jpa-2.0

问题 I'm trying to update my knowledge in Java, since I last used in when it was in 1.4.X version... I'm trying to use 1.6.0, in particular the Java Persistence API (2.0). I managed to create an entity class. It's working, since I'm able to store and retrieve data. But I was fooling around and when I decided to fill a JList with the column names of a table and didn't got success... It's a simple class and looks like: @Entity @Table(name = "T_CURRENCY", schema = "APP") public class Currency

问题 I'm relativley new to relational databases and I have some problems concerning the creation of queries. First I want to explain the situation shortly. I have several entity classes. All of them extend AbstractEntity or EntityProperty . So entities can have properties and properties have owning entities, so there is a bidirectional relation. Now let's say ConcreteEntity extends AbstractEntity and I want to create queries like this: Get all entities of type ConcreteEntity which has at least on

问题 I've a class Lawsuit , that contains a List<Hearing> , each one with a Date attribute. I need to select all the Lawsuit s ordered by the date of their Hearing s I've a CriteriaQuery like CriteriaBuilder cb = em.getCriteriaBuilder(); CriteriaQuery<Lawsuit> cq = cb.createQuery(Lawsuit.class); Root<Lawsuit> root = cq.from(Lawsuit.class); I use distinct to flatten the results: cq.select(root).distinct(true); I then join Lawsuit with Hearing Join<Lawsuit, Hearing> hearing = root.join("hearings",

问题 I've a class Lawsuit , that contains a List<Hearing> , each one with a Date attribute. I need to select all the Lawsuit s ordered by the date of their Hearing s I've a CriteriaQuery like CriteriaBuilder cb = em.getCriteriaBuilder(); CriteriaQuery<Lawsuit> cq = cb.createQuery(Lawsuit.class); Root<Lawsuit> root = cq.from(Lawsuit.class); I use distinct to flatten the results: cq.select(root).distinct(true); I then join Lawsuit with Hearing Join<Lawsuit, Hearing> hearing = root.join("hearings",

问题 I've a class Lawsuit , that contains a List<Hearing> , each one with a Date attribute. I need to select all the Lawsuit s ordered by the date of their Hearing s I've a CriteriaQuery like CriteriaBuilder cb = em.getCriteriaBuilder(); CriteriaQuery<Lawsuit> cq = cb.createQuery(Lawsuit.class); Root<Lawsuit> root = cq.from(Lawsuit.class); I use distinct to flatten the results: cq.select(root).distinct(true); I then join Lawsuit with Hearing Join<Lawsuit, Hearing> hearing = root.join("hearings",

问题 There is the possibility to disable the @OneToMany relationship join table with the @JoinColumn annotation. The default is a join table. What are the advantages and disadvantages for a production system for example? When should I use a join table and when not? Thank you. 回答1: By default @OneToMany will create a join table only if you'll use unidirectional relationship . In other words, if you have Employee and Project entities and the Employee entity is defined as follows (assume there is no

问题 When i was in college learning about web programming, they told us about hibernate. We used it for a while, i even had the chance to work with it in a real scenario in a company for almost 8 months. Now that i completely switching to Java EE 6 ( Im in love :) ), I use JPA for my ORM needs. It is being a few months since i use it, but i dont really understand what are the differences between one and other. Why some people say one or other is better or worse? The way i do my mappings and

问题 @Entity @Inheritance(strategy = InheritanceType.SINGLE_TABLE) @Table(name = "company_policies") @DiscriminatorColumn(name = "rule_name") public abstract class AbstractPolicyRule implements Serializable { @Transient private static final long serialVersionUID = 1L; @Id @GeneratedValue private Long id; private String value; ... } _ @Entity public class Category implements Serializable { @Transient private static final long serialVersionUID = 1L; @Id @GeneratedValue private Long id; @Column(name

问题 I have an in-memory data source: java.sql.Connection c = DriverManager.getConnection("jdbc:hsqldb:mem:testdb", "sa", ""); emf = Persistence.createEntityManagerFactory("manager"); But now I'm stuck. I want to use it as a JPA data source in a J2SE application. I've scoured the entire web but all info is related to J2EE. <persistence xmlns="http://java.sun.com/xml/ns/persistence" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://java.sun.com/xml/ns/persistence http

问题 I have 1 entity call Item in which I want to be able to link parent items to children. to use a join table to create a parent/child relationship. I haven't been able to get any good documentation on. So if anyone has any thoughts I'm all ears. Here is what I have... which works most of the time. public class Item implements java.io.Serializable { @Id private Long id; @ManyToOne(optional = true, fetch = FetchType.LAZY) @JoinTable(name = "ITEMTOITEM", joinColumns = { @JoinColumn(name = "ITEMID"