Annotations for Persistence
Some of you might already know of the fictional music company called Watermelon. I've used it in two previous articles about JPA ("
Master the New Persistence Paradigm with JPA" and "
Persistence Pays Offs: Advanced Mapping with JPA"). If you think of JAXB as a way to persist data into XML, JPA is its counterpart in terms of relational databases. In fact, both technologies rely heavily on annotations. That means that the same class can be annotated by JPA and JAXB annotations and, in this way, can give an XML representation as well as be persisted in a database.
For those of you interested in this double use of annotations, you will find an example in the code download. But just to give you a taste, here is what the Address class would look like:
@Entity
@Table(name = "t_address")
@XmlType(propOrder = {"street", "zipcode", "city", "country"})
@XmlAccessorType(XmlAccessType.FIELD)
public class Address {
@XmlTransient
@Id @GeneratedValue
private Long id;
private String street;
@Column(length = 100)
private String city;
@Column(name = "zip_code", length = 10)
@XmlElement(name = "zip")
private String zipcode;
@Column(length = 50)
private String country;
@XmlTransient
@ManyToMany(cascade = CascadeType.PERSIST)
@JoinTable(name = "t_address_tag",
joinColumns = {@JoinColumn(name = "address_fk")},
inverseJoinColumns = {@JoinColumn(name = "tag_fk")})
private List<Tag> tags = new ArrayList<Tag>();
// Constructors, getters, setters
}
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