Hibernate关联关系的CRUD和集合映射(annotation)

设定cascade可以设定在持久化时对于关联对象的操作。cascade的属性指明在做什么操作的时候关联对象是绑定在一起的。

双向关联：

1.设定mappedBy

2.在程序中要设定双向关联(对象之间)

cascade管的是增删改，而fecth管的是读取

一对多关系中，一的一方，默认的fecth为LAZY，而多一方，默认的fecth为EARGE

LAZY只能取到本身对象，而EARGE可以取到关联对象

Group.java

package com.test.hiberenate.model;

import java.util.HashMap;
import java.util.Map;

import javax.persistence.CascadeType;
import javax.persistence.Entity;
import javax.persistence.GeneratedValue;
import javax.persistence.Id;
import javax.persistence.MapKey;
import javax.persistence.OneToMany;
import javax.persistence.Table;

@Entity
@Table(name = "t_group")
public class Group {
	private int id;
	private String name;
	//private Set<User> users = new HashSet<User>();
	//private List<User> users = new ArrayList<User>();
	private Map<Integer, User> users = new HashMap<Integer, 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)
	public Set<User> getUsers() {
		return users;
	}

	public void setUsers(Set<User> users) {
		this.users = users;
	}*/
	
/*	@OneToMany(mappedBy = "group", cascade = CascadeType.ALL)
	@OrderBy("name desc")// 指定按照User中name的降序排列
	public List<User> getUsers() {
		return users;
	}
	
	public void setUsers(List<User> users) {
		this.users = users;
	}*/
	
	@OneToMany(mappedBy = "group", cascade = CascadeType.ALL)
	@MapKey(name = "id")// 指定map中的key为User中的id
	public Map<Integer, User> getUsers() {
		return users;
	}

	public void setUsers(Map<Integer, User> users) {
		this.users = users;
	}

}

 

User.java

package com.test.hiberenate.model;

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

@Entity
@Table(name = "t_user")
public class User {
	private int id;
	private String name;
	private 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;
	}

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

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

}

 

HibernateORMappingTest.java

package com.test.hibernate.model;

import java.util.Map;

import org.hibernate.HibernateException;
import org.hibernate.Session;
import org.hibernate.SessionFactory;
import org.hibernate.Transaction;
import org.hibernate.cfg.Configuration;
import org.junit.AfterClass;
import org.junit.BeforeClass;
import org.junit.Test;

import com.test.hiberenate.model.Group;
import com.test.hiberenate.model.User;

public class HibernateORMappingTest {
	private static SessionFactory sf = null;

	@BeforeClass
	public static void beforeClass() {
		//new SchemaExport(new Configuration().configure()).create(false, true);
		try {
			if (sf == null) {
				sf = new Configuration().configure().buildSessionFactory();
			}
		} catch (HibernateException e) {
			e.printStackTrace();
		}
	}

	@AfterClass
	public static void afterClass() {
		sf.close();
	}

/*	@Test
	public void testSaveGroup() {
		Group group = new Group();
		group.setName("人力资源部");

		User user1 = new User();
		user1.setName("张三");
		user1.setGroup(group);

		User user2 = new User();
		user2.setName("李四");
		user2.setGroup(group);

		User user3 = new User();
		user3.setName("王五");
		user3.setGroup(group);

		group.getUsers().add(user1);
		group.getUsers().add(user2);
		group.getUsers().add(user3);

		Session session = sf.getCurrentSession();
		Transaction t = session.beginTransaction();
		session.save(group);
		t.commit();
	}

	@Test
	public void testGroupForList() {
		testSaveGroup();
		Session session = sf.getCurrentSession();
		Transaction t = session.beginTransaction();
		Group group = (Group) session.get(Group.class, 1);
		List<User> lstUser = group.getUsers();
		for (int i = 0; i < lstUser.size(); i++) {
			System.out.println(lstUser.get(i).getName());
		}
		t.commit();

	}*/
	
	@Test
	public void testGroupForMap() {
		Session session = sf.getCurrentSession();
		Transaction t = session.beginTransaction();
		Group group = (Group) session.get(Group.class, 1);
		Map<Integer, User> mUser = group.getUsers();
		for (Map.Entry<Integer, User> entry : mUser.entrySet()) {
			System.out.println(entry.getKey() + ":" + entry.getValue().getName());
		}
		t.commit();
		
	}

	public static void main(String[] args) {
		beforeClass();
	}

}