hibernate之多对多关系

hibernate的多对多
hibernate可以直接映射多对多关联关系(看作两个一对多)

下面我们拿三张表来做实例

t_book_hb

t_book_category_hb(桥接表)

t_category_hb

添加实体类及映射文件

Book

public class Book implements Serializable{
       private Integer bookId;
       private String bookName;
       private Float price;

       // 一对多：一本书对应多种书本类型
       private Set<Category> categroies=new HashSet<Category>();

       public Set<Category> getCategroies() {
            return categroies;
        }
        public void setCategroies(Set<Category> categroies) {
            this.categroies = categroies;
        }
        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 Book() {
            super();
        }

        public Book(Integer bookId, String bookName, Float price) {
            super();
            this.bookId = bookId;
            this.bookName = bookName;
            this.price = price;
        }
        @Override
        public String toString() {
            return "Book [bookId=" + bookId + ", bookName=" + bookName + ", price=" + price + "]";
        }

Book.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.hmc.hibernate02.entity.Book" table="t_book_hb">
    <id name="bookId" type="java.lang.Integer" column="book_id">
    <!--native:identity(标识列)+sequence(序列)  -->
    <generator class="native"></generator>
    </id>
    <property name="bookName" type="java.lang.String" column="book_name"/>
    <property name="price" type="java.lang.Float" column="price"/>

   <!--
    select category_id,category_name,t_category_hb c,
    t_book_category_hb bc where c.category_id=bc.cid
    -->

   <!--建立关联关系  :一对多-->
   <!--
   name:实体类中定义的属性名，指向多方
   cassade:用来控制如何操作关联的持久化对象的
   save-update/delete/none/all
   inverse:主控方
     -->
   <set name="categroies" cascade="save-update" inverse="true" table="t_book_category_hb"  >
   <!-- 对应中间表的外键列，指向一方 -->
    <key column="bid"></key>
    <!--指定实体之间的关联关系：一对多  -->
    <!--多对多关联关系-->
    <many-to-many class="com.hmc.hibernate02.entity.Category" column="cid"/>
   </set>
   </class> 

</hibernate-mapping>

Category

public class Category implements Serializable {
     private Integer categoryId;
     private String categoryName;

     //一对多：一种书本类型对应多本书
     private Set<Book> books=new HashSet<Book>();

    public Set<Book> getBooks() {
        return books;
    }
    public void setBooks(Set<Book> books) {
        this.books = books;
    }
    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 Category() {
        super();
    }
    @Override
    public String toString() {
        return "Category [categoryId=" + categoryId + ", categoryName=" + categoryName + ", books=" + books + "]";
    }

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.hmc.hibernate02.entity.Category" table="t_category_hb">
    <id name="categoryId" type="java.lang.Integer" column="category_id">
    <!--native:identity(标识列)+sequence(序列)  -->
    <generator class="native"></generator>
    </id>
    <property name="categoryName" type="java.lang.String" column="category_name"/>

   <!--一方中的主键就是多方中的外键  -->
   <!--
    select book_id,book_name,price from t_book_hb b,
    t_book_category_hb bc,t_book b  where b.book_id=bc.bid
    and bc.bid=b.book_id

    -->

   <!--建立关联关系  :一对多-->
   <!--
   name:实体类中定义的属性名，指向多方
   cassade:用来控制如何操作关联的持久化对象的
   save-update/delete/none/all
   inverse:主控方
     -->
   <set name="books" cascade="save-update" inverse="false" table="t_book_category_hb" >
   <!-- 对应中间表的外键列，指向一方 -->
    <key column="cid"></key>
    <!--指定实体之间的关联关系：多对多  -->
    <!--class:指向的是多方的实体类的全路径名  -->
    <many-to-many class="com.hmc.hibernate02.entity.Book" column="bid"/>
   </set>
   </class> 

</hibernate-mapping>

hibernate.cfg.xml

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE hibernate-configuration PUBLIC
    "-//Hibernate/Hibernate Configuration DTD 3.0//EN"
    "http://www.hibernate.org/dtd/hibernate-configuration-3.0.dtd">
    <hibernate-configuration>
       <session-factory>
       <!--1.数据库相关  -->
       <!--(connection.username|connection.password|connection.url|connection.driver_class|dialect)  -->
       <!--数据库账号  -->
      <property name="connection.username">root</property>
      <!--数据库密码  -->
      <property name="connection.password">123</property>
      <!--数据库连接的url  -->
      <!--特殊字符！！！  特殊字符！！！ 特殊字符！！！-->
      <property name="connection.url">
      jdbc:mysql://localhost:3306/book?useUnicode=true&amp;characterEncoding=UTF-8
      </property>
      <!-- 数据库连接驱动  -->
      <property name="connection.driver_class">
      com.mysql.jdbc.Driver
      </property>
      <!--数据库方言  -->
      <property name="dialect">
       org.hibernate.dialect.MySQLDialect
      </property>
       <!--2.调试相关  -->
       <!--(show_sql|format_sql)  -->
       <property name="show_sql">true</property>
       <property name="format_sql">true</property>
       <!--3.实体映射相关  -->
      <mapping resource="com/hmc/hibernate02/entity/Book.hbm.xml"/>
       <mapping resource="com/hmc/hibernate02/entity/Category.hbm.xml"/> 

       </session-factory>
    </hibernate-configuration>

BookDao

public class BookDao {

    public void addBook(Book book) {
        Session session = SessionFactoryUtils.openSession();
        Transaction transaction = session.beginTransaction();
        //保存
        session.save(book);
        transaction.commit();
        SessionFactoryUtils.closeSession();
    }

    public Book get(Book book) {
        Session session = SessionFactoryUtils.openSession();
        Transaction transaction = session.beginTransaction();
        //保存
        Book b = session.get(Book.class, book.getBookId());
        if(b!=null) {
            Hibernate.initialize(b.getCategroies());
        }
        transaction.commit();
        SessionFactoryUtils.closeSession();
        return b;
    }

    //被控方
    public void delBook(Book book) {
        Session session = SessionFactoryUtils.openSession();
        Transaction transaction = session.beginTransaction();
        Book b = session.get(Book.class, book.getBookId());
        if(null!=b) {
            //解除关联关系
            Set<Category> categroies = b.getCategroies();
            for (Category category : categroies) {
                b.getCategroies().remove(category);
            }
            session.delete(b);
        }

        transaction.commit();
        SessionFactoryUtils.closeSession();

    }
    

CategoryDao

public class CategoryDao {

    public Category get(Category category) {
        Session session = SessionFactoryUtils.openSession();
        Transaction transaction = session.beginTransaction();
        //保存
        Category c = session.get(Category.class, category.getCategoryId());
        if(c!=null) {
            Hibernate.initialize(c.getBooks());
        }
        transaction.commit();
        SessionFactoryUtils.closeSession();
        return c;
    }

    //主控方
    public void delCategory(Category c) {
        Session session = SessionFactoryUtils.openSession();
        Transaction transaction = session.beginTransaction();
        Category category = session.get(Category.class, c.getCategoryId());
        if(null!=category) {
            //解除关联关系
            Set<Book> books = c.getBooks();
            for (Book book : books) {
                //错误(删除当前书本对应的书)
                //category.getBooks().remove(book);
                //ok(删除当前书本对应的类型)
                book.getCategroies().remove(category);
            }
            session.delete(category);
        }

        transaction.commit();
        SessionFactoryUtils.closeSession();

    }
    

BookDaoTest（测试类）