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Hibernate Generic DAO.

Posted by JOKe on 8/19/2009 11:53:00 AM

When you use Hibernate and DAO pattern it is a good idea to use a Generic Base Dao. The fallowing code snippet contains GenericDAO that is a base class for all my DAO classes. This GenericDAO uses HibernateDaoSupport from Spring for its implementation if you want you can use JpaDaoSupport or JdbcDaoSupport in your projects.

My Generic DAO interface looks like this :

package org.joke.myproject.dao.base;

import java.io.Serializable;

import java.util.List;

/**

* @author Naiden Gochev

* @param <E>

* @param <PK>

*/

public interface GenericDao<E,PK  extends Serializable> {

    PK save(E newInstance);

    void update(E transientObject);

    void saveOrUpdate(E transientObject);

    void delete(E persistentObject);

    E findById(PK id);

    List<E> findAll();

    List<E> findAllByProperty(String propertyName,Object value);

}

All method names are very common so I don't think they need some explanation.

The implementation of this GenericDAO :

package org.joke.myproject.dao.base;

 

import java.io.Serializable;

import java.util.List;

import org.hibernate.criterion.DetachedCriteria;

import org.hibernate.criterion.Restrictions;

import org.springframework.orm.hibernate3.support.HibernateDaoSupport;

/**

* @author JOKe

* @param <E>

* @param <PK>

*/

public abstract class GenericDaoImpl<E, PK extends Serializable> extends

            HibernateDaoSupport implements GenericDao<E, PK> {

      @SuppressWarnings("unchecked")

      public PK save(E newInstance) {

            return (PK) getHibernateTemplate().save(newInstance);

      }

      @SuppressWarnings("unchecked")

      public E findById(PK id) {

            return (E) getHibernateTemplate().get(getEntityClass(), id);

      }

      @SuppressWarnings("unchecked")

      public List<E> findAll() {

            return getHibernateTemplate().findByCriteria(createDetachedCriteria());

      }

      @SuppressWarnings("unchecked")

      public List<E> findAllByProperty(String propertyName, Object value) {

            DetachedCriteria criteria = createDetachedCriteria();

            criteria.add(Restrictions.eq(propertyName, value));

            return getHibernateTemplate().findByCriteria(criteria);

      }

      public List<E> findByExample(E object) {

            List<E> resultList = getHibernateTemplate().findByExample(object, 0, 1);

            return resultList;

      }

      public List<E> findByExample(E object, int firstResult, int maxResults) {

            List<E> resultList = getHibernateTemplate().findByExample(object,

                        firstResult, maxResults);

            return resultList;

      }

      public void update(E transientObject) {

            getHibernateTemplate().update(transientObject);

      }

      public void saveOrUpdate(E transientObject) {

            getHibernateTemplate().saveOrUpdate(transientObject);

      }

      public void delete(E persistentObject) {

            getHibernateTemplate().delete(persistentObject);

      }

      protected abstract Class<E> getEntityClass();

      protected DetachedCriteria createDetachedCriteria() {

            return DetachedCriteria.forClass(getEntityClass());

      }

}

The GenericDaoImpl is abstract because the actual DAOs will extend it and will override only one method :  protected abstract Class<E> getEntityClass(); This method is used for creating of the DetachedCriteria object in the createDetachedCriteria() method.

Every DAO class that implements GenericDaoImpl will look like this :

package org.joke.myproject.dao;

 

import java.util.List;

import org.hibernate.criterion.DetachedCriteria;

import org.hibernate.criterion.Restrictions;

import org.joke.myproject.dao.base.GenericDaoImpl;

import org.joke.myproject.entity.Message;

 

public class MessagesDAO extends GenericDaoImpl<Message, Integer> {

      @Override

      protected Class<Message> getEntityClass() {

            return Message.class;

      }

      public List<Message> findNotDeletedTextMessages() {

            DetachedCriteria criteria = createDetachedCriteria();

            criteria.add(Restrictions.eq("deleted", false));

            criteria.add(Restrictions.or(Restrictions.eq("custom", false), Restrictions.isNull("custom")));

            List<Message> textMessages = getHibernateTemplate().findByCriteria(criteria);

            return textMessages;

      }

}

The method here called findNotDeletedTextMessages() is optional it is just another DAO method added in the implementation. If you use Spring you can just add the annotation @Component as class annotation and you have DAO ready for use.

That's all have fun.

Edit : Check out my next article called  JSF, Spring, Hibernate – lets make development easy. It will use this GenericDAO to make architecture of an application.


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10 Comments


Nice post.

Though as I mentioned here I would prefer to throw HibernateTemplate away and use plain hibernate 3 style instead.


:) maybe it is better but the most common way is to use template(s).


Hey, this is pretty similar to the way my apps are set up... one slight difference is that rather than having an abstract method to get the persistent class, I use some good old reflection.

In the base dao constructor, I have the following:

ParameterizedType pType = (ParameterizedType) getClass().getGenericSuperclass();
this.persistentClass = (Class<T>) pType.getActualTypeArguments()[0];


So if the implementation extends GenericDaoImpl<Message, Integer>, this.persistentClass will be a Message.class.

I think I originally got this from Christian Bauer's blog.

So long as you're on Sun's JVM 1.5+ the reflection's lightning fast, and as it only runs once per dao instance (probably during the apps bootstrap phase) there's really no reason not to do this (in my opinion).


Hm yes you are right there is only one instance of this DAO so the reflection will not slow the application. Thanks man :) I will "update" my projects genericDao :D


Very good. I did one minor change, because we deal with multiple Hibernate session factories. In such a scenario they need to pass in into the constructor:

@SuppressWarnings("unchecked")
protected GenericDaoImpl(SessionFactory sf) {
setSessionFactory(sf);
}

And then each concrete implementation passes in the SessionFactory that it is actually bound to:

@Autowired
public ConcreteDao(@Qualifier(ApsConstants.LOCAL_HSF) SessionFactory sf) {
super(sf);
}


Nothing against your generic dao implementation, but I've been using this project recently and have been pleased.
http://code.google.com/p/hibernate-generic-dao/


Is it in appfuse a long time ago?


Very useful information. Keep on posting. www.javatutoronline.com


the classes User and AuctionDataProvider must be Serializable, then works fine.

tested on JBoss 4.2.1.


It is very very informative. I liked the way you have explained.Java Online Training

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