hibernate：多对多
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2022-04-14 21:49:46
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1. 数据库的多对多
1.1 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1：数据库多表联接查询
永远就是二个表的联接查询
A B C D
t1 C
t2 D
t3
注2：交叉连接
注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
A B AB
select * from A,B,AB WHERE A.aID=AB.aID and b.bid = AB.bid
where
在hibernate中，你只管查询当前表对象即可，
hibernate会自动关联桥表以及关联表查询出关联对象
Book Category Book_category
select * from Book b,Book_category bc,category where b.bid = bc.bid and bc.cid = c.cid
and bid = 2
2. hibernate的多对多
2.1 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
3.1 一定要定义一个主控方
3.2 多对多删除
3.2.1 主控方直接删除
3.2.2 被控方先通过主控方解除多对多关系，再删除被控方
3.2.3 禁用级联删除
3.3 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：
自关联查询 菜单表
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 position;
private String url;
//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>();
//当前节点与父节点的关系 多对一
private TreeNode parent;
private Integer initChildren;
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 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 List<TreeNode> getChildren() {
return children;
}
public void setChildren(List<TreeNode> children) {
this.children = children;
}
// public Set<TreeNode> getChildren() {
// return children;
// }
// public void setChildren(Set<TreeNode> children) {
// this.children = children;
// }
public TreeNode getParent() {
return parent;
}
public void setParent(TreeNode parent) {
this.parent = parent;
}
public Integer getInitChildren() {
return initChildren;
}
public void setInitChildren(Integer initChildren) {
this.initChildren = initChildren;
}
@Override
public String toString() {
return "TreeNode [treeNodeId=" + treeNodeId + ", treeNodeName=" + treeNodeName + ", treeNodeType="
+ treeNodeType + ", position=" + position + ", url=" + url + ", children=" + children + "]";
}
}
<?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="position" type="java.lang.Integer" column="position"></property>
<property name="url" type="java.lang.String" column="url"></property>
<!--
cascade：用来配置维护实体类之间的关系所用
inverse（反方，反转）：关系由反方控制
-->
<!-- <set name="children" cascade="save-update" inverse="true">
填外键
<key column="parent_node_id"></key>
<one-to-many class="com.zking.five.entity.TreeNode"></one-to-many>
</set> -->
<!-- order-by指的是数据库中的表字段 -->
<bag order-by="position" name="children" cascade="save-update" inverse="true">
<!-- 填外键 -->
<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>
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 {
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.getInitChildren())) {
Hibernate.initialize(tn.getChildren());
}
// System.out.println(tn);
transaction.commit();
session.close();
return tn;
}
}
package com.zking.five.dao;
import static org.junit.Assert.*;
import org.junit.Test;
import com.zking.five.entity.TreeNode;
public class TreeNodeDaoTest {
private TreeNodeDao treeNodeDao=new TreeNodeDao();
@Test
public void testGet() {
TreeNode treeNode=new TreeNode();
treeNode.setTreeNodeId(1);
treeNode.setInitChildren(1);
TreeNode tn = this.treeNodeDao.get(treeNode);
System.out.println(tn.getTreeNodeId()+","+tn.getTreeNodeName());
for (TreeNode tn2 : tn.getChildren()) {
System.out.println(tn2.getTreeNodeId()+","+tn2.getTreeNodeName());
}
/**
* 当加载一级节点的时候没问题
* 当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
* 当加载三级节点的时候，session已经关闭了，并且默认查出来的节点是默认采用的是懒加载
*
*
* 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（适用于菜单较少的情况）
* 2、菜单表数据量较大，当出现浏览器卡顿的情况，第一种方式就不再使用，那么就采用菜单逐级加载
*
*/
}
}
多对多级联查询 书籍表、书籍类别表
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 initCategoies=0;
public Set<Category> getCategories() {
return categories;
}
public void setCategories(Set<Category> categories) {
this.categories = categories;
}
public Integer getInitCategoies() {
return initCategoies;
}
public void setInitCategoies(Integer initCategoies) {
this.initCategoies = initCategoies;
}
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;
}
}
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 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;
}
}
<?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>
<!--
sql语句形成讲解
session.get(Book.class,1);
select * from t_hibernate_book where bookId=?(1)
resultSet->
1 西游记 50
Book book=Class.forName("com.zking.five.entity.Book");
book.setBookId(1);
book.setBookName(西游记);
book.setPrice(50);
categores为什么有值？
1、当前实体类的映射文件找到set标签的table属性
select * from t_hibernate_book_category
2、继续读取配置文件，拿到set标签中的子标签的key的column属性(column填的是当前类对应表的主键在桥接表的外键)
select cid from t_hibernate_book_category where bid=?(bookId=1)
resultSet->
只会得到1,2
3、set标签中->many-to-many->class（找到相关联的类com.zking.five.entity.Category）
categoty.hbm.xml
select * from t_hibernate_category
4、利用桥接表查询出来的数据查询关联表
select * from t_hibernate_category where category_id in(1,2)
1 古典
2 神话
5、EntityBaseDao中的executeQuery方法，对result进行处理，最终返回
List<Category> categories=new ArrayList<>();
while(rs.next){
Category c=Class.forName("com.zking.five.entity.Category").newInstance()
c.set...
categories.add(c)
}
6、book.setCategories(categorise)
重量级框架（对sql语句极度的封装了，查单个对象可以把相关联的对象一起查出来）
耗性能
-->
<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><!--跨数据库的奥秘 -->
</id>
<property name="bookName" type="java.lang.String" column="book_name"></property>
<property name="price" type="java.lang.Float" column="price"></property>
<!--
cascade：用来配置维护实体类之间的关系所用
inverse（反方，反转）：关系由反方控制
-->
<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.zking.five.entity.Category"></many-to-many>
</set>
</class>
</hibernate-mapping>
<?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><!--跨数据库的奥秘 -->
</id>
<property name="categoryName" type="java.lang.String" column="category_name"></property>
<!-- 多对多关系的 inverse必须一个是false一个是true-->
<set table="t_hibernate_book_category" name="books" cascade="save-update" inverse="true">
<!-- 填外键 -->
<key column="cid"></key>
<many-to-many column="bid" class="com.zking.five.entity.Book"></many-to-many>
</set>
</class>
</hibernate-mapping>
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.TreeNode;
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.getInitCategoies())) {
Hibernate.initialize(b.getCategories());
}
transaction.commit();
session.close();
return b;
}
}
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;
}
}
package com.zking.five.dao;
import static org.junit.Assert.*;
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();
/*
* 通过一本书能够查到多个类别
* jdbc:三表联查
* 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 testGet() {
Book book=new Book();
book.setBookId(1);
book.setInitCategoies(1);
Book b = this.bookDao.get(book);
System.out.println(b.getBookName());
for (Category c : b.getCategories()) {
System.out.println(c.getCategoryName());
}
}
/**
* 通过一个类别查询多个书籍
*/
@Test
public void testGet2() {
Category category=new Category();
category.setCategoryId(2);
category.setInitBooks(1);
Category c = this.categoryDao.get(category);
System.out.println(c.getCategoryName());
for (Book b : c.getBooks()) {
System.out.println(b.getBookName());
}
}
}