Hibernate.orgCommunity Documentation

Chapter 25. Example: Weblog Application

25.1. Persistent Classes
25.2. Hibernate Mappings
25.3. Hibernate Code

25.1. Persistent Classes

The persistent classes here represent a weblog and an item posted in a weblog. They are to be modelled as a standard parent/child relationship, but we will use an ordered bag, instead of a set: 

package eg;


import java.util.List;


public class Blog {

    private Long _id;

    private String _name;

    private List _items;


    public Long getId() {

        return _id;

    }

    public List getItems() {

        return _items;

    }

    public String getName() {

        return _name;

    }

    public void setId(Long long1) {

        _id = long1;

    }

    public void setItems(List list) {

        _items = list;

    }

    public void setName(String string) {

        _name = string;

    }

}
package eg;


import java.text.DateFormat;

import java.util.Calendar;


public class BlogItem {

    private Long _id;

    private Calendar _datetime;

    private String _text;

    private String _title;

    private Blog _blog;


    public Blog getBlog() {

        return _blog;

    }

    public Calendar getDatetime() {

        return _datetime;

    }

    public Long getId() {

        return _id;

    }

    public String getText() {

        return _text;

    }

    public String getTitle() {

        return _title;

    }

    public void setBlog(Blog blog) {

        _blog = blog;

    }

    public void setDatetime(Calendar calendar) {

        _datetime = calendar;

    }

    public void setId(Long long1) {

        _id = long1;

    }

    public void setText(String string) {

        _text = string;

    }

    public void setTitle(String string) {

        _title = string;

    }

}

25.2. Hibernate Mappings

The XML mappings are now straightforward. For example: 


<?xml version="1.0"?>

<!DOCTYPE hibernate-mapping PUBLIC

    "-//Hibernate/Hibernate Mapping DTD 3.0//EN"

    "http://www.hibernate.org/dtd/hibernate-mapping-3.0.dtd">



<hibernate-mapping package="eg">



    <class

        name="Blog"

        table="BLOGS">



        <id

            name="id"

            column="BLOG_ID">



            <generator class="native"/>



        </id>



        <property

            name="name"

            column="NAME"

            not-null="true"

            unique="true"/>



        <bag

            name="items"

            inverse="true"

            order-by="DATE_TIME"

            cascade="all">



            <key column="BLOG_ID"/>

            <one-to-many class="BlogItem"/>



        </bag>



    </class>



</hibernate-mapping>



<?xml version="1.0"?>

<!DOCTYPE hibernate-mapping PUBLIC

    "-//Hibernate/Hibernate Mapping DTD 3.0//EN"

    "http://www.hibernate.org/dtd/hibernate-mapping-3.0.dtd">



<hibernate-mapping package="eg">



    <class

        name="BlogItem"

        table="BLOG_ITEMS"

        dynamic-update="true">



        <id

            name="id"

            column="BLOG_ITEM_ID">



            <generator class="native"/>



        </id>



        <property

            name="title"

            column="TITLE"

            not-null="true"/>



        <property

            name="text"

            column="TEXT"

            not-null="true"/>



        <property

            name="datetime"

            column="DATE_TIME"

            not-null="true"/>



        <many-to-one

            name="blog"

            column="BLOG_ID"

            not-null="true"/>



    </class>



</hibernate-mapping>

25.3. Hibernate Code

The following class demonstrates some of the kinds of things we can do with these classes using Hibernate: 

package eg;


import java.util.ArrayList;

import java.util.Calendar;

import java.util.Iterator;

import java.util.List;


import org.hibernate.HibernateException;

import org.hibernate.Query;

import org.hibernate.Session;

import org.hibernate.SessionFactory;

import org.hibernate.Transaction;

import org.hibernate.cfg.Configuration;

import org.hibernate.tool.hbm2ddl.SchemaExport;


public class BlogMain {

    

    private SessionFactory _sessions;

    

    public void configure() throws HibernateException {

        _sessions = new Configuration()

            .addClass(Blog.class)

            .addClass(BlogItem.class)

            .buildSessionFactory();

    }

    

    public void exportTables() throws HibernateException {

        Configuration cfg = new Configuration()

            .addClass(Blog.class)

            .addClass(BlogItem.class);

        new SchemaExport(cfg).create(true, true);

    }

    

    public Blog createBlog(String name) throws HibernateException {

        

        Blog blog = new Blog();

        blog.setName(name);

        blog.setItems( new ArrayList() );

        

        Session session = _sessions.openSession();

        Transaction tx = null;

        try {

            tx = session.beginTransaction();

            session.persist(blog);

            tx.commit();

