这篇讲解 集合映射之List映射
1.通常对于集合,在hibernate中的处理都是使用set来完成。但是hibernate也提供了对于其他几种集合的映射。
在这里实现List的映射,List是有序的集合,所以需要在表中有一列数据用来表示顺序。
2.集合映射一般存在于一对多中,使用案例是 category 和 book
3.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;
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;
}
@Override
public String toString() {
return "Book [id=" + id + ", name=" + name + ", author=" + author + ", price=" + price + ", pubDate=" + pubDate
+ "]";
}
}
Category.java
public class Category implements Serializable{
private int id;
private String name;
private List<Book> books = new ArrayList<>();
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 List<Book> getBooks() {
return books;
}
public void setBooks(List<Book> books) {
this.books = books;
}
}
4.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"/>
</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"/>
<!-- 一对多的关联映射 -->
<list name="books">
<key column="cid"></key>
<!-- idx有hibernate来进行维护 -->
<index column="idx"/>
<one-to-many class="Book"/>
</list>
</class>
</hibernate-mapping>
5.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
* 使用一对多的方式来保存数据,会执行update语句来更新外键
* 使得效率会比多对一的方式效率低
*/
@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"));
Book b2 = new Book("struts","apache",40,df.parse("2006-09-12"));
Book b3 = new Book("明朝那些事儿","当年明月",70,df.parse("2008-05-23"));
Book b4 = new Book("水浒传","老撕",20,df.parse("1985-05-23"));
//设置关系
c1.getBooks().add(b1);
c1.getBooks().add(b2);
c2.getBooks().add(b4);
c3.getBooks().add(b3);
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();
Category c1 = (Category)session.get(Category.class, 1);
System.out.println(c1.getId()+"----"+c1.getName());
System.out.println("-----------------");
for(Book book:c1.getBooks()){
System.out.println(book);
}
HibernateUtil.close();
}
}