on a merge, rather than perform a select, then an update or insert? If so, how? In my mind I'd like to use a transient flag and a custom if statement to determine whether the item is already in the database or not, and instruct eclipselink to perform the query required. I understand Hibernate provides this as update() and save() A few notable points: I have a large amount of

问题 In hibernate I want to run this JPQL / HQL query: select new org.test.userDTO( u.id, u.name, u.securityRoles) FROM User u WHERE u.name = :name userDTO class: public class UserDTO { private Integer id; private String name; private List<SecurityRole> securityRoles; public UserDTO(Integer id, String name, List<SecurityRole> securityRoles) { this.id = id; this.name = name; this.securityRoles = securityRoles; } ...getters and setters... } User Entity: @Entity public class User { @id private

问题 I have an entity annotated with @Entity . If I am responsible for creating the CREATE TABLE scripts why should I specify @Column( nullable = false ) when I can create a column in the database with the NOT NULL keywords? Is there any example that shows the benefits of using this property in a field? 回答1: Better error messages and error handling, especially if you also add the JSR303 @NotNull annotation. If you create the column as NOT NULL but don't tell JPA it's not null, JPA will assume that

问题 I trying to use the Open Session in View pattern, but everytime I try to catch the EntityManager in my ManagedBean the entityManager come NULL here is how I'm doing: package filters; // imports.. public class JPAFilter implements Filter { private EntityManagerFactory factory; @Override public void doFilter(ServletRequest request, ServletResponse response, FilterChain chain) throws IOException, ServletException { EntityManager entityManager = this.factory.createEntityManager(); request

问题 With JPA 2 Criteria Join method I can do the following: //Join Example (default inner join) int age = 25; CriteriaBuilder cb = entityManager.getCriteriaBuilder(); CriteriaQuery<Team> c = cb.createQuery(Team.class); Root<Team> t = c.from(Team.class); Join<Team, Player> p = t.join(Team_.players); c.select(t).where(cb.equal(p.get(Player_.age), age)); TypedQuery<Team> q = entityManager.createQuery(c); List<Team> result = q.getResultList(); How can I do the same with fetch method, I expected that

问题 We are working on a little web (will run on Tomcat) with the data layer done with JPA (Eclipselink). I did similar thing some time ago. But i were always unsure when i need to begin and end transactions or do a flush. At the moment i use transaction if i add (persist) and remove objects. If i call setters on an already persisted object i do not use transactions. Is there a guide/ tutorial or a short answer when to use transactions or how to implement application managed JPA correctly. 回答1: I

问题 I'm having trouble with a JPA/Hibernate (3.5.3) setup, where I have an entity, an "Account" class, which has a list of child entities, "Contact" instances. I'm trying to be able to add/remove instances of Contact into a List<Contact> property of Account. Adding a new instance into the set and calling saveOrUpdate(account) persists everything lovely. If I then choose to remove the contact from the list and again call saveOrUpdate, the SQL Hibernate seems to produce involves setting the account

问题 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