Hibernate学习⑤：多对多
一、数据库的多对多
1、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
注意：
①数据库多表联接查询
永远就是二个表的联接查询
②交叉连接
③外连接：left(左)/right(右)/full(左右)
主从表：连接条件不成立时，主表记录永远保留，与null匹配
说明：
在hibernate中，只管查询当前表对象即可，因为hibernate会自动关联桥表 以及关联表查询出关联对象
菜单案例：
entity：TreeNode
package com.zking.five.entity;
import java.util.ArrayList;
import java.util.HashSet;
import java.util.List;
import java.util.Set;
public class TreeNode {
private Integer treeNodeId;
private String treeNodename;
private Integer treeNodeType;
private Integer posotion;
private String url;
// 两种关系:
// ①当前节点与子节点的关联关系 一对多
// private Set<TreeNode> children = new HashSet<TreeNode>();
private List<TreeNode> children = new ArrayList<TreeNode>();
// ②当前节点与父节点的关系 多对一
private TreeNode parent;
private Integer initChild;
public Integer getTreeNodeId() {
return treeNodeId;
}
public void setTreeNodeId(Integer treeNodeId) {
this.treeNodeId = treeNodeId;
}
public String getTreeNodename() {
return treeNodename;
}
public void setTreeNodename(String treeNodename) {
this.treeNodename = treeNodename;
}
public Integer getTreeNodeType() {
return treeNodeType;
}
public void setTreeNodeType(Integer treeNodeType) {
this.treeNodeType = treeNodeType;
}
public Integer getPosotion() {
return posotion;
}
public void setPosotion(Integer posotion) {
this.posotion = posotion;
}
public String getUrl() {
return url;
}
public void setUrl(String url) {
this.url = url;
}
public List<TreeNode> getChildren() {
return children;
}
public void setChildren(List<TreeNode> children) {
this.children = children;
}
public TreeNode getParent() {
return parent;
}
public void setParent(TreeNode parent) {
this.parent = parent;
}
public Integer getInitChild() {
return initChild;
}
public void setInitChild(Integer initChild) {
this.initChild = initChild;
}
@Override
public String toString() {
return "TreeNode [treeNodeId=" + treeNodeId + ", treeNodename=" + treeNodename + ", children=" + children + "]";
}
}
*.hbm.xml：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 table = "t_hibernate_sys_tree_node" name = "com.zking.five.entity.TreeNode">
<id name = "treeNodeId" type = "java.lang.Integer" column = "tree_node_id">
<generator class="increment"></generator>
</id>
<property name = "treeNodename" type = "java.lang.String" column = "tree_node_name"></property>
<property name = "treeNodeType" type = "java.lang.Integer" column = "tree_node_type"></property>
<property name = "posotion" type = "java.lang.Integer" column = "position"></property>
<property name = "url" type = "java.lang.String" column = "url"></property>
<!-- <set name = "children" cascade="save-update" inverse="true">
<key column = "parent_node_id"></key>
<one-to-many class = "com.zking.five.entity.TreeNode"></one-to-many>
</set> -->
<!-- order-by数据库中的表字段 -->
<bag order-by="position" name = "children" cascade="save-update" inverse="true">
<key column = "parent_node_id"></key>
<one-to-many class = "com.zking.five.entity.TreeNode"></one-to-many>
</bag>
<many-to-one name = "parent" class = "com.zking.five.entity.TreeNode" column = "parent_node_id"></many-to-one>
</class>
</hibernate-mapping>
dao ： TreeNodeDao
package com.zking.five.dao;
import org.hibernate.Hibernate;
import org.hibernate.Session;
import org.hibernate.Transaction;
import com.zking.five.entity.TreeNode;
import com.zking.two.util.SessionFactoryUtils;
public class TreeNodeDao {
//查看
public TreeNode get(TreeNode treeNode) {
Session session = SessionFactoryUtils.getSession();
Transaction transaction = session.beginTransaction();
TreeNode tn = session.get(TreeNode.class, treeNode.getTreeNodeId());
if(tn != null && new Integer(1).equals(treeNode.getInitChild())) {
Hibernate.initialize(tn.getChildren());
}
// System.out.println(tn);
transaction.commit();
session.close();
return tn;
}
}
测试 ： TreeNodeDaoTest
package com.zking.five.dao;
import static org.junit.Assert.*;
import org.junit.Before;
import org.junit.Test;
import com.zking.five.entity.TreeNode;
public class TreeNodeDaoTest {
private TreeNodeDao treeNodeDao = new TreeNodeDao();
@Before
public void setUp() throws Exception {
