Embeddable classes
An entity may use other fine-grained classes to represent entity state.
Instances of these classes, unlike entity instances, do not have persistent
identity of their own. Instead, they exist only as part of the state of the
entity to which they belong. (From 2.0 Proposed Final Draft March 13, 2009
-- do I need to provide footnote or something?)
In short, an embeddable is a seperation of data into a Java class that
relies on the owning Entity for it's identity. Many(most) times an
embeddable resides in the same database row as the owning Entity.
Review the getting started
page on how to run the samples.
Samples
| Schema |
|---|
 |
| Class diagram |
|---|
|
Collections of Embeddables
In the code snippet below, there is a User Entity which has a collection of
Embedded addresses.
@Embeddable
public class Address {
@Basic
private String street;
@Basic
private String city;
@Basic
private String state;
@Basic
private Integer zip;
public Address(){
}
//...
}
@Entity
public class User {
@Id
@GeneratedValue(strategy=GenerationType.IDENTITY)
private int id;
@ElementCollection
@CollectionTable(name="user_address")
private Set<Address> addresses = new HashSet<Address>();
public User(){
}
//...
}
...
// Select Entity based off a query over a collection of embeddables
Query q = em.createQuery("SELECT u FROM User u , in (u.addresses) a WHERE a.state='xx'");
// TODO -- add more!
...
Relationships from Embeddables
In the code snippet below, there is an Address embeddable with a ManyToOne
relationship to a Coordinates Entity.
@Embeddable
public class Address {
@Basic
private String street;
@Basic
private String city;
@Basic
private String state;
@Basic
private Integer zip;
@ManyToOne(cascade=CascadeType.ALL)
Coordinates coordinates;
public Address(){
}
//...
}
@Entity
public class Coordinates {
@Id
@GeneratedValue(strategy=GenerationType.IDENTITY)
int id;
@Basic
double longitude;
@Basic
double latitude;
public Coordinates(){
}
public Coordinates(double lon, double lat){
longitude=lon;
latitude=lat;
}
//...
}
...
// Embedded -> relationship traversal
Query q = em.createQuery("SELECT u FROM User u , in (u.addresses) a WHERE a.coordinates.longitude=xxx");
// TODO -- add more!
...
Nested Embeddables
In the code snippet below, there is a User Entity which has an embedded
ContactInfo. ContactInfo contains two other embeddeded embeddables, Address
and Phone.
@Embeddable
public class Address {
@Basic
private String street;
@Basic
private String city;
@Basic
private String state;
@Basic
private Integer zip;
public Address(){
}
//...
}
@Embeddable
public class Phone {
@Basic
private String phone_number;
@Basic
private String phone_type;
//...
}
@Embeddable
public class ContactInfo {
public ContactInfo(){
}
@Embedded
Address homeAddress;
@Embedded
Phone homePhone;
//...
}
@Entity
public class User {
@Id
@GeneratedValue(strategy=GenerationType.IDENTITY)
private int id;
@Embedded
ContactInfo contactInfo;
public User(){
}
//...
}
...
// Nested embeddables traversal
Query q = em.createQuery("SELECT u FROM User u WHERE u.contactInfo.homePhone.number='507-555-5555' " +
"AND u.contactInfo.homePhone.type='cell'");
// TODO -- add more!
...
