查看java类关联关系

Hibernate （关联关系）多对多

一对多的自关联

得到 Tree 的父节点 和字节点

TreeNode 实体类:上对数据库进行描述

package com.hyf.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; 
	
 //  set/get  toString 方法省略  
}

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

配置事务

一对多的自关联

<mapping resource="com/hyf/four/entity/TreeNode.hbm.xml"/>

dao 方法

package com.hyf.four.dao;

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

import com.hyf.four.entity.TreeNode;
import com.hyf.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;
	}
}

Junit 测试

package com.hyf.four.dao;
import org.junit.Test;
import com.hyf.four.entity.TreeNode;

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

	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());
	}

}

控制台输出

---

多对多

数据库表

书籍表 t_hibernate_book

中间表 t_hibernate_book_category

书籍类别表 t_hibernate_category

实体类
中间表不需要实体类(t_hibernate_book_category)

Book.java

package com.hyf.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;
	
	//  set/get toString 有参 无参 构造方法  省略
}

Category.java

package com.hyf.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>();
	
		//  set/get toString 有参 无参 构造方法  省略

映射文件
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.hyf.four.entity.Book" table="t_hibernate_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    : 指的是实体类属性
		      cascade : 级联新增以及修改
		      inverse : 中间表的数据交给那个实体类控制,inverse 的意思是反方默认 inverse=true
		                                          意味着，默认有对方来控制中间表数据维护
		    key标签     
		      column  : 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.hyf.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.hyf.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.hyf.four.entity.Book"></many-to-many>
		</set>
	</class>
</hibernate-mapping>

配置事务

<!--7.多对多  -->
		<mapping resource="com/hyf/four/entity/book.hbm.xml"/>
		<mapping resource="com/hyf/four/entity/category.hbm.xml"/>

dao 方法

package com.hyf.four.dao;


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

import com.hyf.four.entity.Book;
import com.hyf.four.entity.Category;
import com.hyf.two.util.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();
	}
	
	
}

级联新增 inverse属性值的设置

Junit 测试

1. 当维护方为 book

/**
	 * book.hbm.xml	inverse=fasle
	 * category.hbm.xml inverse=true
	 * 数据添加正常
	 * 书籍表、中间表各新增一条数据
	 */
	@Test
	public void test1() {
		Book book = new Book();
		book.setBookName("鬼谷子2");
		book.setPrice(19f);
		Category category = new Category();
		category.setCategoryId(5);
//		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);
	}

书籍表 t_hibernate_book 和 中间表 t_hibernate_book_category 各加一行数据

2. 双方都不 维护

/**
	 * 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);
	}

运行结果：
书籍表 t_hibernate_book 加了一条数据 中间表没有加

Hibernate 多对多底层原理

Hibernate 中多对多原理，

• 1、建模得到sessionfactory 工厂
• 2、sessionfactory中包含了两个多对多的映射文件，那么就可以通过流加载那两个映射文件
  这里com/hyf/four/entity/category.hbm.xml 加载完毕后可以对其建模
• 3、可以拿到 com.zking.four,entity.Category以及表t_hibernate_category
  通过 t_hibernate_category以及下列column以及列段可以多态生产sql语句
  select category_id, categoryName from t_hibernate_category where category_id=?
  假设查询结果为：5 a1
  Category c =Class.forName(com.hyf.four.entity.Category);
  Filed categoryFiled =c.getClass().getDecafiedld(“categoryName”)
  categoryNameField.setAccessable(true); // 打开访问权限
  categoryNameField.set(c,“a1”)
  同理
  categoryNameField.set(c,“5”)
  那也意味着当前c实例中所有属性值已经赋值完毕
• 4、 通用对此com/hyf/four/entity/category.hbm.xml文件建模 ，可以的到
  中间表t_hibernate_book_category
  以及关联属性全路径名com.hyf.four.entity.Book
  自然形成一个sql语句
  select cid,bid from t_hibernate_book_category where cid=(5)
  String sql= select * from t_hibernate_book where book_id in(xxxx)
  BaseDao.executeQuery(sql,Book.class,null);
• 5 、c.setBooks(books)