Hibernate: How to set NULL query-parameter value with HQL?

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(); 

Answer 2

This is not a Hibernate specific issue (it's just SQL nature), and YES, there IS a solution for both SQL and HQL:

@Peter Lang had the right idea, and you had the correct HQL query. I guess you just needed a new clean run to pick up the query changes ;-)

The below code absolutely works and it is great if you keep all your queries in orm.xml

from CountryDTO c where ((:status is null and c.status is null) or c.status = :status) and c.type =:type

If your parameter String is null then the query will check if the row's status is null as well. Otherwise it will resort to compare with the equals sign.

Notes:

The issue may be a specific MySql quirk. I only tested with Oracle.

The above query assumes that there are table rows where c.status is null

The where clause is prioritized so that the parameter is checked first.

The parameter name 'type' may be a reserved word in SQL but it shouldn't matter since it is replaced before the query runs.

If you needed to skip the :status where_clause altogether; you can code like so:

from CountryDTO c where (:status is null or c.status = :status) and c.type =:type

and it is equivalent to:

sql.append(" where "); if(status != null){   sql.append(" c.status = :status and "); } sql.append(" c.type =:type ");