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Hibernate关联关系（多对多）

由 怎甘沉沦 提交于 2019-11-29 04:20:23

Hibernate关联关系（多对多）

一. 自关联查询

自关联查询就是自己充当多方
同时也充当一方 即多和一都在同一张表中
一般这样的表其实可以看做是一个树形结构 在数据库表中有一个外键
该外键表示当前数据的父节点

案例:

一对多的自关联

数据库表如下：

在这里插入图片描述
实体类TreeNode.java

package com.xwt.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;

		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 + "]";
		}	
	}

配置文件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.xwt.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.xwt.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.xwt.four.entity.TreeNode"/>
		</set>
	</class>
</hibernate-mapping>

配置hibernate.cfg.xml

<!-- 一对多的自关联  -->
<mapping resource="com/xwt/four/entity/TreeNode.hbm.xml"/>

Dao方法TreeNodeDao.java

package com.xwt.four.dao;

import org.hibernate.Hibernate;
import org.hibernate.Session;
import org.hibernate.Transaction;

import com.xwt.four.entity.TreeNode;
import com.xwt.two.uity.SessionFactoryUtils;

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;
	}
}

测试类TreeNodeDaoTest.java

package com.xwt.four.dao;

import org.junit.Test;

import com.xwt.four.entity.TreeNode;

public class TreeNodeDaoTest {
	private TreeNodeDao treeNodeDao = new TreeNodeDao();

	/**
	 *   注意:它只能加载出直系亲属（父节点和子节点）
	 */
	@Test
	public void testLoad() {
		TreeNode treeNode = new TreeNode();
		//权限管理
		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());
	}
}

结果
在这里插入图片描述

二.Hibernate的多对多

  1. hibernate可以直接映射多对多关联关系(看作两个一对多)
  2. 多对多关系注意事项
    2.1 一定要定义一个主控方
    2.2 多对多删除
    2.2.1 主控方直接删除
    2.2.2 被控方先通过主控方解除多对多关系，再删除被控方
    2.2.3 禁用级联删除
    2.3 关联关系编辑，不需要直接操作桥接表，hibernate的主控方会自动维护

案例：

多对多级联查询

实体类Book.java

package com.xwt.four.entity;

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

public class Book implements Serializable{
	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();
	}	
}

Category.java

package com.xwt.four.entity;

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

public class Category implements Serializable{
	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 + "]";
	}
	
}

配置文件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.xwt.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>
		<!-- 
		        set标签
		                     table:指的是中间表
		                     name:指的是实体类中的关联属性
		                     cascade:级联新增以及级联修改
		                     inverse:中间表的数据维护交给那个实体类来控制 inverse的字面意思是反方
		                                     默认inverse=true  那意味着 默认由对方来控制中间表数据的维护
		                                     
		       key标签
		                   column:代表当前映射类Book对应的表t_hibernate_book的主键  在中间表的外键
		                  
		       many-to-many标签
		                    column:当前映射类关联属性对应的类的主键  在中间表的外键
		                    class:当前映射类关联属性对应的类的全路径名
		  -->
		<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.xwt.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>
    <!--  hibernate中多对多的查询原理：
				1、建模得到sessionfactory工厂
				2、sessionfactory中包含两个多对多关系映射文件，
				那么就可以通过流加载那两个映射文件，
				这里以	"com/xwt/four/entity/category.hbm.xml"为例，
				加载完后可以对其建模
				3、可以拿到"com/xwt/four/entity/category.hbm.xml" 以及表t_hibernate_category
				通过t_hibernate_category以及下列的column列段可以动态生成sql语句
				select category_id,category_name from t_hibernate_category where category_id=?(假设 5)
				那么可以查询到结果 5 a1
				反射实例化：
				Category c = Class.forName("com/xwt/four/entity/category.hbm.xml")
				Field categoryNameField = c.getClass().getDecafiedld("categoryName")
				categoryNameField.setAccessable(true);打开权限
				categoryNameField.set(c,"a1");
				同理可以设置属性：
				categoryNameField.set(c,5);
				那也就意味着当前c实例中所有属性值已经赋值完毕
				
				4、同样对此文件com/xwt/four/entity/category.hbm.xml建模可以得到
				中间表 t_hibernate_book_category
				以及关联属性的全路径名com.xwt.four.entity.Book
				自然形成一个sql语句：
				select bid,cid from t_hibernate_book_category where cid=?(假设 5)
				查询结果：5	17	5
					  	 6	20	5
						……
				select * from t_hibernate_book where book_id in (17,20...)		
				BaseDao.executeQuery（sql，Class clz，pagebean）	
				List<book> books = BaseDao.executeQuery（sql，Book.class，null）		
				
				5、给关联属性赋值
				 c.setBooks(books) 
           -->
	<class name="com.xwt.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.xwt.four.entity.Book"></many-to-many>
		</set>
	</class>
</hibernate-mapping>

配置hibernate.cfg.xml

<!-- 多对多的讲解  -->
<mapping resource="com/xwt/four/entity/book.hbm.xml"/>
<mapping resource="com/xwt/four/entity/category.hbm.xml"/>

Dao方法BookDao.java

package com.xwt.four.dao;

import org.hibernate.Hibernate;
import org.hibernate.Session;
import org.hibernate.Transaction;

import com.xwt.four.entity.Book;
import com.xwt.four.entity.Category;
import com.xwt.two.uity.SessionFactoryUtils;

public class BookDao{
	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;
	}
	
	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;
	}
	
	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();
	}	
}

测试类BookDaoTest.java

package com.xwt.four.dao;

import org.junit.Test;

import com.xwt.four.entity.Book;
import com.xwt.four.entity.Category;

public class BookDaoTest {
	private BookDao bookDao = new BookDao();

	@Test
	public void testGetBook() {
		Book book = new Book();
		book.setBookId(8);
		book.setInitCategories(1);
		Book b = this.bookDao.getBook(book );
		System.out.println(b.getBookName());
		System.out.println(b.getCategories());
	}
	
	/**
	 * 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("李翔渣男");
		book.setPrice(10f);
		Category category = new Category();
		category.setCategoryId(8);
        //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("c");
		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);
	}	
}
标签
关联关系
外键
hibernate
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