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)
3. 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
一对多关联关系案例：
实体类
package com.huang.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 + "]";
}
}
配置实体映射文件
<?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.huang.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.huang.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.huang.four.entity.TreeNode"/>
</set>
</class>
</hibernate-mapping>
然后用junit测试
TreeNodeDao
package com.huang.four.dao;
import org.hibernate.Hibernate;
import org.hibernate.Session;
import org.hibernate.Transaction;
import com.huang.four.entity.TreeNode;
import com.huang.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
package com.huang.four.dao;
import org.junit.Test;
import com.huang.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());
}
}
运行结果：
Hibernate:
select
treenode0_.tree_node_id as tree_nod1_6_0_,
treenode0_.tree_node_name as tree_nod2_6_0_,
treenode0_.tree_node_type as tree_nod3_6_0_,
treenode0_.position as position4_6_0_,
treenode0_.url as url5_6_0_,
treenode0_.parent_node_id as parent_n6_6_0_
from
t_hibernate_sys_tree_node treenode0_
where
treenode0_.tree_node_id=?
Hibernate:
select
children0_.parent_node_id as parent_n6_6_0_,
children0_.tree_node_id as tree_nod1_6_0_,
children0_.tree_node_id as tree_nod1_6_1_,
children0_.tree_node_name as tree_nod2_6_1_,
children0_.tree_node_type as tree_nod3_6_1_,
children0_.position as position4_6_1_,
children0_.url as url5_6_1_,
children0_.parent_node_id as parent_n6_6_1_
from
t_hibernate_sys_tree_node children0_
where
children0_.parent_node_id=?
Hibernate:
select
treenode0_.tree_node_id as tree_nod1_6_0_,
treenode0_.tree_node_name as tree_nod2_6_0_,
treenode0_.tree_node_type as tree_nod3_6_0_,
treenode0_.position as position4_6_0_,
treenode0_.url as url5_6_0_,
treenode0_.parent_node_id as parent_n6_6_0_
from
t_hibernate_sys_tree_node treenode0_
where
treenode0_.tree_node_id=?
TreeNode [nodeId=6, nodeName=权限管理, treeNodeType=1, position=6, url=null, initChildren=0]
TreeNode [nodeId=1, nodeName=系统管理, treeNodeType=1, position=1, url=null, initChildren=0]
[TreeNode [nodeId=10, nodeName=用户分配角色, treeNodeType=2, position=10, url=null, initChildren=0], TreeNode [nodeId=11, nodeName=角色授予用户, treeNodeType=2, position=11, url=null, initChildren=0]]
下面是多对多关联
实体类
Book
package com.huang.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();
}
}
实体映射文件
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.huang.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:对应的是中间表 没有实体类，意味着靠两张主表对应的映射文件联合管理数据
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能否影响到关联表的数据
inverse:中间表的数据维护的权利交给对方
key标签
column:当前表t_hibernate_book的主键在中间表的列段bid
many-to-many:
column:代表中间表对应的除去当前表t_hibernate_book的非主键的中间表列段
class:cid对应的类
-->
<set table="t_hibernate_book_category" name="categories" cascade="save-update" inverse="true">
<!-- one -->
<key column="bid"></key>
<!-- many -->
<many-to-many column="cid" class="com.huang.four.entity.Category"></many-to-many>
</set>
</class>
</hibernate-mapping>
注意一定要在hibernate.hbm.xml中加入以下代码：
<!-- 多对多关联 -->
<mapping resource="com/huang/four/entity/Book.hbm.xml" />
测试：
BookDao
package com.huang.four.dao;
import org.hibernate.Hibernate;
import org.hibernate.Session;
import org.hibernate.Transaction;
import com.huang.four.entity.Book;
import com.huang.four.entity.Category;
import com.huang.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();
}
}
BookDaoTest
package com.huang.four.dao;
import org.junit.Test;
import com.huang.four.entity.Book;
import com.huang.four.entity.Category;
public class BookDaoTest {
private BookDao bookDao = new BookDao();
@Test
public void testGetBook() {
Book book = new Book();
book.setBookId(8);
book.setInitCategories(1);
Book b = this.bookDao.getBook(book );
System.out.println(b.getBookName());
System.out.println(b.getCategories());
}
}
结果：
Hibernate:
select
book0_.book_id as book_id1_0_0_,
book0_.book_name as book_nam2_0_0_,
book0_.price as price3_0_0_
from
t_hibernate_book book0_
where
book0_.book_id=?
Hibernate:
select
categories0_.bid as bid1_1_0_,
categories0_.cid as cid2_1_0_,
category1_.category_id as category1_2_1_,
category1_.category_name as category2_2_1_
from
t_hibernate_book_category categories0_
inner join
t_hibernate_category category1_
on categories0_.cid=category1_.category_id
where
categories0_.bid=?
圣墟
[Category [categoryId=8, categoryName=言情], Category [categoryId=9, categoryName=言情2]]
book.hbm.xml inverse=fasle
category.hbm.xml inverse=true
数据添加正常
书籍表、桥接表各新增一条数据
package com.huang.four.dao;
import org.junit.Test;
import com.huang.four.entity.Book;
import com.huang.four.entity.Category;
public class BookDaoTest {
private BookDao bookDao = new BookDao();
@Test
public void test1() {
Book book = new Book();
book.setBookName("T226");
book.setPrice(10f);
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);
}
运行结果：
Hibernate:
select
category0_.category_id as category1_2_0_,
category0_.category_name as category2_2_0_
from
t_hibernate_category category0_
where
category0_.category_id=?
Hibernate:
select
max(book_id)
from
t_hibernate_book
Hibernate:
insert
into
t_hibernate_book
(book_name, price, book_id)
values
(?, ?, ?)
Hibernate:
update
t_hibernate_category
set
category_name=?
where
category_id=?
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
package com.huang.four.dao;
import org.junit.Test;
import com.huang.four.entity.Book;
import com.huang.four.entity.Category;
public class BookDaoTest {
private BookDao bookDao = new BookDao();
@Test
public void test2() {
Book book = new Book();
book.setBookName("T226hyc");
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);
}
}
结果：
Hibernate:
select
category0_.category_id as category1_2_0_,
category0_.category_name as category2_2_0_
from
t_hibernate_category category0_
where
category0_.category_id=?
Hibernate:
select
max(book_id)
from
t_hibernate_book
Hibernate:
insert
into
t_hibernate_book
(book_name, price, book_id)
values
(?, ?, ?)
Hibernate:
update
t_hibernate_category
set
category_name=?
where
category_id=?
