Hibernate currently has some issues with Restrictions.in.  Basically if you try to pass it NULL it generates invalid SQL on at least MySQL and PostgreSQL.  I found a blog post outlining how to fix this issue and the accompanying JIRA issue which confirms that I’m not the only one having this problem.  Unfortunately this person’s fix didn’t work for me but I think that’s because they’re using MySQL and I’m using PostgreSQL.  Differences in the driver still make this fail on PostgreSQL.

In order to remedy this I set out to find a better solution that would hopefully work on Hibernate with any backend.  What I came up with, with some help from StackOverflow, is this:

public static <M> void addInRestriction(DetachedCriteria dc, String idDbField, List ids) {
    // Is our list empty?
    if ((ids != null) && (ids.size() > 0)) {
        // No, add this restriction to the detached object
        dc.add(Restrictions.in(idDbField, ids));
    } else {
        // Yes, our list is empty.  Make this always fail.
        // From: http://stackoverflow.com/questions/2667131/is-there-something-like-restrictions-eqtrue-false-in-criteria-api
        dc.add(Restrictions.sqlRestriction("(1=0)"));
    }
}

I put this in a class with some other Hibernate helper functions and now instead of doing this:

dc.add(Restrictions.in("fieldName", fieldValues));

I do this:

HibernateQueryUtils.addInRestriction(dc, "fieldName", fieldValues);

This fixed all of my Hibernate issues when passing it a NULL or even an empty list. Hope it works for you too!