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
     
       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
      
        getBooks() {        return books;    }    public void setBooks(List
       
         books) {        this.books = books;    }}
       
      
     

4.映射文件

Book.hbm.xml

Category.hbm.xml

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();    }}