How to return a list of specific type instead of List<Object[]> in Hibernate?

Question

I have tree of classes:

classA {  
      classB b;  
      classC c;
      .....
} 

I have HQL query like this:

Answer 1

You can use TypedQuery

TypedQuery<ClassA> q = em.createQuery("select a from a left outer join b on a.id=b.fk left outer join c on b.id=c.fk", ClassA.class); 
List<ClassA> res = q.getResultList(); 

Answer 2

i had same problem..i wrote this query

Query sqlquery = session.createQuery("select c.courseName,f.facultyID,f.facultyName,f.facultyEmailID,f.facultyContactNo,s.subjectName from com.bean.CourseBean as c,com.bean.FacultyBean as f,com.bean.Faculty_SubjectBean as fs,com.bean.SubjectBean as s where f.facultyID=fs.facultyBean.facultyID AND s.subjectID=fs.subjectBean.subjectID AND c.courseID=f.courseBean.courseID AND collegeid=1");

and i returned list of object and in servlet i wrote,

java.util.List objList= objFacultyService.listFaculty_sql(1);

java.util.List<Temp> objtemp = new ArrayList<Temp>() ;
for (Object[] objects : objList)
{


        Temp temp = new Temp();
        temp.setFacultyEmailID(objects[3].toString());
        temp.setCourseName(objects[0].toString());
        if(objects[4]==null)
        {
            temp.setFacultyContactNo(1);
        }
        else
        {
                  temp.setFacultyContactNo(Long.parseLong(objects[4].toString()));
        }
        temp.setFacultyID(Long.parseLong(objects[1].toString()));
        temp.setFacultyName(objects[2].toString());
        temp.setSubjectName(objects[5].toString());
        objtemp.add(temp);




}

Answer 3

There are different types of selects in JPA queries. You are currently using Array as a return type, what you need is Construct return type. Here is how to achieve this:

String queryStr =
    "select NEW package.YourDefinedCustomClass(
     a.field1, b.field2, c.field3, c.field4) from a left outer join b 
     on a.id=b.fk left outer join c on b.id=c.fk";

TypedQuery<YourDefinedCustomClass> query =
    em.createQuery(queryStr, YourDefinedCustomClass.class);

List<YourDefinedCustomClass> results = query.getResultList();

Basically there are two things:

1. Custom class must be your results return type
2. Custom class must have a constructor which takes result values you define in query string.

Read more on selects in JPA2 queries.

Answer 4

If you are really sure you can do type casts.

 List<classD> newlist = ...;
 for(Object o : list){
      newlist.add((classD) o);
 }

Be careful with this though

So yes. Manual casting. (note: with arrays (you can directly cast) )

Answer 5

If you use Hibernate 5.x, you can use a ResultTransformer, as, e.g., described in this blog post. Note that ResultTransformer will be @Deprecated in Hibernate 6.

Applied to your scenario:

List<classD> classDDTOs = entityManager
.createQuery(
    "SELECT a.field1, b.field2, c.field3, c.field4 " +
    "FROM a LEFT OUTER JOIN b ON a.id = b.fk " +
    "LEFT OUTER JOIN c ON b.id = c.fk")
.unwrap( org.hibernate.query.Query.class )
.setResultTransformer( 
    new ResultTransformer() {
        @Override
        public Object transformTuple(
            Object[] tuple, 
            String[] aliases) {
            return new classD(
                (Type1) tuple[0],
                (Type2) tuple[1],
                (Type3) tuple[1],
            );
        }

        @Override
        public List transformList(List collection) {
            return collection;
        }
    } 
)
.getResultList();

The above code assumes classD has a constructor classD(Type1, Type2, Type3).

An advantage of this approach is that it lets you define the ResultTransformer once and allows you to reuse it in all queries with the same result type.