Hibernate多对多

数据库的多对多：
数据库中不能直接映射多对多
处理：创建一个桥接表(中间表)，将一个多对多关系转换成两个一对多
注：数据库多表联接查询，永远就是二个表的联接查询

hibernate的多对多：
hibernate可以直接映射多对多关联关系(看作两个一对多)

多对多关系注意事项：一定要定义一个主控方

讲解下一对多的自联：

TreeNode.hbm.xml

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE hibernate-mapping PUBLIC 
    "-//Hibernate/Hibernate Mapping DTD 3.0//EN"
    "http://www.hibernate.org/dtd/hibernate-mapping-3.0.dtd">
<hibernate-mapping>
	<class name="com.xzy.four.entity.TreeNode" table="t_hibernate_sys_tree_node">
		<id name="nodeId" type="java.lang.Integer" column="tree_node_id">
			<generator class="increment" />
		</id>
		<property name="nodeName" type="java.lang.String"
			column="tree_node_name">
		</property>
		<property name="treeNodeType" type="java.lang.Integer"
			column="tree_node_type">
		</property>
		<property name="position" type="java.lang.Integer"
			column="position">
		</property>
		<property name="url" type="java.lang.String"
			column="url">
		</property>
		
		<many-to-one name="parent" class="com.xzy.four.entity.TreeNode" column="parent_node_id"/>
		
		<set name="children" cascade="save-update" inverse="true">
			<key column="parent_node_id"></key>
			<one-to-many class="com.xzy.four.entity.TreeNode"/>
		</set>
	</class>
</hibernate-mapping>

TreeNode.java

package com.xzy.four.entity;

import java.util.HashSet;
import java.util.Set;

public class TreeNode {
	private Integer nodeId;
	private String nodeName;
	private Integer treeNodeType;
	private Integer position;
	private String url;
	private TreeNode parent;
	private Set<TreeNode> children = new HashSet<TreeNode>();
	private Integer initChildren = 0;
//	0代表懒加载； 1代表强制加载(子节点)； 2强制加载用户； 3强制加载两个。

	public Integer getNodeId() {
		return nodeId;
	}

	public void setNodeId(Integer nodeId) {
		this.nodeId = nodeId;
	}

	public String getNodeName() {
		return nodeName;
	}

	public void setNodeName(String nodeName) {
		this.nodeName = nodeName;
	}

	public Integer getTreeNodeType() {
		return treeNodeType;
	}

	public void setTreeNodeType(Integer treeNodeType) {
		this.treeNodeType = treeNodeType;
	}

	public Integer getPosition() {
		return position;
	}

	public void setPosition(Integer position) {
		this.position = position;
	}

	public String getUrl() {
		return url;
	}

	public void setUrl(String url) {
		this.url = url;
	}

	public TreeNode getParent() {
		return parent;
	}

	public void setParent(TreeNode parent) {
		this.parent = parent;
	}

	public Set<TreeNode> getChildren() {
		return children;
	}

	public void setChildren(Set<TreeNode> children) {
		this.children = children;
	}

	public Integer getInitChildren() {
		return initChildren;
	}

	public void setInitChildren(Integer initChildren) {
		this.initChildren = initChildren;
	}

//	@Override
//	public String toString() {
//		return "TreeNode [nodeId=" + nodeId + ", nodeName=" + nodeName + ", treeNodeType=" + treeNodeType
//				+ ", position=" + position + ", url=" + url + ", children=" + children + "]";
//	}

	@Override
	public String toString() {
		return "TreeNode [nodeId=" + nodeId + ", nodeName=" + nodeName + ", treeNodeType=" + treeNodeType
				+ ", position=" + position + ", url=" + url + "]";
	}
	

}

TreeNodeDao.java

public class TreeNodeDao {
	public TreeNode load(TreeNode treeNode) {
		Session session = SessionFactoryUtils.openSession();
		Transaction transaction = session.beginTransaction();
		TreeNode t = session.load(TreeNode.class, treeNode.getNodeId());
		if(t != null && new Integer(1).equals(treeNode.getInitChildren())) {
			Hibernate.initialize(t.getChildren());
			Hibernate.initialize(t.getParent());
		}
		transaction.commit();
		session.close();
		return t;
	}
}

	@Test
	public void testLoad() {
		TreeNode treeNode = new TreeNode();
		treeNode.setNodeId(6);
		treeNode.setInitChildren(1);
		
		TreeNode t = this.treeNodeDao.load(treeNode);
		System.out.println(t);
		System.out.println(t.getParent());
		System.out.println(t.getChildren());
	}

案例：

书本表：t_hibernate_book

书本类型表：t_hibernate_category

关联表：t_hibernate_book_category

-- 书本类别表
create table t_hibernate_category
(
   category_id int primary key auto_increment,
   category_name varchar(50) not null
);

-- 书本表
create table t_hibernate_book
(
   book_id int primary key auto_increment,
   book_name varchar(50) not null,
   price float not null
);


