JPA is'nt able to create ( persist ) an EJB - jpa

Question

Now two days trying to fix this problem.
The problem seems to come from the DAO class.
Caused by: projet.helpdesk.dao.DAOException: Exception [EclipseLink-4002] (Eclipse Persistence Services - 2.6.1.v20150605-31e8258): org.eclipse.persistence.exceptions.DatabaseException
Internal Exception: java.sql.SQLSyntaxErrorException: ORA-02289: sequence does not exist
Error Code: 2289
Call: SELECT SEQ_GEN_IDENTITY.NEXTVAL FROM DUAL
Query: ValueReadQuery(sql="SELECT SEQ_GEN_IDENTITY.NEXTVAL FROM DUAL")
at projet.helpdesk.dao.UserDao.creer(UserDao.java:25)
This is the entity:
package projet.helpdesk.beans;
import java.sql.Timestamp;
import javax.persistence.*;
#Entity
#Table(name = "Users")
public class Utilisateur {
#Column(name = "nom")
private String nom;
#Column(name = "prenom")
private String prenom;
#Column(name = "email")
private String email;
#Column(name = "departement")
private String dept;
#Column(name = "poste")
private String poste;
#Column(name = "agence")
private String agence;
#Column(name = "mdp")
private String mdp;
#Column(name = "type")
private String type;
#Column(name = "date_inscr")
private Timestamp date_inscr;
#Id
#GeneratedValue( strategy = GenerationType.IDENTITY )
#Column(name = "id_emp")
private int idemp;
public String getNom() {
return nom;
}
public void setNom(String nom) {
this.nom = nom;
}
public String getPrenom() {
return prenom;
}
public void setPrenom(String prenom) {
this.prenom = prenom;
}
public String getEmail() {
return email;
}
public void setEmail(String email) {
this.email = email;
}
public String getDept() {
return dept;
}
public void setDept(String dept) {
this.dept = dept;
}
public String getPoste() {
return poste;
}
public void setPoste(String poste) {
this.poste = poste;
}
public String getAgence() {
return agence;
}
public void setAgence(String agence) {
this.agence = agence;
}
public int getIdemp() {
return idemp;
}
public void setIdemp(int id) {
this.idemp = id;
}
public String getMdp() {
return mdp;
}
public void setMdp(String mdp) {
this.mdp = mdp;
}
public String getType() {
return type;
}
public void setType(String type) {
this.type = type;
}
public Timestamp getDate_inscr() {
return date_inscr;
}
public void setDate_inscr(Timestamp date_inscr) {
this.date_inscr = date_inscr;
}
}
EDIT: Error occurs when executing query.
This is the Stacktrace:
Caused by: java.lang.IllegalArgumentException: An exception occurred while creating a query in EntityManager:
Exception Description: Problem compiling [SELECT u FROM Users u WHERE u.email=:email].
[14, 19] The abstract schema type 'Users' is unknown.
[28, 35] The state field path 'u.email' cannot be resolved to a valid type.
at org.eclipse.persistence.internal.jpa.EntityManagerImpl.createQuery(EntityManagerImpl.java:1616)
at com.sun.enterprise.container.common.impl.EntityManagerWrapper.createQuery(EntityManagerWrapper.java:456)
at projet.helpdesk.dao.UserDao.trouver(UserDao.java:32)
The error comes from the method "trouver"
#Stateless
public class UserDao {
private static final String JPQL_SELECT_PAR_EMAIL = "SELECT u FROM Users u WHERE u.email=:email";
private static final String PARAM_EMAIL = "email";
This is the method "trouver"
public Utilisateur trouver( String email ) throws DAOException {
Utilisateur utilisateur = null;
Query requete = em.createQuery( JPQL_SELECT_PAR_EMAIL );
requete.setParameter( PARAM_EMAIL, email );
try {
utilisateur = (Utilisateur) requete.getSingleResult();
} catch ( NoResultException e ) {
return null;
} catch ( Exception e ) {
throw new DAOException( e );
}
return utilisateur;
}
knowing that the table Users is declared.
This is the bean Utilisateur.
#Entity
#Table(name = "Users")
public class Utilisateur {...

Answer 1

The message tells clearly what the problem is:
Internal Exception: java.sql.SQLSyntaxErrorException: ORA-02289: sequence does not exist
sql="SELECT SEQ_GEN_IDENTITY.NEXTVAL FROM DUAL")
The code is trying to read from a database sequence named "SEQ_GEN_IDENTITY", but this one doesn't exist.
I'm not sure why this, you have this in your code:
#GeneratedValue( strategy = GenerationType.IDENTITY )
This should tell JPA that it should use the database identity column to get the ID for the object it wants to persist.
If you don't have a specific reason to use GenerationType.IDENTITY, you should change it to GenerationType.SEQUENCE.
To do that you have to change your class to look like this:
#Id
#GeneratedValue( strategy = GenerationType.SEQUENCE )
#Column(name = "id_emp")
private int idemp;
If you are using EclipseLink (default) you have to create a database sequence named "seq_gen_sequence". If you are using Hibernate you have to create a database sequence named "hibernate_sequence".
See also:
what is the use of annotations #Id and #GeneratedValue(strategy = GenerationType.IDENTITY)? Why the generationtype is identity?
#GeneratedValue(strategy=“IDENTITY”) vs. #GeneratedValue(strategy=“SEQUENCE”)
How to choose the id generation strategy when using JPA and Hibernate