        }

        catch (HibernateException he) {

            if (tx!=null) tx.rollback();

            throw he;

        }

        finally {

            session.close();

        }

        return blog;

    }

    

    public BlogItem createBlogItem(Blog blog, String title, String text)

                        throws HibernateException {

        

        BlogItem item = new BlogItem();

        item.setTitle(title);

        item.setText(text);

        item.setBlog(blog);

        item.setDatetime( Calendar.getInstance() );

        blog.getItems().add(item);

        

        Session session = _sessions.openSession();

        Transaction tx = null;

        try {

            tx = session.beginTransaction();

            session.update(blog);

            tx.commit();

        }

        catch (HibernateException he) {

            if (tx!=null) tx.rollback();

            throw he;

        }

        finally {

            session.close();

        }

        return item;

    }

    

    public BlogItem createBlogItem(Long blogid, String title, String text)

                        throws HibernateException {

        

        BlogItem item = new BlogItem();

        item.setTitle(title);

        item.setText(text);

        item.setDatetime( Calendar.getInstance() );

        

        Session session = _sessions.openSession();

        Transaction tx = null;

        try {

            tx = session.beginTransaction();

            Blog blog = (Blog) session.load(Blog.class, blogid);

            item.setBlog(blog);

            blog.getItems().add(item);

            tx.commit();

        }

        catch (HibernateException he) {

            if (tx!=null) tx.rollback();

            throw he;

        }

        finally {

            session.close();

        }

        return item;

    }

    

    public void updateBlogItem(BlogItem item, String text)

                    throws HibernateException {

        

        item.setText(text);

        

        Session session = _sessions.openSession();

        Transaction tx = null;

        try {

            tx = session.beginTransaction();

            session.update(item);

            tx.commit();

        }

        catch (HibernateException he) {

            if (tx!=null) tx.rollback();

            throw he;

        }

        finally {

            session.close();

        }

    }

    

    public void updateBlogItem(Long itemid, String text)

                    throws HibernateException {

    

        Session session = _sessions.openSession();

        Transaction tx = null;

        try {

            tx = session.beginTransaction();

            BlogItem item = (BlogItem) session.load(BlogItem.class, itemid);

            item.setText(text);

            tx.commit();

        }

        catch (HibernateException he) {

            if (tx!=null) tx.rollback();

            throw he;

        }

        finally {

            session.close();

        }

    }

    

    public List listAllBlogNamesAndItemCounts(int max)

                    throws HibernateException {

        

        Session session = _sessions.openSession();

        Transaction tx = null;

        List result = null;

        try {

            tx = session.beginTransaction();

            Query q = session.createQuery(

                "select blog.id, blog.name, count(blogItem) " +

                "from Blog as blog " +

                "left outer join blog.items as blogItem " +

                "group by blog.name, blog.id " +

                "order by max(blogItem.datetime)"

            );

            q.setMaxResults(max);

            result = q.list();

            tx.commit();

        }

        catch (HibernateException he) {

            if (tx!=null) tx.rollback();

            throw he;

        }

        finally {

            session.close();

        }

        return result;

    }

    

    public Blog getBlogAndAllItems(Long blogid)

                    throws HibernateException {

        

        Session session = _sessions.openSession();

        Transaction tx = null;

        Blog blog = null;

        try {

            tx = session.beginTransaction();

            Query q = session.createQuery(

                "from Blog as blog " +

                "left outer join fetch blog.items " +

                "where blog.id = :blogid"

            );

            q.setParameter("blogid", blogid);

            blog  = (Blog) q.uniqueResult();

            tx.commit();

        }

        catch (HibernateException he) {

            if (tx!=null) tx.rollback();

            throw he;

        }

        finally {

            session.close();

        }

        return blog;

    }

    

    public List listBlogsAndRecentItems() throws HibernateException {

        

        Session session = _sessions.openSession();

        Transaction tx = null;

        List result = null;

        try {

            tx = session.beginTransaction();

            Query q = session.createQuery(

                "from Blog as blog " +

                "inner join blog.items as blogItem " +

                "where blogItem.datetime > :minDate"

            );


            Calendar cal = Calendar.getInstance();

            cal.roll(Calendar.MONTH, false);

            q.setCalendar("minDate", cal);

            

            result = q.list();

            tx.commit();

        }

        catch (HibernateException he) {

            if (tx!=null) tx.rollback();

            throw he;

        }

        finally {

            session.close();

        }

        return result;

    }

}

Copyright © 2004 Red Hat, Inc.