hibernate 多对多关联关系

1.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

2. 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)

3 多对多关系注意事项

一定要定义一个主控方

多对多删除

主控方直接删除

被控方先通过主控方解除多对多关系，再删除被控方

禁用级联删除

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

添加实体类及配置文件：

Book 

package com.hxc.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();
    }
    
    
}

 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.hxc.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：是对应的中间表        没有实体类，意味着两张主表对应的映射联合管理数据
                name:当前映射文件对应的实体类对应的属性
                cascade：级联新增修改，说白了就是当前实体类对应的表删除是否能够影响到关联表的数据
                inverse:中间表的数据维护的权力交给对方
            key：标签：
                column：当前表t_hibernate_book的主键book_id在中间表的列段bid
            many-to-many:
                column|:代表中间表对应的除去当前表t_hibernate_book的非主键的中间表的cid
                class：cid对应的类
         -->
        
        <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.hxc.four.entity.Category"></many-to-many>
        </set>
    </class>
</hibernate-mapping>

 Category 

package com.hxc.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 + "]";
    }
    
}

 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.hxc.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.hxc.four.entity.Book"></many-to-many>
        </set>
    </class>
</hibernate-mapping>

TreeNode 

package com.hxc.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 + ", initChildren=" + initChildren + "]";
    }

    

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

    
    

}

treeNode.hxm.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.hxc.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.hxc.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.hxc.four.entity.TreeNode"/>
        </set>
    </class>
</hibernate-mapping>

 hibernate.cfg.xml

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE hibernate-configuration PUBLIC
    "-//Hibernate/Hibernate Configuration DTD 3.0//EN"
    "http://www.hibernate.org/dtd/hibernate-configuration-3.0.dtd">
<hibernate-configuration>
    <session-factory>
        <!-- 1. 数据库相关 -->
        <property name="connection.username">root</property>
        <property name="connection.password">123</property>
        <property name="connection.url">jdbc:mysql://localhost:3306/mytable?useUnicode=true&amp;characterEncoding=UTF-8
        </property>
        <property name="connection.driver_class">com.mysql.jdbc.Driver</property>
        <property name="dialect">org.hibernate.dialect.MySQLDialect</property>

        <!-- 配置本地事务（No CurrentSessionContext configured!） -->
        <property name="hibernate.current_session_context_class">thread</property>

        <!-- 2. 调试相关 -->
        <property name="show_sql">true</property>
        <property name="format_sql">true</property>

        <!-- 3. 添加实体映射文件 -->
        <mapping resource="com/hxc/one/entity/user.hbm.xml" />
        <!-- 主键生成策略 -->
        <mapping resource="com/hxc/two/entity/Student.hbm.xml"/>
        <mapping resource="com/hxc/two/entity/Worker.hbm.xml"/>
        <!-- 一对多关联关系 -->
        <mapping resource="com/hxc/three/entity/Order.hbm.xml"/>
        <mapping resource="com/hxc/three/entity/OrderItem.hbm.xml"/>
        <!-- 一对多自关联 -->
        <mapping resource="com/hxc/four/entity/TreeNode.hbm.xml"/>        
        <!-- 多对多关联 -->
        <mapping resource="com/hxc/four/entity/Book.hbm.xml"/>        
        <mapping resource="com/hxc/four/entity/Category.hbm.xml"/>        
        
    </session-factory>
</hibernate-configuration>        

BookDao

package com.hxc.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.hxc.four.entity.Book;
import com.hxc.four.entity.Category;
import com.hxc.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();
    }
    
    
}

BookDao:

package com.hxc.four.dao;

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

import com.hxc.four.entity.TreeNode;
import com.hxc.two.util.SessionFactoryUtils;

public class TreeNodeDao {
    public TreeNode load(TreeNode treeNode) {
        Session session = SessionFactoryUtils.openSession();
        System.out.println(session);
        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;
    }
}

BookDaoTest

package com.hxc.four.dao;

import org.junit.Test;

import com.hxc.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);
        System.out.println(t);
        System.out.println(t.getParent());
        System.out.println(t.getChildren());
    }

}

运行BookDaoTest：


运行 BookDaoTest中的getBook：