Question

How can I set a Hibernate Parameter to “null”? Example:

Query query = getSession().createQuery("from CountryDTO c where c.status = :status  and c.type =:type")
.setParameter("status", status, Hibernate.STRING)
.setParameter("type", type, Hibernate.STRING);

In my case, the status String can be null. I have debugged this and hibernate then generates an SQL string/query like this ….status = null… This however does not Work in MYSQL, as the correct SQL statement must be “status is null” (Mysql does not understand status=null and evaluates this to false so that no records will ever be returned for the query, according to the mysql docs i have read…)

My Questions:

1. Why doesnt Hibernate translate a null string correctly to “is null” (and rather and wrongly creates “=null”)?

2. What is the best way to rewrite this query so that it is null-safe? With nullsafe I mean that in the case that the “status” String is null than it should create an “is null”?

Answer 1

1. I believe hibernate first translates your HQL query to SQL and only after that it tries to bind your parameters. Which means that it won’t be able to rewrite query from param = ? to param is null.

2. Try using Criteria api:

   Criteria c = session.createCriteria(CountryDTO.class);
   c.add(Restrictions.eq("type", type));
   c.add(status == null ? Restrictions.isNull("status") : Restrictions.eq("status", status));
   List result = c.list();