這篇講解 集合映射之List映射

1.通常對(duì)于集合，在hibernate中的處理都是使用set來完成。但是hibernate也提供了對(duì)于其他幾種集合的映射。

在這里實(shí)現(xiàn)List的映射，List是有序的集合，所以需要在表中有一列數(shù)據(jù)用來表示順序。

2.集合映射一般存在于一對(duì)多中，使用案例是 category 和 book

3.類結(jié)構(gòu)

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;}@Overridepublic 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"/><!-- 一對(duì)多的關(guān)聯(lián)映射 --><list name="books"><key column="cid"></key><!-- idx有hibernate來進(jìn)行維護(hù) --><index column="idx"/><one-to-many class="Book"/></list></class> </hibernate-mapping>

5.測試

public class HibernateTest {/*** 生成數(shù)據(jù)庫表的工具方法* */@Testpublic void testCreateDB(){Configuration cfg = new Configuration().configure();SchemaExport se = new SchemaExport(cfg);//第一個(gè)參數(shù) 是否打印sql腳本//第二個(gè)參數(shù) 是否將腳本導(dǎo)出到數(shù)據(jù)庫中執(zhí)行se.create(true, true);}/*** 初始化表數(shù)據(jù)* 使用一對(duì)多的方式來保存數(shù)據(jù)，會(huì)執(zhí)行update語句來更新外鍵* 使得效率會(huì)比多對(duì)一的方式效率低*/@Testpublic void testInit(){Session session = null;Transaction tx = null;try {session = HibernateUtil.getSession();tx = session.beginTransaction();Category c1 = new Category("計(jì)算機(jī)類");Category c2 = new Category("文學(xué)");Category c3 = new Category("歷史");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("明朝那些事兒","當(dāng)年明月",70,df.parse("2008-05-23"));Book b4 = new Book("水滸傳","老撕",20,df.parse("1985-05-23"));//設(shè)置關(guān)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();}}/*** 在查詢多的一端數(shù)據(jù)時(shí)可以獲取一的一端的數(shù)據(jù)*/@Testpublic 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();} }

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轉(zhuǎn)載于:https://www.cnblogs.com/Vincent-yuan/p/11210089.html

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