1.一对多的自关联
代码演示
自关联用到TreeNode
应用场景是用来左侧数据栏加载
package com.myy.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 + ", children=" + children + "]";
// }
@Override
public String toString() {
return "TreeNode [nodeId=" + nodeId + ", nodeName=" + nodeName + ", treeNodeType=" + treeNodeType
+ ", position=" + position + ", url=" + url + "]";
}
}
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.myy.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.javaxl.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.myy.four.entity.TreeNode"/>
</set>
</class>
</hibernate-mapping>
配置到核心配置文件中hibernate.cfg.xml
<mapping resource="com/myy/four/entity/TreeNode.hbm.xml"/>
TreeNodeDao
package com.myy.four.dao;
import org.hibernate.Hibernate;
import org.hibernate.Session;
import org.hibernate.Transaction;
import com.myy.four.entity.TreeNode;
import com.myy.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.myy.four.dao;
import org.junit.Test;
import com.myy.four.entity.TreeNode;
public class TreeNodeDaoTest {
private TreeNodeDao treeNodeDao = new TreeNodeDao();
// @Before
// public void setUp() throws Exception {
// }
//
// @After
// public void tearDown() throws Exception {
// }
/**
* 注意：
* 1.这个在vue的后台搭建要用
* 2.只能加载出直系亲属（父节点，跟子节点）
* 爷爷和孙子加载不出的。左侧菜单栏只支持三级
*/
@Test
public void testLoad() {
TreeNode treeNode = new TreeNode();
// 权限管理
treeNode.setNodeId(6);
treeNode.setInitChildren(1);
TreeNode t = this.treeNodeDao.load(treeNode);
System.out.println(t);//打印当前节点
System.out.println(t.getParent());//父
System.out.println(t.getChildren());//子
}
}
运行结果：
需要用到书籍表，类别表，中间表.
首先，hibernate以面向对象的思想操作数据库，把表描述成对象。
Book
package com.myy.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;
/*
* 关联关系
* 一本书属于多个类别，多个类别用集合来装
*/
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
package com.myy.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 + "]";
}
}
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.myy.four.entity.Book" table="t_hibernate_book">
<!-- <cache usage="read-only" region="com.myy.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:指的是中间表
name:指的是实体类中关联属性
cascade:级联新增以及级联修改
inverse:中间表的数据维护交给那个实体类来控制，inverse的字面意思是反方，默认inverse=true,
那么就意味着，默认由对方来控制中间表数据的维护
key标签
column:当前映射类Book对应的表t_hibernate_book的主键，在中间表的外键
many-to-many标签：
column:当前映射类关联属性对应的类的主键，在中间表的外键
class:当前映射类关联属性对应的类的全路径名
-->
<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.myy.four.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.myy.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.myy.four.entity.Book"></many-to-many>
</set>
</class>
</hibernate-mapping>
hibernate.cfg.xml配置
<!-- 多对多的讲解 -->
<mapping resource="com/myy/four/entity/Book.hbm.xml" />
<mapping resource="com/myy/four/entity/Category.hbm.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/db_xm?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/myy/one/entity/User.hbm.xml" />
<!-- 讲解主键生产策略 -->
<mapping resource="com/myy/two/entity/Student.hbm.xml" />
<mapping resource="com/myy/two/entity/Worker.hbm.xml" />
<!--一对多的讲解 -->
<mapping resource="com/myy/three/entity/Order.hbm.xml" />
<mapping resource="com/myy/three/entity/OrderItem.hbm.xml" />
<!-- 一对多的自关联 -->
<mapping resource="com/myy/four/entity/TreeNode.hbm.xml" />
<!-- 多对多的讲解 -->
<mapping resource="com/myy/four/entity/Book.hbm.xml" />
<mapping resource="com/myy/four/entity/Category.hbm.xml" />
</session-factory>
</hibernate-configuration>
测试代码
场景一
BookDao
package com.myy.four.dao;
import org.hibernate.Hibernate;
import org.hibernate.Session;
import org.hibernate.Transaction;
import com.myy.four.entity.Book;
import com.myy.four.entity.Category;
import com.myy.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.myy.four.dao;
import org.junit.Test;
import com.myy.four.entity.Book;
import com.myy.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());
}
/**
* 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("小王子myy2");
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);
}
}
运行查询testGetBook方法结果：
运行新增test1方法：
结果是两张表都加数据
场景二
注意
当category.hbm.xml的inverse="false"时
book.hbm.xml的inverse="true"时
再运行测试BookDaoTest的test1方法:
运行结果发现：只有书籍表加了数据，中间表没有加
inverse代表中间表的数据是否维护，false代表自己维护。inverse默认为对方维护，改成false意味着只有Category它能维护中间表的数据、book.getCategories().add©;----book加进去，book不能维护，中间表的数据不添加。哪怕是一正一反，如果说你维护的对象不对，中间的数据依然不会添加
场景三
当inverse都为true时：
意味着都不维护中间表的数据
运行test2方法结果为：
只有数据表加了数据，中间表没有加
hibernate 中多对多的查询原理：
1. 建模得到了sessionfactory工厂
2. sessionfactory中包含两个多对多的关系映射文件，那么就可以通过流加载那个两个映射文件这里以com/myy/four/entity/Category.hbm.xml，加载完后可以对其建模
3. 可以拿到com/myy/four/entity/Category.hbm以及表t_hibernate_category。通过t_hibernate_category以及下列的column列段可以多态生成sql语句
select category_id,category_name from t_hibernate_category where category_id=?(假设 5)
查询结果： 5 a1
反射实例化：
Category c = Class.forName("com/myy/four/entity/category.hbm.xml")
Field categoryNameField = c.getClass().getDecafiedld("categoryName")
categoryNameField.setAccessable(true);打开权限
categoryNameField.set(c,"a1");
同理必然有id：
categoryIdField.set(c,"a1");
那意味着当前c实例中已经所有属性值已经赋值完毕
4. 同样对此文件com/myy/four/entity/Category.hbm.xml建模，可以得到中间表t_hibernate_book_category以及关联属性全路径名com.myy.four.entity.Book
自然形成一个sql语句反射：
select cid,bid from t_hibernate_book_category where cid=?(假设 5)
查询结果:
5 17 5
6 20 5
7 21 5
8 22 5
.........
意味着反射：
String sql =selcet * from t_hibernate_book where book_id in (17,20,...)查出一个集合
List<Book> books = BaseDao.executeQuery(sql,Book.class,null)
Book.class通过建模得到，sql由自动生成得到
以前BaseDao.executeQuery(sql,Class clz,pagebean),传Class clz是为了不断创建一个新的对象
5. c.setBooks(books)
需要用到三次反射两次建模，所以hibernate做一个查询要用这么多，则性能很低
