I'm getting a org.hibernate.MappingException: Unknown entity: null error with this query


//subquery -Where clause subselect
DetachedCriteria subquery = DetachedCriteria.forClass(Book.class, "u");
subquery.createAlias("u.bookProfile", "xp", CriteriaSpecification.INNER_JOIN);
subquery.add(Restrictions.eqProperty("xp.bookName","stringabc"));
subquery.setProjection(Property.forName("u.createTimestamp"));

//outer query
Criteria c = session.createCriteria(Book.class, "i");
c.add( Subqueries.geAll("i.createTimestamp", subquery));

Thanks in advance !