ClassCastException with hibernate

Question

I am trying to fetch specific fields from my entities. I need the result in my entity structure.

Following are my entities:

Country

public class CountryModel {

    @Id
    @GeneratedValue(strategy = GenerationType.AUTO)
    @Column(name = "CmtID")
    private int id;
    @Column(name = "CmtName")
    private String name;
    @JoinColumn(name="CmtStateID")
    @OneToMany(targetEntity=StateModel.class,fetch=FetchType.EAGER)
    private List<StateModel> state;
}

State

public class StateModel {
    @Id
    @GeneratedValue(strategy = GenerationType.AUTO)
    @Column(name = "SmtID")
    private int id;
    @Column(name = "SmtName")
    private String name;
}

Following is the HQL query am executing:

Query query = session.createQuery("select c.name, s.name from CountryModel c join c.state s where c.id=2");
CountryModel stateModel = (CountryModel) query.uniqueResult();

But am getting the following error:

java.lang.ClassCastException: [Ljava.lang.Object; cannot be cast to com.muziris.entity.CountryModel

Thanks for helping.

Expected result:

Country :
        name : india
        state : 
              name : kerala
              name : goa
        name : Pak
        state :
              name : karachi

Answer 1

Since your classes are mapped you can try:

 Query query = session.createQuery("from CountryModel c where c.id=2");
 CountryModel countryModel = (CountryModel) query.uniqueResult();

Let's make use of the mapping and HQL.

From there you can use a DTO to have only the data that you need

public CountryDTO transform(CountryModel cm){
String countryName = cm.getName();
List<String> stateNames = cm.getState().stream.map(StateModel::getName)
                                              .collect(Collectors.toList());
return new CountryDTO(countryName, stateNames);
}

CountryDTO is the result that you need.

Answer 2

Hibernate returns List<Object[]> when you use the projections. List<Object[]> is a list of specified projection columns.

Some links

https://stackoverflow.com/a/36883968/3405171

How to transform a flat result set using Hibernate