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package org.appfuse.dao.jpa;

import org.apache.commons.logging.Log;
import org.apache.commons.logging.LogFactory;
import org.appfuse.dao.GenericDao;

import javax.persistence.EntityManager;
import javax.persistence.EntityNotFoundException;
import javax.persistence.PersistenceContext;
import java.io.Serializable;
import java.util.ArrayList;
import java.util.Collection;
import java.util.LinkedHashSet;
import java.util.List;

/**
 * This class serves as the Base class for all other DAOs - namely to hold
 * common CRUD methods that they might all use. You should only need to extend
 * this class when your require custom CRUD logic.
 *
 * To register this class in your Spring context file, use the following XML.
 * 
 *      <bean id="fooDao" class="org.appfuse.dao.hibernate.GenericDaoJpaHibernate">
 *          <constructor-arg value="org.appfuse.model.Foo"/>
 *          <property name="sessionFactory" ref="sessionFactory"/>
 *      </bean>
 * 
 *
 * @author Bryan Noll
 * @param  a type variable
 * @param  the primary key for that type
 */
public class GenericDaoJpa implements GenericDao {
    /**
     * Log variable for all child classes. Uses LogFactory.getLog(getClass()) from Commons Logging
     */
    protected final Log log = LogFactory.getLog(getClass());

    public static final String PERSISTENCE_UNIT_NAME = "ApplicationEntityManager";
    
    /**
     * Entity manager, injected by Spring using @PersistenceContext annotation on setEntityManager()
     */
    @PersistenceContext(unitName=PERSISTENCE_UNIT_NAME)
    private EntityManager entityManager;
    private Class persistentClass;

    /**
     * Constructor that takes in a class to see which type of entity to persist.
     * Use this constructor when subclassing or using dependency injection.
     * @param persistentClass the class type you'd like to persist
     */
    public GenericDaoJpa(final Class persistentClass) {
        this.persistentClass = persistentClass;
    }

    /**
     * Constructor that takes in a class to see which type of entity to persist.
     * Use this constructor when subclassing or using dependency injection.
     * @param persistentClass the class type you'd like to persist
     * @param entityManager the configured EntityManager for JPA implementation.
     */
    public GenericDaoJpa(final Class persistentClass, EntityManager entityManager) {
        this.persistentClass = persistentClass;
        this.entityManager = entityManager;
    }

    public EntityManager getEntityManager() {
        return this.entityManager;
    }
    
    /**
     * {@inheritDoc}
     */
    @SuppressWarnings("unchecked")
    public List getAll() {
        return this.entityManager.createQuery(
                "select obj from " + this.persistentClass.getName() + " obj")
                .getResultList();
    }

    /**
     * {@inheritDoc}
     */
    @SuppressWarnings("unchecked")
    public List getAllDistinct() {
        Collection result = new LinkedHashSet(getAll());
        return new ArrayList(result);
    }

    /**
     * {@inheritDoc}
     */
    public T get(PK id) {
        T entity = this.entityManager.find(this.persistentClass, id);

        if (entity == null) {
            String msg = "Uh oh, '" + this.persistentClass + "' object with id '" + id + "' not found...";
            log.warn(msg);
            throw new EntityNotFoundException(msg);
        }

        return entity;
    }

    /**
     * {@inheritDoc}
     */
    public boolean exists(PK id) {
        T entity = this.entityManager.find(this.persistentClass, id);
        return entity != null;
    }

    /**
     * {@inheritDoc}
     */
    public T save(T object) {
        return this.entityManager.merge(object);
    }

    /**
     * {@inheritDoc}
     */
    public void remove(PK id) {
        this.entityManager.remove(this.get(id));
    }
}