Question

I’m retrieving a list of rows with selected fields from Oracle database using Hibernate. The retrieval is made by the following method in one of the DAOs in my application.

@SuppressWarnings("unchecked")
public List<Object[]> getOldFileName(String []ids)
{
    int len=ids.length;
    Long longType[]=new Long[len];

    for(int i=0;i<len;i++)
    {
        longType[i]=Long.valueOf(ids[i]);
    }
    return sessionFactory.getCurrentSession().createQuery("select catId, catImage from Category where catId in(:id)").setParameterList("id", longType).list();
}

Here I’m fetching two fields categoryId and categoryImage as listed in the given HQL query based on the catId supplied as an array of String[] as a method parameter via Spring. It works fine and there is no question about it.

But regarding my requirements, retrieving catId again is completely unnecessary and I would like to remove catId from the list of fields in the query something simply like the following.

select catImage from Category where catId in(:id)

If I try to execute this query then the following call to the preceding method inside the Spring controller class,

String temp[]=request.getParameter("setDel").split(",");
List<Object[]> oldFileNames = categoryService.getOldFileName(temp); 
//Invokes the preceding method in DAO.

causes the following exception to be thrown,

java.lang.ClassCastException: java.lang.String cannot be cast to
[Ljava.lang.Object;

The exception message indicates that java.lang.String cannot be cast to an array of Objects – Object[]. It appears that the HQL statement attempts to get only a single value of type String instead of retrieving List<Object[]>.

I just want to delete files which are stored in a directory after retrieving their names from the database and mentioning of catId in the list of fields in HQL is completely unnecessary.

Why do I need to add catId in the list of fields of the HQL statement in this scenario?

Answer 1

The return type for the list should be List. When only one column comes back hibernate does not put the result into and Object[]