Using detached Criteria [SPR-1254]

[spring-projects-issues]

Frank Verbruggen opened SPR-1254 and commented

My software developers use the HibernateTemplate and HibernateDAOSupport classes to combine Spring 1.2 final and Hibernate 3.
I wanted to hide all session management and transaction management from them, so we used a configured transaction interceptor, also by Spring.
All was well until we decided upon using the Criteria interface by Hibernate.
Since I hid the session management from my team they could not use Criteria objects, and there was no support in HibernateTemplate, nor in HibernateDAOSupport.
The next step was for me to take a looksy in the source code.
After some investigation, I found that support wasn't available, so I decided to use my own classes.
The following 2 methods were added to HibernateTemplate:

<code>
public CriteriaImpl getDetachedCriteria(Class persistentClass){
return new CriteriaImpl(persistentClass.getName(), null);
}

public List find(final CriteriaImpl detachedCriteria){
	return (List) execute(new HibernateCallback() {
		public Object doInHibernate(Session session) throws HibernateException {
			detachedCriteria.setSession((SessionImpl) session);
			return detachedCriteria.list();
		}
	}, true);		
}

</code>

and the following 2 protected methods were added to HibernateDaoSupport:

<code>
protected List list(Class domeinObject) {
CriteriaImpl crit = getHibernateTemplate().getDetachedCriteria(domeinObject);
addCriteria(crit);
return getHibernateTemplate().find(crit);
}

protected Criteria addCriteria(Criteria criteria) {
	return criteria;
}

</code>

now my developers can override addCriteria and call list with their domain object in implementing classes.

I have identified 2 major drawbacks to this approach:

1. each implementing class can implement addCriteria only once, thus a State pattern is neccessary to perform different list calls.
2. the explicit cast to SessionImpl that is needed because CriteriaImpl requires it in the setSession function

I hope this functionality will be added in the near future.
Yours sincerely,

Frank Verbruggen

---

Affects: 1.2 final

[spring-projects-issues]

Juergen Hoeller commented

The problem that I see is that the Hibernate Criteria API itself is not intended for detached use. There is a separate DetachedCriteria API available (org.hibernate.criterion.DetachedCriteria), which allows creation of DetachedCriteria objects without a Session (for example, at DAO initialization, to be kept in instance variables). Such DetachedCriteria objects can then be executed through the "DetachedCriteria.getExecutableCriteria(Session)" method, where you pass in a Session and get a standard Criteria object back that you can call "list()" or the like on.

To execute such a DetachedCriteria object with Spring's HibernateTemplate, you need to use a custom HibernateCallback implementation where you call "DetachedCriteria.getExecutableCriteria(Session)" on the passed-in Session. On this occasion, I consider adding a corresponding convenience find method to HibernateTemplate itself, where you could simply pass in a DetachedCriteria object - avoiding the need for a custom HibernateCallback implementation.

Juergen

[spring-projects-issues]

Frank Verbruggen commented

Juergen,

we make subset selections of our records,
thus we need these two functions of CriteriaImpl:

public Criteria setMaxResults(int maxResults) {
	this.maxResults = new Integer(maxResults);
	return this;
}

public Criteria setFirstResult(int firstResult) {
	this.firstResult = new Integer(firstResult);
	return this;
}

they do not appear in DetachedCriteria, thus it does not serve our needs.

[spring-projects-issues]

Frank Verbruggen commented

PS I forgot

prepareCriteria(detachedCriteria);

in my find function

[spring-projects-issues]

Juergen Hoeller commented

I have added "findByCriteria(DetachedCriteria)" and "findByCriteria(DetachedCriteria, firstResult, maxResults)" methods to HibernateTemplate. This allows for convenient use of DetachedCriteria objects with HibernateTemplate, even when only loading a subset of the result.

As I indicated, detaching Criteria objects directly is not intended on the Hibernate side, hence we won't support it in Spring either. Spring does not work with SessionImpl or any other internal Hibernate classes and won't start to do so, as it is not guaranteed that those methods will be backwards compatible even between Hibernate point releases.

If you want "setFirstResult" and "setMaxResults" methods for proper detached use on DetachedCriteria, raise an enhance request at the Hibernate JIRA. A Hibernate enhancement is the proper place to address this, not a Spring enhancement.

For now, the overloaded "findByCriteria" variant on HibernateTemplate should be fine as well: After all, concrete subset indexs are usually determined by dynamic parameters anyway, so couldn't be held in a shared DetachedCriteria instance in the first place.

Juergen

[spring-projects-issues]

Frank Verbruggen commented

Thx Juergen for the great help