}
@Test
public void testGet() {
TreeNode treeNode = new TreeNode();
treeNode.setTreeNodeId(1);
treeNode.setInitChild(1);
TreeNode tn = this.treeNodeDao.get(treeNode);
/*根据id直接打印一级节点以及其所有子节点
System.out.println(tn);
* 会报错
failed to lazily initialize a collection of role:
com.zking.five.entity.TreeNode.children,
could not initialize proxy - no Session
* 代码分析：
System.out.println(tn.getTreeNodeId()+" , "+tn.getTreeNodename());
for (TreeNode tn2 : tn.getChildren()) {
System.out.println(tn2.getTreeNodeId()+" , "+tn.getTreeNodename());
}
*
* 原理分析：
* 当加载以及节点的时候没问题
* 加载二级节点的时候，由于设置了强制加载，同样可以加载所有的二级节点。没问题
* 加载三级节点，这时session关闭了，并且默认查出来的节点默认采用懒加载
*
* 权限菜单加载的两种方式：
* 1、一次性将数据库表中的数据全部加载往浏览器返回（是用于菜单较少）
* 2、菜单表数据较大，当浏览器出现卡顿的情况，第一中情况不再使用
* 那么就采用逐级加载。——逐级加载事件（异步）
*
*/
System.out.println(tn.getTreeNodeId()+" , "+tn.getTreeNodename());
for (TreeNode tn2 : tn.getChildren()) {
System.out.println(tn2.getTreeNodeId()+" , "+tn.getTreeNodename());
}
}
}
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
①一定要定义一个主控方
② 多对多删除
（1）主控方直接删除
（2）被控方先通过主控方解除多对多关系，再删除被控方
（3）禁用级联删除
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
书籍与其书书籍类型案例
entity：book
package com.zking.five.entity;
import java.util.HashSet;
import java.util.Set;
public class Book {
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 Set<Category> getCategories() {
return categories;
}
public void setCategories(Set<Category> categories) {
this.categories = categories;
}
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;
}
}
entity : Category
package com.zking.five.entity;
import java.util.HashSet;
import java.util.Set;
public class Category {
private Integer categoryId;
private String categoryName;
private Set<Book> books = new HashSet<Book>();
private Integer initBooks = 0;
public Integer getInitBooks() {
return initBooks;
}
public void setInitBooks(Integer initBooks) {
this.initBooks = initBooks;
}
public Set<Book> getBooks() {
return books;
}
public void setBooks(Set<Book> books) {
this.books = books;
}
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;
}
}
*.hbm.xml : 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 table = "t_hibernate_book" name = "com.zking.five.entity.Book">
<id name = "bookId" type = "java.lang.Integer" column = "book_id">
<generator class="increment"></generator>
</id>
<property name = "bookName" type = "java.lang.String" column = "book_name"></property>
<property name = "price" type = "java.lang.Float" column = "price"></property>
<!--
table：桥接表
-->
<set table="t_hibernate_book_category" name = "categories" cascade="delete" inverse="false">
<!-- 当前类对应的表主键在桥接表的外键 -->
<key column = "bid"></key>
<many-to-many column = "cid" class = "com.zking.five.entity.Category"></many-to-many>
</set>
</class>
</hibernate-mapping>
*.hbm.xml : 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 table = "t_hibernate_category" name = "com.zking.five.entity.Category">
<id name = "categoryId" type = "java.lang.Integer" column = "category_id">
<generator class="increment"></generator>
</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.zking.five.entity.Book"></many-to-many>
</set>
</class>
</hibernate-mapping>
dao : BookDao
package com.zking.five.dao;
import java.io.Serializable;
import org.hibernate.Hibernate;
import org.hibernate.Session;
import org.hibernate.Transaction;
import com.zking.five.entity.Book;
import com.zking.two.util.SessionFactoryUtils;
public class BookDao {
public Book get(Book book) {
Session session = SessionFactoryUtils.getSession();
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;
}
// *************************six**************************************************//
public Integer add(Book book) {
Session session = SessionFactoryUtils.getSession();
Transaction transaction = session.beginTransaction();
Integer bid = (Integer) session.save(book);
transaction.commit();
session.close();
return bid;
}
public void del(Book book) {
Session session = SessionFactoryUtils.getSession();
Transaction transaction = session.beginTransaction();
session.delete(book);
transaction.commit();
session.close();
}
}
