Hibernate的那些事-manyToOne注解映射(List集合)

1:定义一个Group类，在映射关系中为一的一方：

package collections.list;

import java.util.ArrayList;
import java.util.List;
import javax.persistence.CascadeType;
import javax.persistence.Entity;
import javax.persistence.GeneratedValue;
import javax.persistence.Id;
import javax.persistence.OneToMany;
import javax.persistence.OrderBy;
import javax.persistence.Table;

@Entity
@Table(name = "t_list_group")
public class Group {
private int id;
private String name;
private List<User> users = new ArrayList<User>();

@Id
@GeneratedValue
public int getId() {
return id;
}

public void setId(int id) {
this.id = id;
}

public String getName() {
return name;
}

public void setName(String name) {
this.name = name;
}

@OneToMany(mappedBy = "group", cascade = { CascadeType.ALL })
@OrderBy("name ASC")
public List<User> getUsers() {
return users;
}

public void setUsers(List<User> users) {
this.users = users;
}

}
2:定义一个User类，映射中多的一方：

package collections.list;

import javax.persistence.CascadeType;
import javax.persistence.Entity;
import javax.persistence.GeneratedValue;
import javax.persistence.Id;
import javax.persistence.ManyToOne;
import javax.persistence.Table;

@Entity
@Table(name = "t_list_user")
public class User {
private int id;
private String name;
private Group group;

@ManyToOne(cascade = CascadeType.ALL)
public Group getGroup() {
return group;
}

public void setGroup(Group group) {
this.group = group;
}

@Id
@GeneratedValue
public int getId() {
return id;
}

public void setId(int id) {
this.id = id;
}

public String getName() {
return name;
}

public void setName(String name) {
this.name = name;
}

}
在hibernate.cfg.xml中添加对实体的映射：

<mapping class="collections.list.Group" />
<mapping class="collections.list.User" />

这里我们使用的是注解映射，要特别与使用映射文件的映射公开来;

同时也要注意一个问题(在hibernate.cfg.xml文件中不能将两种混用，否则会出错)

3：使用Junit对这个映射进行测试：

package collections.list;

import org.hibernate.Session;
import org.hibernate.SessionFactory;
import org.hibernate.cfg.AnnotationConfiguration;
import org.hibernate.tool.hbm2ddl.SchemaExport;
import org.junit.AfterClass;
import org.junit.BeforeClass;
import org.junit.Test;

public class TestListJunit {

/**
* @param args
*/

private static SessionFactory sessionFactory;

@BeforeClass
public static void beforClass() {
new SchemaExport(new AnnotationConfiguration().configure()).create(
false, true);

sessionFactory = new AnnotationConfiguration().configure()
.buildSessionFactory();

}

@AfterClass
public static void afterClass() {
if (sessionFactory != null) {
sessionFactory.close();
}

}

@Test
public void testSavaEntity() {
Session session = sessionFactory.getCurrentSession();
session.beginTransaction();

Group group = new Group();
group.setName("animal");
User user = new User();
user.setName("little dog");
user.setGroup(group);
User user1 = new User();
user1.setName("little cat");
user1.setGroup(group);

group.getUsers().add(user);
group.getUsers().add(user1);

session.save(group);
session.save(user);
session.save(user1);
session.getTransaction().commit();

}

public static void main(String[] args) {

beforClass();
}
}