Hibernate 一对多自关联 多对多

转载 于 2019-07-17 19:58:00 发布 · 74 阅读 · 0 ·
CC 4.0 BY-SA版权
原文链接：http://www.cnblogs.com/chenjiahao9527/p/11203293.html
文章标签：

#java #数据库

本文介绍了一对多自关联及多对多关联在Hibernate中的实现方式，包括实体类设计、XML配置、DAO层操作及测试代码。涵盖树形结构的自关联实现和多对多关联的双向维护。

一对多自关联（说白了就是自己关联自己）比如：

商城里面的分类，一级分类：电器，家具等等。

           电器下面分二级分类：厨房电器，生活电器等等。

           二级分类厨房电器下的三级分类：电压力锅，电磁炉等等。。   

数据库：

实体类：（TreeNode）

 

package com.chenjiahao.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懒加载 1、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 + "]";
}
}

 

　　

 

　　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.chenjiahao.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.chenjiahao.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.chenjiahao.four.entity.TreeNode"/>
		</set>
	</class>
</hibernate-mapping>

 

　　


在主配置文件/hibernate.cfg.xml中加：

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

　　TreeNodeDao层

package com.chenjiahao.four.dao;

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

import com.chenjiahao.four.entity.TreeNode;
import com.chenjiahao.two.util.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;
	}
}

　　

TreeNodeDaoTest测试：

package com.chenjiahao.four.dao;

import org.junit.Test;

import com.chenjiahao.four.entity.TreeNode;




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

//	@Before
//	public void setUp() throws Exception {
//	}
//
//	@After
//	public void tearDown() throws Exception {
//	}

	@Test
	public void testLoad() {
		TreeNode treeNode = new TreeNode();
		treeNode.setNodeId(6);
		treeNode.setInitChildren(1);
		
		TreeNode t = this.treeNodeDao.load(treeNode);
		//拿到当前节点
		System.out.println(t);
		//拿到当前节点的父节点
		System.out.println(t.getParent());
		//拿到当前节点的 子节点
		System.out.println(t.getChildren());
	}

}

　　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     

书本表：t_hibernate_book;
书本类别表：t_hibernate_category;
中间表： t_hibernate_book_category;

 

t_hibernate_book;

t_hibernate_category;

t_hibernate_book_category

实体类和xml配置：

Book:

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;
}

　　Category:

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>();
}

 incerse在下面book.hbm.xml和Category.hbm.xml里面都体现了，incerse主要是维护中间表。

  book.hbm.xml inverse=false
  category.hbm.xml inverse=false
  数据添加正常
  书籍表、书籍类别关联表各新增一条数据

 

  book.hbm.xml inverse=true
  category.hbm.xml inverse=true
  只增加书籍表数据
  书籍类别关联表不加数据
  原因：双方都没有去维护关系



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.chenjiahao.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="false">
			<key column="cid"></key>
			<many-to-many column="bid" class="com.chenjiahao.four.entity.Book"></many-to-many>
		</set>
	</class>
</hibernate-mapping>

　　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.chenjiahao.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)中的外键bid
		     many-to-many：
		             column：对应的是上面key查出来中间表(t_hibernate_book_category)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
		     流程：
		     以查询book_id=1西游记这本书为例
		     1、通过建模反射自动生成sql，可以拿到book_id这条记录的基本信息{book_id=1,book_name=西游记,book_price=50}
		     2、book_id=1->bid=1去查询中间表t_hibernate_book_category，拿到了cid=1,2
		     3、cid=1,2->t_hibernate_category的category_id=1,2
		     4、拿到当前book实列对应的categroy的集合
		     5、最终{book_id=1,book_name=西游记,book_price=50}->
		     {book_id=1,book_name=西游记,book_price=50,category=[categoryId=2, categoryName=神话], Category [categoryId=1, categoryName=古典]]}
		 -->
		<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.chenjiahao.four.entity.Category"></many-to-many>
		</set>
	</class>
</hibernate-mapping>

　　在主配置文件/hibernate.cfg.xml中加：

<!-- 多对多的自关联 -->
        <mapping resource="com/chenjiahao/four/entity/Book.hbm.xml"/>
        <mapping resource="com/chenjiahao/four/entity/Category.hbm.xml"/

 

dao层：

package com.chenjiahao.four.dao;

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

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

import com.chenjiahao.four.entity.Book;
import com.chenjiahao.four.entity.Category;
import com.chenjiahao.two.util.SessionFactoryUtils;


import antlr.StringUtils;

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：

package com.chenjiahao.four.dao;

import org.junit.Test;

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

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

	@Test
	public void testGetBook() {
		Book book = new Book();
		book.setBookId(1);
		book.setInitCategories(1);
		Book b = this.bookDao.getBook(book );
		System.out.println(b.getBookName());
		System.out.println(b.getCategories());
	}
	
	/**
	 * book.hbm.xml	inverse=false
	 * 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("00咖啡店说课稿5");
		book.setPrice(10f);
		Category category = new Category();
		category.setCategoryId(1);
//		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);
		//将数据库里面的类别数据查找出来
		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("斗宗强者");
		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);
	}
	
	
}

　　

 

　　

 

转载于:https://www.cnblogs.com/chenjiahao9527/p/11203293.html

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