-- 桥接表
-- 定义三个列，其实只要两个列
-- 一个类别对应多本书，一本书对应多个类别
create table t_hibernate_book_category
(
  bcid int primary key auto_increment,  
  bid int not null,
  cid int not null,
  foreign key(bid) references t_hibernate_book(book_id),
  foreign key(cid) references t_hibernate_category(category_id)
);

多对多的配置文件介绍

book.hbm.xml:

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE hibernate-mapping PUBLIC 
    "-//Hibernate/Hibernate Mapping DTD 3.0//EN"
    "http://www.hibernate.org/dtd/hibernate-mapping-3.0.dtd">
<hibernate-mapping>
	<class name="com.xzy.four.entity.Book" table="t_hibernate_book">
		<cache usage="read-only" region="com.zking.five.entity.Book"/>
		<id name="bookId" type="java.lang.Integer" column="book_id">
			<generator class="increment" />
		</id>
		<property name="bookName" type="java.lang.String"
			column="book_name">
		</property>
		<property name="price" type="java.lang.Float"
			column="price">
		</property>
		
		<!-- 
			table:代表的是中间表
			name：书籍类的关联属性
			inverse：中间表交于对方维护
			key：当前类对应的表列段在中间表（t_hibernate_book_category）的外键(bid)
			many-to-many
				column：对应的是上面key查出来中间表（t_hibernate_book_category）的另一个字段(cid)，当作关联表的主键(category_id)进行查询
				class ：上述查出来的主键对应的实体类
			-->
		 
		<set table="t_hibernate_book_category" name="categories" cascade="save-update" inverse="false">
			<!-- one -->
			<key column="bid"></key>
			<!-- many -->
			<many-to-many column="cid" class="com.xzy.four.entity.Category"></many-to-many>
		</set>
	</class>
</hibernate-mapping>

category.hbm.xml:

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE hibernate-mapping PUBLIC 
    "-//Hibernate/Hibernate Mapping DTD 3.0//EN"
    "http://www.hibernate.org/dtd/hibernate-mapping-3.0.dtd">
<hibernate-mapping>
	<class name="com.xzy.four.entity.Category" table="t_hibernate_category">
		<id name="categoryId" type="java.lang.Integer" column="category_id">
			<generator class="increment" />
		</id>
		<property name="categoryName" type="java.lang.String"
			column="category_name">
		</property>
		
		<set table="t_hibernate_book_category" name="books" cascade="save-update" inverse="true">
			<key column="cid"></key>
			<many-to-many column="bid" class="com.xzy.four.entity.Book"></many-to-many>
		</set>
	</class>
</hibernate-mapping>

注意：key对应的column不要填反，这里填的是当前类所映射的表的主键，所对应的桥接表中的外键

书本：Book.java

package com.xzy.four.entity;

import java.io.Serializable;
import java.util.HashSet;
import java.util.Set;

public class Book implements Serializable{
//	book_id int primary key auto_increment,
//	   book_name varchar(50) not null,
//	   price float not null
	private Integer bookId;
	private String bookName;
	private Float price;
	
	private Set<Category> categories = new HashSet<Category>();
	private Integer initCategories = 0;

	public Integer getInitCategories() {
		return initCategories;
	}

	public void setInitCategories(Integer initCategories) {
		this.initCategories = initCategories;
	}

	public Integer getBookId() {
		return bookId;
	}

	public void setBookId(Integer bookId) {
		this.bookId = bookId;
	}

	public String getBookName() {
		return bookName;
	}

	public void setBookName(String bookName) {
		this.bookName = bookName;
	}

	public Float getPrice() {
		return price;
	}

	public void setPrice(Float price) {
		this.price = price;
	}

	public Set<Category> getCategories() {
		return categories;
	}

	public void setCategories(Set<Category> categories) {
		this.categories = categories;
	}

	@Override
	public String toString() {
		return "Book [bookId=" + bookId + ", bookName=" + bookName + ", price=" + price + "]";
	}

	public Book(Integer bookId, String bookName) {
		super();
		this.bookId = bookId;
		this.bookName = bookName;
	}

	public Book() {
		super();
	}
	
	
}

书本类型：category.java

package com.xzy.four.entity;

import java.io.Serializable;
import java.util.HashSet;
import java.util.Set;

public class Category implements Serializable{
//	category_id int primary key auto_increment,
//	   category_name varchar(50) not null
	private Integer categoryId;
	private String categoryName;
	private Set<Book> books = new HashSet<Book>();
	public Integer getCategoryId() {
		return categoryId;
	}
	public void setCategoryId(Integer categoryId) {
		this.categoryId = categoryId;
	}
	public String getCategoryName() {
		return categoryName;
	}
	public void setCategoryName(String categoryName) {
		this.categoryName = categoryName;
	}
	public Set<Book> getBooks() {
		return books;
	}
	public void setBooks(Set<Book> books) {
		this.books = books;
	}
	@Override
	public String toString() {
		return "Category [categoryId=" + categoryId + ", categoryName=" + categoryName + "]";
	}
	
