How to cast from a list<Objects> when using Hibernate query language?

Question

I've been working on a hibernate/JPA project, and during the development i have created a method to retrieve a list of an object called Appel_Offre.java, and in the run time an exception occurred... Here is the method: I have an object Appel_Offre.java and another object called Modalite_Appel_Offre.java here is the mapping of the two objects: Appel_Offre.java

     @Entity
     @Table(name="Appel_offre")
     public class Appel_Offre {

@Id
@Column(name="num_app_offre",nullable=false, updatable=true)
private String num_app_offre;

@Column(name="nom_maitre",nullable=false, updatable=true)
private String nom_maitre;

@Column(name="objet",nullable=false, updatable=true)
private String objet;

@Column(name="date_depot",nullable=false, updatable=true)
@Temporal(TemporalType.TIMESTAMP)
private Date date_depot;

@Column(name="date_soumission",nullable=false, updatable=true)
@Temporal(TemporalType.DATE)
private Date date_soumission;

@Column(name="garantie",nullable=false, updatable=true)
private int garantie;

@Column(name="delai_livraison",nullable=false, updatable=true)
private int delai_livraison;

@Column(name="caution_provisoir_total",nullable=false, updatable=true)
private float caution_provisoir_total;

@Column(name="commentaire",nullable=false, updatable=false)
private String commentaire;

@Column(name="etat",nullable=false, updatable=true)
private String etat;

@OneToMany(targetEntity=Lot.class,mappedBy="appel_offre", cascade= CascadeType.PERSIST,fetch= FetchType.LAZY)
private List<Lot>  lots;

@OneToMany(targetEntity=Modalite_Appel_Offre.class,mappedBy="ao", cascade= CascadeType.PERSIST,fetch= FetchType.EAGER)
private List<Modalite_Appel_Offre>  mod;

Modalite_Appel_Offre.java :

    @Entity
    @Table(name="Modalite_appel_offre")
    public class Modalite_Appel_Offre {

@Id
@TableGenerator(name="mod_id", table="modalite_id",pkColumnName="id_mod",        pkColumnValue="value of the id",allocationSize=1)
@GeneratedValue(strategy= GenerationType.TABLE, generator="mod_id")
private int id_mod;

@Column(name="nom_modalite")
private String nom_mod;

@ManyToOne
@JoinColumn(name="ao")
private Appel_Offre ao;
 //Getters & Setters

In my method i want to retrieve the list of Appel_Offre by Modalite_Appel_Offre.nom_mod here is the code :

    public static List<Appel_Offre> getAppelOffreByModalite(Modalite_Appel_Offre mod){
    List <Appel_Offre> lm=null;
    try{
         session=sf.openSession();
    session.beginTransaction();
     lm=(List <Appel_Offre>)session.createQuery("from Appel_Offre m , Modalite_Appel_Offre mod where mod.nom_mod= ?").setString(0, mod.getNom_mod()).list();
    }
   catch(Exception e){

   }
    finally{
        session.close();
    }
    return lm;
}

and when i loop on the returned list :

     int i = 0;
    for (Appel_Offre ap : lap) {
        data[i][0] = ap.getNum_app_offre();
        data[i][1] = ap.getNom_maitre();

        i++;
    } //data is an array of String

An exception occurred :

    java.lang.ClassCastException: [Ljava.lang.Object; cannot be cast to gest.BO.Appel_Offre

What i didn't understand is i am looping on a list of Appel_Offre, and the loop type is Appel_Offre why would hibernate trigger this exception? Thank you.

David Lavender · Accepted Answer · 2013-02-04 15:25:55Z

1

I think it is your query:

from Appel_Offre m , Modalite_Appel_Offre mod where mod.nom_mod= ?

That is not just asking for Appel_Offre instances... it is asking for Appel_Offre joined to Modalite_Appel_Offre (you have multiple tables in the FROM clause). So, Hibernate is making you a weird List, which will be a compound join of those two tables: not just Appel_Offre instances. I may have misunderstood what the query is supposed to do. But, anyway, you only want Appel_Offre in the FROM clause. Something like:

from Appel_Offre where m.ao = ?

answered Feb 4, 2013 at 15:25

David Lavender

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2 Comments

David Lavender Over a year ago

Hmm, actually, re-reading I would expect class cast to be on line (List <Appel_Offre>)session.createQuery...

Zakaria Marrah Over a year ago

I changed the query to "from Appel_Offre m where m.nom_mod= ?" but i have an NPE when looping on the list.

kosa · Accepted Answer · 2013-02-04 15:25:04Z

0

One cleaner way to resolve this issue would be using addEntity and this.

Example:

List cats = session.createSQLQuery(
    "SELECT {cat}.ID AS {cat.id}, {cat}.SEX AS {cat.sex}, " +
           "{cat}.MATE AS {cat.mate}, {cat}.SUBCLASS AS {cat.class}, ... " +
    "FROM CAT {cat} WHERE ROWNUM<10")
    .addEntity("cat", Cat.class)
.list()

If you don't want to use approach, I think only way you could do is, get List and iterate and construct the object type you want.

answered Feb 4, 2013 at 15:25

kosa

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