前面的關於Hibernate的文章講解的知識比較多了,今天這篇文章就不鋪墊了,直接上代碼,我們一起來看看註釋。今天使用的關係是人與地址的關係,例子找的不太好,忍耐一下!
先看持久化類(註解是重點):
Person:
@Entity
@Table(name="person_inf")
// 多對多的映射必須存在一箇中間表
public class Person {
// 標識屬性
@Id@Column(name="person_id")
// 設置主鍵的映射策略
@GeneratedValue(strategy=GenerationType.IDENTITY)
private Integer id;
private String name;
private int age;
// 定義該Person實體所有關聯的Address實體
@ManyToMany(targetEntity=Address.class)
// 映射連接表,指定連接表的名字是person_address
@JoinTable(name="person_address",
// 映射連接表中名爲person_id的外鍵列,該列參照當前實體對應表的person_id主鍵列
joinColumns = @JoinColumn(referencedColumnName="person_id",name="person_id"),
// 映射連接表中名爲address_id的外鍵列,該列參照當前實體的關聯實體對應標的address_id主鍵列
inverseJoinColumns = @JoinColumn(referencedColumnName="address_id",name="address_id")
)
private Set<Address> addresses = new HashSet<>();
// 省略set、get方法以及構造器方法...
}
Address:
@Entity
@Table(name="address_inf")
public class Address {
@Id@Column(name="address_id")
@GeneratedValue(strategy=GenerationType.IDENTITY)
private int addressId;
private String addressDetail;
@ManyToMany(targetEntity=Person.class)
@JoinTable(name="person_address",
joinColumns=@JoinColumn(referencedColumnName="address_id",name="address_id"),
inverseJoinColumns=@JoinColumn(referencedColumnName="person_id",name="person_id")
)
private Set<Person> persons = new HashSet<>();
// 省略set、get方法以及構造器方法...
}
然後cfg核心配置文件的配置與之前有點不同,現在不存在hbm配置文件,Annotation都存在於持久化類中,直接如下配置:
<mapping class="edu.ctgu.hibernate.many2many.Person"/>
<mapping class="edu.ctgu.hibernate.many2many.Address"/>
測試方法:
public class Many2Many {
private SessionFactory factory = null;
private Session session = null;
private Transaction transaction = null;
@Before
public void testBefore(){
// 1.初始化配置文件加載配置信息,默認加載src目錄下的hibernate.cfg.xml文件
Configuration configuration = new Configuration().configure();
// 2.初始化SessionFactory
factory = configuration.buildSessionFactory();
// 3.打開Session
session = factory.openSession();
// 4.開啓事務
transaction = session.beginTransaction();
}
@After
public void testAfter(){
transaction.commit();
session.close();
factory.close();
}
@Test
public void testGet(){
Person person = session.get(Person.class, 10);
System.out.println(person.getName());
// 遍歷與指定person關聯的address類的集合
Iterator<Address> iterator = person.getAddresses().iterator();
while (iterator.hasNext()) {
Address address = iterator.next();
System.out.println(address);
}
}
@Test
public void testSave(){
// 這就是基本的次序了
Person p = new Person("饒大大",21);
session.save(p);
Address a = new Address("襄陽樊城");
a.getPersons().add(p);
session.save(a);
Address a2 = new Address("武漢武昌");
a2.getPersons().add(p);
session.save(a2);
Person p2 = new Person("愛麗絲",20);
p2.getAddresses().add(a2);
p2.getAddresses().add(a);
session.save(p2);
}
@Test
public void test(){
}
}
上面的測試方法值得講解一下。首先在執行空的test測試方法時,Hibernate打印的SQL語句如下:
Hibernate:
create table address_inf (
address_id integer not null auto_increment,
addressDetail varchar(255),
primary key (address_id)
)
Hibernate:
create table person_address (
address_id integer not null,
person_id integer not null,
primary key (person_id, address_id)
)
Hibernate:
create table person_inf (
person_id integer not null auto_increment,
age integer not null,
name varchar(255),
primary key (person_id)
)
Hibernate:
alter table person_address
add constraint FK2ppxjvtgnqmym2pcrnw1rxpmo
foreign key (person_id)
references person_inf (person_id)
Hibernate:
alter table person_address
add constraint FKkkw06n97i6bwjpiohmqvby97
foreign key (address_id)
references address_inf (address_id)
創建了三個表,其中表person_address就是多對多映射中必須存在的連接表,然後再爲連接表設置兩個外鍵映射(其實連接表中的兩個數據列爲主鍵元組),分別映射主表的主鍵。
然後重點來了,我們看一下測試save的代碼塊,注意插入的順序。開始一個Person對象被單一保存,然後設置兩個地址關聯到Person對象;最後一個Person直接關聯兩個Address對象。目前在我看來這是一個符合邏輯的執行次序。
其他方法大家一一測試,相信會學到很多的東西。