}

多对多的查询

public Category getCategory(Category category) {
		Session session = SessionFactoryUtils.openSession();
		Transaction transaction = session.beginTransaction();
		Category c = session.get(Category.class, category.getCategoryId());
		transaction.commit();
		session.close();
		return c;
	}
	
	public Book getBook(Book book) {
		Session session = SessionFactoryUtils.openSession();
		Transaction transaction = session.beginTransaction();
		Book b = session.get(Book.class, book.getBookId());
		if (b != null && new Integer(1).equals(book.getInitCategories())) {
			Hibernate.initialize(b.getCategories());
		}
		transaction.commit();
		session.close();
		return b;
	}

	@Test
	public void testGetBook() {
		Book book = new Book();
		book.setBookId(3);
		book.setInitCategories(1);
		Book b = this.bookDao.getBook(book );
		System.out.println(b.getBookName());
		System.out.println(b.getCategories());
	}

多对多的新增（inverse属性详解)

public Integer addBook(Book book) {
		Session session = SessionFactoryUtils.openSession();
		Transaction transaction = session.beginTransaction();
		Integer bid = (Integer) session.save(book);
		transaction.commit();
		session.close();
		return bid;
	}
	
	public Integer addCategory(Category category) {
		Session session = SessionFactoryUtils.openSession();
		Transaction transaction = session.beginTransaction();
		Integer cid = (Integer) session.save(category);
		transaction.commit();
		session.close();
		return cid;
	}

	/**
	 * book.hbm.xml	inverse=fasle
	 * category.hbm.xml inverse=true
	 * 数据添加正常
	 * 书籍表、桥接表各新增一条数据
	 */
	@Test
	public void test1() {
		Book book = new Book();
		book.setBookName("⭐先打我队友");
		book.setPrice(10f);
		Category category = new Category();
		category.setCategoryId(2);
//		直接将category对象加入到新建的book中是错误的，因为此时的category是临时态的，hibernate是不会管理的
//		book.getCategories().add(category);
		Category c = this.bookDao.getCategory(category);
		
//		c.getBooks().add(book);
		book.getCategories().add(c);
		this.bookDao.addBook(book);
	}

	/**
	 * book.hbm.xml	inverse=true
	 * category.hbm.xml inverse=true
	 * 只增加书籍表数据
	 * 桥接表不加数据
	 * 原因：双方都没有去维护关系
	 */
	@Test
	public void test2() {
		Book book = new Book();
		book.setBookName("哈嘎滑稽");
		book.setPrice(10f);
		Category category = new Category();
		category.setCategoryId(5);
		Category c = this.bookDao.getCategory(category);
		
		book.getCategories().add(c);
		this.bookDao.addBook(book);
//		c.getBooks().add(book);
	}

	/**
	 * inverse进一步讲解
	 */
	@Test
	public void test3() {
		Category category = new Category();
		category.setCategoryName("4");
		Book book = new Book();
		book.setBookId(3);
		Book b = bookDao.getBook(book);
		category.getBooks().add(b);
		this.bookDao.addCategory(category);
		
	}
	

 cascade="save-update" inverse="false"

cascade级联操作
cascade表示级联操作，即两个实体间存在级联关系（一个类是另一个类中的属性）时，当保存、更新或删除一个实体时，是否对关联的实体做出相应操作（数据操作）。

在hibernate中，通过session.save方法保存一个持久化对象这种方式称为显示保存

inverse标签属性:
inverse:外键维护，默认为false。代表一方不去维护多方外键。（inverse有反转的意思）
外键属于谁, 谁就负责维护.

用于指示本方是否参与维护关系，设置为true表示不维护，设置false表示维护，默认为false。
本属性一般用于一对多关系中一端，并设置为false。因为若由一端负责维护，每次更新完一端数据，都会去寻找与一端有关系的多端表中的行，并更新其外键字段。而多端维护时，由于一端对象是多端对象的属性字段，所以，每次更新多端后提交数据，都会自动更新该字段（若有更新时），这样比较方便。

多对多的级联删除（慎用，会将三张表的数据清空）

public void delBook(Book book) {
		Session session = SessionFactoryUtils.openSession();
		Transaction transaction = session.beginTransaction();
		session.delete(book);
		transaction.commit();
		session.close();
	}
	
	public void delCategory(Category category) {
		Session session = SessionFactoryUtils.openSession();
		Transaction transaction = session.beginTransaction();
		Category c = session.get(Category.class, category.getCategoryId());
		if(c!=null) {
			for (Book b : c.getBooks()) {
//				通过在被控方通过主控方来解除关联关系，最后被控方再做删除
				b.getCategories().remove(c);
			}
		}
		session.delete(c);
		transaction.commit();
		session.close();
	}

/**
	 * 书籍为主控方
	 */
	@Test
	public void test4() {
		Book book = new Book();
		book.setBookId(1);
		this.bookDao.delBook(book);
	}
	
	@Test
	public void test5() {
		Category category = new Category();
		category.setCategoryId(1);
		this.bookDao.delCategory(category);
	}

注意的地方:

​ 非级联删除只会删除正向多方数据库表和中间关系表中的记录，不会删除反向多方表中的记录

​ 级联删除既会删除正向多方数据库表中的记录，也会删除反向多方表中的记录和中间关系表中的记录

。。。。。