How to get subclasses attributes using SingleTableInheritance with SpringMVC

Question

i am working on a web application using Spring, Hibernate and SpringMVC, i am facing a problem with retreiving values from a subclass table using SingleTable inheritance strategy, here are my entities

Client.java (Super class)

    @Entity
    @Inheritance(strategy = InheritanceType.SINGLE_TABLE)
    @DiscriminatorColumn(name = "typeClient", discriminatorType = DiscriminatorType.STRING)
    public class Client implements Serializable {

        @Id
        @GeneratedValue(strategy = GenerationType.IDENTITY)
        private int idClient;

        private String matricule;
        private String statut;

        private String secteurDactivite;
        private String nomClient;


        private String emailClient;

        private String numTelephone;

        private String adresse;
//constructor
//getter & setters
     }

Societe.java (subClass1)

@Entity
@DiscriminatorValue("Societe")
public class Societe extends Client implements Serializable{


    private String nomResponsable;


    private String emailResponsable;


    private String telResponsable;


    private String nomSuperieur;


    private String emailSuperieur;


    private String telSuperieur;

    private String commentaire;

    //constructeur sans parametre
    public Societe() {
        }
    }

Particulier.java (subclass2)

@Entity
@DiscriminatorValue("Particulier")
public class Particulier extends Client implements Serializable {

    private String cin;


    //constructeur sans parametres
    public Particulier() {

    }
    }

in my implementation i am using this methode to get a particular client with his ID

ClientDaoImpl.java

public class ClientDaoImpl implements ClientDao {
    @PersistenceContext
    private EntityManager em;

    @Override
    public Client getClientByID(int id_client) {
        return em.find(Client.class, id_client);
    }

When i ran this code i only selected the attributes of the superClass Client .

what i am trying to do is to get a client with its subclass whether it's a Societe or Particulier based on its type or clientID.

Please Help

Answer 1

As you don't know the type of client before querying and only it's ID, you will need to inspect the type and cast after you retrieve the record;

Client client1 = clientDao.getClientById(clientID);
if (client1 instanceof Societe) {
    ((Societe) client1).getCommentaire();
}

Depending on your use case, it may be useful to map the result of the client query to a ClientDescriptor object which contains all the fields for all client types and returns either nulls or blanks. This means you don't have to keep checking for client type everywhere;

public class ClientDTO {
    //client fields
    private String nomResponsable = "";
    ....
    //subclass 1 fields.... initialize to empty
    //subclass 2 fields .... initialize to empty

    public ClientDTO (Client client) {
        // set fields for client entity
    }

    public ClientDTO (Societe societe) {
        this (societe);
        // set societe fields.
    }
    // other constructors.
}

Answer 2

You can modify your getClientByID method to accept an additional argument which will say what type of entity your want to retrieve and get back:

public class ClientDaoImpl implements ClientDao {
    @PersistenceContext
    private EntityManager em;

    public <T extends Client> T getByID(int id_client, Class<T> klass) {
        return em.find(klass, id_client);
    }
}

And you can use this dao in the following manner:

Societe societe = clientDao.getByID(42, Societe.class);
Particulier particulier = clientDao.getByID(43, Particulier.class);