本文详细介绍了Hibernate框架下如何实现自关联及多对多关联关系的配置与操作，包括一对多自关联的TreeNode实体类及其映射文件、DAO类实现，以及多对多关联的Book和Category实体类配置、中间表处理方式等。
hibernate关联关系（多对多）
一对多的自关联
有时我们会碰到一张表中存在着上下级关系，这时就需要用到自关联。
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.shl.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.shl.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.shl.four.entity.TreeNode"/>
</set>
</class>
</hibernate-mapping>
TreeNode
package com.shl.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;
//父节点
private TreeNode parent;
//子节点
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;
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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 + "]";
}
}
TreeNodeDao
package com.shl.four.dao;
import org.hibernate.Hibernate;
import org.hibernate.Session;
import org.hibernate.Transaction;
import com.shl.four.entity.TreeNode;
import com.shl.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
用Junit进行测试
package com.shl.four.dao;
import org.junit.Test;
import com.shl.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());
}
}
结果：可以把节点的父节点和字节点一起查出来
多对多关联关系
这里以书籍表，书籍类别表和一个中间关联表来进行讲解
我们不用在eclipse中建立中间表的实体类，只需在xml配置就行
book.hbm.xml
这里有个inverse，如果xml里inverse=false，意思就是中间表的数据有该类进行操控，等于true就不处理
<?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.shl.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>
<!--
table:代表中间表
name: 书籍类的关联属性
inverse:中间表交给对方维护
key:当前类对应的表列段在中间表(t_hibernate_book_category)的外键bid
many-to-many:
column:对应的是上面key查出来中间表(t_hibernate_book_category)的另一个主键cid，当做关联表的主键(category_id)进行查询
class:上述查出来的主键对应的实体类
流程：以查询book_id=1西游记为例
1.通过建模反射自动生成sql，可以拿到book_id=1这条记录的基本信息{book_id=1,book_name=西游记,price=50}
2.book_id=1->bid=1查询中间表t_hibernate_book_category，拿到了cid=1，2
3.cid=1，2->t_hibernate_category的category_id=1,2
4.拿到了当前book实例对应的category集合
5.最终{book_id=1,book_name=西游记,price=50}->{book_id=1,book_name=西游记,price=50,categories=[{...},{...}]}
-->
<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.shl.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.shl.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.shl.four.entity.Book"></many-to-many>
</set>
</class>
</hibernate-mapping>
Book
package com.shl.four.entity;
import java.io.Serializable;
import java.util.HashSet;
import java.util.Set;
public class Book implements Serializable{
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
package com.shl.four.entity;
import java.io.Serializable;
import java.util.HashSet;
import java.util.Set;
public class Category implements Serializable{
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 + "]";
}
}
BookDao
package com.shl.four.dao;
import org.hibernate.Hibernate;
import org.hibernate.Session;
import org.hibernate.Transaction;
import com.shl.four.entity.Book;
import com.shl.four.entity.Category;
import com.shl.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.shl.four.dao;
import org.junit.Test;
import com.shl.four.entity.Book;
import com.shl.four.entity.Category;
public class BookDaoTest {
private BookDao bookDao = new BookDao();
@Test
public void testGetBook() {
Book book = new Book();
book.setBookId(1);
book.setInitCategories(1);
Book b = this.bookDao.getBook(book );
System.out.println(b.getBookName());
System.out.println(b.getCategories());
}
/**
* book.hbm.xml inverse=fasle 处理中间表的数据
* category.hbm.xml inverse=true 不处理
* 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("zdb");
book.setPrice(10f);
Category category = new Category();
category.setCategoryId(3);
// 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);
}
}
当我们增加一本书时，会在中间表中加入一条对应的数据
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