这篇讲解 双向的多对一关联映射
1.表结构和多对一时，一致
2.类结构
Book.java
public class Book implements Serializable{
private int id;
private String name;
private String author;
private double price;
private Date pubDate;
private Category category;
public Book() {
}
public Book(String name, String author, double price, Date pubDate) {
super();
this.name = name;
this.author = author;
this.price = price;
this.pubDate = pubDate;
}
public int getId() {
return id;
}
public void setId(int id) {
this.id = id;
}
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
public String getAuthor() {
return author;
}
public void setAuthor(String author) {
this.author = author;
}
public double getPrice() {
return price;
}
public void setPrice(double price) {
this.price = price;
}
public Date getPubDate() {
return pubDate;
}
public void setPubDate(Date pubDate) {
this.pubDate = pubDate;
}
public Category getCategory() {
return category;
}
public void setCategory(Category category) {
this.category = category;
}
}Category.java
public class Category implements Serializable{
private int id;
private String name;
private Set<Book> books = new HashSet<Book>();
public Category() {
}
public Category(String name) {
super();
this.name = name;
}
public int getId() {
return id;
}
public void setId(int id) {
this.id = id;
}
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
public Set<Book> getBooks() {
return books;
}
public void setBooks(Set<Book> books) {
this.books = books;
}
}3.映射文件
Book.hbm.xml
<hibernate-mapping package="cn.sxt.pojo">
<class name="Book" table="t_book">
<id name="id">
<generator class="native"></generator>
</id>
<property name="name"/>
<property name="author"/>
<property name="price"/>
<property name="pubDate"/>
<!-- 多对一的关联关系设置 column指定外键的名称 -->
<many-to-one name="category" column="cid"/>
</class>
</hibernate-mapping>
Category.hbm.xml
<hibernate-mapping package="cn.sxt.pojo">
<class name="Category" table="t_category">
<id name="id">
<generator class="native"></generator>
</id>
<property name="name"/>
<!-- 双向一对多的设置 -->
<set name="books" inverse="true">
<!-- 设置外键 -->
<key column="cid"></key>
<!-- 设置多的一端的类型 -->
<one-to-many class="Book"/>
</set>
</class>
</hibernate-mapping>
4.测试
public class HibernateTest {
/**
* 生成数据库表的工具方法
* */
@Test
public void testCreateDB(){
Configuration cfg = new Configuration().configure();
SchemaExport se = new SchemaExport(cfg);
//第一个参数 是否打印sql脚本
//第二个参数 是否将脚本导出到数据库中执行
se.create(true, true);
}
/**
* 初始化表数据
*/
@Test
public void testInit(){
Session session = null;
Transaction tx = null;
try {
session = HibernateUtil.getSession();
tx = session.beginTransaction();
Category c1 = new Category("计算机类");
Category c2 = new Category("文学");
Category c3 = new Category("历史");
SimpleDateFormat df = new SimpleDateFormat("yyyy-MM-dd");
Book b1 = new Book("java","sun",30,df.parse("1995-05-23"));
b1.setCategory(c1);
Book b2 = new Book("struts","apache",40,df.parse("2006-09-12"));
b2.setCategory(c1);
Book b3 = new Book("明朝那些事儿","当年明月",70,df.parse("2008-05-23"));
b3.setCategory(c3);
Book b4 = new Book("水浒传","老撕",20,df.parse("1985-05-23"));
b4.setCategory(c2);
session.save(c1);
session.save(c2);
session.save(c3);
session.save(b1);
session.save(b2);
session.save(b3);
session.save(b4);
tx.commit();
} catch (Exception e) {
if(tx!=null)
tx.rollback();
}finally {
HibernateUtil.close();
}
}
/**
* 在查询多的一端数据时可以获取一的一端的数据
*/
@Test
public void testGetData(){
Session session = HibernateUtil.getSession();
Book book = (Book)session.get(Book.class, 3);
System.out.println(book.getId()+"--"+book.getName()+"---"+book.getAuthor()+
"---"+book.getPrice()+"---"+book.getPubDate()+"---"+book.getCategory().getName());
System.out.println("=============================");
Category c1 = (Category)session.get(Category.class, 1);
System.out.println(c1.getId()+"-----"+c1.getName());
for(Book b:c1.getBooks()){
System.out.println(b);
}
HibernateUtil.close();
}
}