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
注：数据库多表联接查询
永远就是二个表的联接查询
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
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)
案例：
自关联查询：
新建一个TreeNode实体类：
package com.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 + ", children=" + children + "]";
// } @Override
public String toString() {
return "TreeNode [nodeId=" + nodeId + ", nodeName=" + nodeName + ", treeNodeType=" + treeNodeType
+ ", position=" + position + ", url=" + url + "]";
} }
在同包下导入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.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.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.entity.TreeNode"/>
</set>
</class>
</hibernate-mapping>
dao:
TreeNodeDao.java:
package com.dao; import org.hibernate.Hibernate;
import org.hibernate.Session;
import org.hibernate.Transaction; import com.entity.TreeNode;
import com.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;
}
}
进行测试：
package com.dao;
import org.junit.Test;
import com.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());
}
}
在hibernate.cfg.xlm中添加映射文件（一对多自关联、多对多关联）：
<?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/mysql?useUnicode=true&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/entity/user.hbm.xml" /> <!-- 主键生成策略 -->
<mapping resource="com/entity/Worker.hbm.xml" />
<mapping resource="com/entity/Student.hbm.xml" />
<!-- 关联关系(一对多) -->
<mapping resource="com/entity/Order.hbm.xml" />
<mapping resource="com/entity/OrderItem.hbm.xml" />
<!-- 一对多自关联 -->
<mapping resource="com/entity/TreeNode.hbm.xml" />
<!-- 多对多关联 -->
<mapping resource="com/entity/Book.hbm.xml" />
<mapping resource="com/entity/category.hbm.xml" />
</session-factory>
</hibernate-configuration>
测试结果：
多对多级联查询：
Book.java:
package com.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();
} }
category.java:
package com.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 + "]";
} }
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 name="com.entity.Book" table="t_hibernate_book">
<cache usage="read-only" region="com.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，靠两张表 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（当前实体类对应的表 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:
column：当前表的主键在中间表的列段
-->
<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.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.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.entity.Book"></many-to-many>
</set>
</class>
</hibernate-mapping>
BookDao.java:
package com.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.entity.Book;
import com.entity.Category;
import com.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.java:
package com.dao; import org.junit.Test; import com.entity.Book;
import com.entity.Category; public class BookDaoTest {
private BookDao bookDao = new BookDao(); @Test
public void testGetBook() {
Book book = new Book();
book.setBookId(5);
book.setInitCategories(1);
Book b = this.bookDao.getBook(book );
System.out.println(b.getBookName());
System.out.println(b.getCategories());
} /**
* 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
*/
@Test
public void test1() {
Book book = new Book();
book.setBookName("0030");
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);
} /**
* 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);
} }
testGetBook:
test1:
test2:
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