hibernate
Mappages d'association entre entités

Association OneToMany

Pour illustrer la relation OneToMany, nous avons besoin de 2 entités, par exemple, pays et ville. Un pays a plusieurs villes.

Dans la CountryEntity ci-dessous, nous définissons un ensemble de villes pour le pays.

@Entity
@Table(name = "Country")
public class CountryEntity implements Serializable
{
   private static final long serialVersionUID = 1L;
 
   @Id
   @Column(name = "COUNTRY_ID", unique = true, nullable = false)
   @GeneratedValue(strategy = GenerationType.SEQUENCE)
   private Integer           countryId;
 
   @Column(name = "COUNTRY_NAME", unique = true, nullable = false, length = 100)
   private String            countryName;

   @OneToMany(mappedBy="country", fetch=FetchType.LAZY)
   private Set<CityEntity> cities = new HashSet<>();

   //Getters and Setters are not shown
}

Maintenant l'entité de la ville.

@Entity
@Table(name = "City")
public class CityEntity implements Serializable
{
   private static final long serialVersionUID = 1L;
 
   @Id
   @Column(name = "CITY_ID", unique = true, nullable = false)
   @GeneratedValue(strategy = GenerationType.SEQUENCE)
   private Integer           cityId;
 
   @Column(name = "CITY_NAME", unique = false, nullable = false, length = 100)
   private String            cityName;

   @ManyToOne(optional=false, fetch=FetchType.EAGER)
   @JoinColumn(name="COUNTRY_ID", nullable=false)
   private CountryEntity country;
 
   //Getters and Setters are not shown
}

Une à plusieurs associations utilisant XML

Ceci est un exemple de la façon dont vous effectueriez un mappage un à plusieurs avec XML. Nous utiliserons Author and Book comme exemple et supposons qu'un auteur a peut-être écrit de nombreux livres, mais que chaque livre n'aura qu'un auteur.

Classe d'auteur:

public class Author {
    private int id;
    private String firstName;
    private String lastName;
    
    public Author(){
        
    }
    public int getId(){
        return id;
    }
    public void setId(int id){
        this.id = id;
    }
    public String getFirstName(){
        return firstName;
    }
    public void setFirstName(String firstName){
        this.firstName = firstName;
    }
    public String getLastName(){
        return lastName;
    }
    public void setLastName(String lastName){
        this.lastName = lastName;
    }
}

Classe de livre:

public class Book {
    private int id;
    private String isbn;
    private String title;    
    private Author author;
    private String publisher;
    
    public Book() {
        super();
    }
    public int getId() {
        return id;
    }
    public void setId(int id) {
        this.id = id;
    }
    public String getIsbn() {
        return isbn;
    }
    public void setIsbn(String isbn) {
        this.isbn = isbn;
    }
    public String getTitle() {
        return title;
    }
    public void setTitle(String title) {
        this.title = title;
    }
    public Author getAuthor() {
        return author;
    }
    public void setAuthor(Author author) {
        this.author = author;
    }
    public String getPublisher() {
        return publisher;
    }
    public void setPublisher(String publisher) {
        this.publisher = publisher;
    }
}

Author.hbm.xml:

<?xml version="1.0"?>
<!DOCTYPE hibernate-mapping PUBLIC
    "-//Hibernate/Hibernate Mapping DTD//EN"
    "http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd" >

<hibernate-mapping>
   <class name="Author" table="author">
      <meta attribute="class-description">
         This class contains the author's information. 
      </meta>
      <id name="id" type="int" column="author_id">
         <generator class="native"/>
      </id>
      <property name="firstName" column="first_name" type="string"/>
      <property name="lastName" column="last_name" type="string"/>
   </class>
</hibernate-mapping>

Book.hbm.xml:

<?xml version="1.0"?>
<!DOCTYPE hibernate-mapping PUBLIC
    "-//Hibernate/Hibernate Mapping DTD//EN"
    "http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd" >

<hibernate-mapping>
    <class name="Book" table="book_title">
      <meta attribute="class-description">
         This class contains the book information. 
      </meta>
        <id name="id" type="int" column="book_id">
            <generator class="native"/>
        </id>
        <property name="isbn" column="isbn" type="string"/>
        <property name="title" column="title" type="string"/>
         <many-to-one name="author" class="Author" cascade="all">
             <column name="author"></column>
         </many-to-one>
        <property name="publisher" column="publisher" type="string"/>
    </class>
</hibernate-mapping>

Ce qui rend la connexion un à plusieurs, c'est que la classe Book contient un auteur et que le fichier XML a la balise <many-to-one>. L'attribut en cascade vous permet de définir la manière dont l'entité enfant sera enregistrée / mise à jour.