dao： Categorydao
package com.zking.five.dao;
import org.hibernate.Hibernate;
import org.hibernate.Session;
import org.hibernate.Transaction;
import com.zking.five.entity.Book;
import com.zking.five.entity.Category;
import com.zking.two.util.SessionFactoryUtils;
public class Categorydao {
public Category get(Category category) {
Session session = SessionFactoryUtils.getSession();
Transaction transaction = session.beginTransaction();
Category c = session.get(Category.class, category.getCategoryId());
if(c != null && new Integer(1).equals(category.getInitBooks())) {
Hibernate.initialize(c.getBooks());
}
transaction.commit();
session.close();
return c;
}
// *************************six**************************************************//
public Integer add(Category category) {
Session session = SessionFactoryUtils.getSession();
Transaction transaction = session.beginTransaction();
Integer cid = (Integer) session.save(category);
transaction.commit();
session.close();
return cid;
}
/*
* 被控方删除
* 1、被控方通过主控关系解除关联关系
* 2、在去删除被控方
*/
public void del(Category category) {
Session session = SessionFactoryUtils.getSession();
Transaction transaction = session.beginTransaction();
Category c = session.get(Category.class, category.getCategoryId());
for (Book b : c.getBooks()) {
// c.getBooks().remove(b);
b.getCategories().remove(c);
}
session.delete(c);
transaction.commit();
session.close();
}
}
测试：BookDaoTest
package com.zking.five.dao;
import static org.junit.Assert.*;
import org.junit.Before;
import org.junit.Test;
import com.zking.five.entity.Book;
import com.zking.five.entity.Category;
public class BookDaoTest {
private BookDao bookDao = new BookDao();
private Categorydao categorydao = new Categorydao();
@Before
public void setUp() throws Exception {
}
/**
* 通过一本能过查询到多个类别
* jdbc:三表联差
* hibernate:只需要查询单个对象即可，它会自动关联查询，交给映射文件即可
*/
@Test
public void testGet1() {
Book book = new Book();
book.setBookId(5);
book.setInitCategories(1);
Book b = this.bookDao.get(book);
System.out.println(b.getBookName());
for (Category c : b.getCategories()) {
System.out.println(c.getCategoryName());
}
/*
* 《悲伤逆流成河》
情感
发牢骚
青春
*/
}
/**
* 查询同一类别下的所有书籍
*/
@Test
public void testGet2() {
Category category = new Category();
category.setCategoryId(1);
category.setInitBooks(1);
Category c = this.categorydao.get(category);
System.out.println(c.getCategoryName());
for (Book b : c.getBooks()) {
System.out.println(b.getBookName());
}
/*
* 情感
《悲伤逆流成河》
《爸爸妈妈》
《论辈分，论年龄》
*/
}
// *************************six**************************************************//
/**
* 级联新增
* book.hbm.xml :inverse = false
* category.hbm.xml:inverse = true
* 含义：将级联关系的维护责任交给book对象
*
*
* jdbc:
* this.bookDao.add
* this.bookCategoryDao.add
*
* hibernate:
* this.bookDao.add
*
* 注意：在多对多的关系维护中，hibernate管理的是持久态对象
*/
@Test
public void testAdd1() {
Book book = new Book();
book.setBookName("《霸道总裁爱上我222》");
book.setPrice(123f);
// new 一个对象 临时态对象
Category category = new Category();
category.setCategoryId(6);
/**
* 会报错
*/
// book.getCategories().add(category)
book.getCategories().add(this.categorydao.get(category));
this.bookDao.add(book);
}
/**
* 添加一个新的类别，绑定原有的某个书籍
*/
@Test
public void testAdd2() {
Category category = new Category();
category.setCategoryName("惊悚");
Book book = new Book();
book.setBookId(6);
category.getBooks().add(this.bookDao.get(book));
this.categorydao.add(category);
}
/**
* book.hbm.xml :inverse = true
* category.hbm.xml:inverse = true
* 双方关系各不维护
*/
@Test
public void testAdd3() {
Category category = new Category();
category.setCategoryName("惊悚1");
Book book = new Book();
book.setBookId(6);
category.getBooks().add(this.bookDao.get(book));
this.categorydao.add(category);
}
/**
* 主控方删除
* 需求：删除有关联关系的一本书
*
* jdbc:
* this.bookCategoryDao.delete
* this.bookDao.delete
*
* hibernate：
* this.bookDao.delete
*/
@Test
public void testDel1(){
Book book = new Book();
book.setBookId(8);
this.bookDao.del(book);
}
/**
* 被控方删除
* 需求：删除有关联关系的一个类别包括该类别下的所有数据
*
*/
@Test
public void testDel2(){
Category category = new Category();
category.setCategoryId(3);
this.categorydao.del(category);
}
}