These steps are discussed in more detail in the following sections.

Each class C of the Java Entity class model is coded as an annotated bean class with name C having a default constructor (with no parameters) and a constructor with entity creation parameters.

For instance, the Book class from the Entity class model is coded in the following way:

@Entity @Table( name="books")
@ViewScoped @ManagedBean( name="book")
public class Book {
  @Id @NotNull( message="An ISBN is required!")
  private String isbn;
  @Column( nullable=false)
  @NotNull( message="A title is required!")
  private String title;
  @Column( nullable=false)
  @NotNull( message="A year is required!")
  private Integer year;
  @ManyToOne( fetch=FetchType.EAGER)
  private Publisher publisher;

  public Book() {}
  public Book( String isbn, String title, 
      Integer year, Publisher publisher) {
    this.setIsbn( isbn);
    this.setTitle( title);
    this.setYear( year);
    this.setPublisher( publisher);
  }
  ...  // getters, setters, etc.
}

The @ManyToOne annotation on the property publisher is used for specifying the functionality type of the association Book has Publisher represented by the reference property publisher since it holds that a book has one publisher and a publisher has many books. This annotation also allows to specify a fetch type with the parameter fetch taking one of the following two possible values:

In the case of a single-valued reference property (representing a functional association) annotated with either @OneToOne or @ManyToOne, the default value is FetchType.EAGER, so referenced entities are fetched together with referencing entities, while in the case of a non-functional association (with either @OneToMany or @ManyToMany), the default value is FetchType.LAZY, so referenced entities are not fetched together with referencing entities, but have to be retrieved separately, if needed.

As a result of these JPA annotations, the following SQL table creation statement for creating the books table is generated:

CREATE TABLE IF NOT EXISTS `books` (
  `ISBN` varchar(10) NOT NULL,
  `TITLE` varchar(255) NOT NULL,
  `YEAR` int(11) NOT NULL,
  `PUBLISHER_NAME` varchar(255) DEFAULT NULL 
      FOREIGN  KEY (`PUBLISHER_NAME`) REFERENCES `publishers` (`NAME`)
);

Take care that all property constraints specified in the entity class model are properly coded by using suitable Bean Validation annotations, as explained in Part 2. For instance, for the name attribute, we have to use the JPA annotation @Id for specifying that the attribute corresponds to the primary key column of the database table to which the entity class is mapped, and the Bean Validation annotation @NotNull for defining a mandatory value constraint that is checked before an entity is saved to the database.

In the case of the address attribute, we have to define a mandatory value constraint in two forms: with the JPA annotation @Column( nullable=false) for the corresponding table column, and with the Bean Validation annotation @NotNull for the attribute.

@Id @NotNull( message="A name is required!")
private String name;

@Column( nullable=false)
@NotNull( message="An address is required!")
private String address;

Notice that, unfortunately, the current Java EE technology requires defining the same constraint twice, once for the database in the form of a JPA annotation, and once for the Java app in the form of a Bean Validation annotation.

Code the setter operations as (instance-level) methods. The setters only assign values and do not perform any validation, since the property constraints are only checked before save by the Java EE execution environment. The getters simply return the actual values of properties.

For any reference property, we have to choose and implement a deletion policy for taking care of the corresponding object destruction dependency in the delete method of the reference property's range class. In our case, we have to choose between

We choose the second policy, which can only be used inf the case of an optional reference property such as book.publisher. This is shown in the following code of the Publisher.delete method where for all book entities concerned the property book.publisher is cleared:

public static void delete( EntityManager em, UserTransaction ut, 
    String name) throw Exception {
  ut.begin();
  Publisher publisher = em.find( Publisher.class, name);
  // find all Books which have this publisher
  Query query = em.createQuery( 
      "SELECT b FROM Book b WHERE b.publisher.name = :name");
  query.setParameter( "name", name);
  List<Book> books = query.getResultList();
  // clear these books' publisher reference
  for ( Book b: books) { b.setPublisher( null);}
  em.remove( publisher);
  ut.commit();
}

The method loops through all Book entities referencing the publisher to be destroyed and sets their publisher property to null.

Based on JPA annotations, together with suitable converter classes when needed, serialization (from Java objects to table rows) as well as the corresponding de-serialization (from table columns to Java objects) are performed automatically.