Generic implementation for named queries execution

Question

I am trying to implement a generic class (GenericDaoImpl<T,E>) which contains a method that executes NamedQueries (findByNamedQuery(..)). This method asks for a named query name and and an object array (parameters). I must iterate them and bind these parameters to the named query.

I can not change the method signature.

public abstract class GenericDaoImpl<T, E> implements GenericDao<T, E> {

    @PersistenceContext(unitName="MyUnit")
    protected EntityManager em;
    private Class<T> persistentClass;

    @SuppressWarnings("unchecked")
    public GenericDaoImpl() {
        this.persistentClass = getPersistentClass();
    }

    public void setPersistentClass(Class<T> persistentClass) {
        this.persistentClass = persistentClass;
    }

    public Class<T> getPersistentClass() {
        Class<?>[] typeArguments = TypeResolver.resolveRawArguments(GenericDao.class, getClass());
        this.persistentClass = (Class<T>) typeArguments[0];
        return persistentClass;
    }

    ....

    @Transactional
    public void save(T entity) {
        em.persist(entity);
    }

    @Transactional
    public void update(T entity) {
        em.merge(entity);
    }

    @Transactional
    public void delete(E id) {
        em.remove(em.find(persistentClass,id));
    }

    ...

    public List<T> findByNamedQuery(String queryName, Object... params) {
        Query q = this.em.createNamedQuery(queryName,persistentClass);
        for(int i =1;i<params.length-1;i++){
            q.setParameter(i, params[i]);
        }
        return (List<T>)q.getResultList();
    }

}

Now, given this named query:

@NamedQuery(name="Office.findByStreetAndCity",query="SELECT o from Office o JOIN o.address a WHERE a.street=:street AND a.city=:city"),

Let's execute the method:

String[] params= {"Mount Eden Road", "London"};
List<Office> offices= dao.findByNamedQuery("Office.findByStreetAndCity", params);

But it fails:

java.lang.IllegalArgumentException: org.hibernate.QueryException: Not all named parameters have been set: [city, street] [SELECT o from Office o JOIN o.address a WHERE a.street=:street AND a.city =:city]

I am not very familiar with JPA but I think that this is failing because we can not set parameters by index when using named parameters on NamedQuery definition.

Answer 1

Your assumption is correct, and you're mixing between the two.

You can either continue using setParameter("street", "Mount Eden Road") and change your signature to something like public List<T> findByNamedQuery(String queryName, Map<String, Object> params) or rewrite your query to use positional parameters (starting from 0):

SELECT o from Office o JOIN o.address a WHERE a.street=? AND a.city=?

for(int i = 0; i < params.length; i++){
    q.setParameter(i, params[i]);
}