Using Hibernate Transformers

There are times we have a class, we would like to fill with data according the data returned from a query. The class is a simple POJO and not an Hibernate entity, so Hibernate won’t recognize this class.
This can be done in Hibernate by using Transformers. Let’s have a look on a simple example, showing how Transformers can be used. First, let’s have a look at a simple POJO class named: “UserActivityStat”.
This class contains some statistical information. We would like to fill the statistical information of an instance, directly from running an Hibernate HQL.

public class UserActivityStat

{

private int totalPhotos;

private int totalViews;


public UserActivityStat() {

}


public int getTotalPhotos() {

return totalPhotos;

}


public void setTotalPhotos(int totalPhotos) {

this.totalPhotos = totalPhotos;

}


public int getTotalViews() {

return totalViews;

}


public void setTotalViews(int totalViews) {

this.totalViews = totalViews;

}

}

Now, let’s have a look at a simple method, that uses hibernate HQL and the Transformers class to fill “UserActivityStat” instance with data:

public UserActivityStat getUserActivityStat(User user)

{

return (UserActivityStat)hibernateSession.createQuery("select count(*) as totalPhotos, sum(p.views) as totalViews " +

"from Photo p where p.user = :user " +

"p.dateCreated  <= :now").

setParameter("user", user).

setTimestamp("now", new Date()).

setResultTransformer(Transformers.aliasToBean(UserActivityStat.class)).uniqueResult();

}

Note, that each of the 2 columns has an alias. This alias must be the name of the property on the “UserActivityStat” class. Also note for the use of the “setResultTransformer” along the “Transformers” class.