I am developing a Java web application using Hibernate and JSF/primefaces. am sometimes getting errors like
1) an object with same identifier is already associated with session.
2) failed to load lazy initialization *,no session exist or session is already closed.
I know this is due to improper coding in my app. this is the way am doing aap:
When a user requests for a page(Let it be a list of Employees). the user will get the employee list page(empployeeList.xhtml) EmployeeListMBean is the managed bean for this page. in the managed bean in the constructor, am calling a method populateEmployees(). populateEmployee() will use the EmployeeDao method getAllEmployee() to getAllemployees.
Employee Class goes here:
@Entity
@Table(name = "Employee")
@NamedQueries({
@NamedQuery(name = "Employee.getAllEmployee", query = "from Employee"),
@NamedQuery(name = "Employee.findEmployeeByFirstName", query = "from Employee where firstName = :firstName"),
@NamedQuery(name = "Employee.findEmployeeByLastName", query = "from Employee where lastName = :lastName"),
@NamedQuery(name = "Employee.findEmployeeByMiddleName", query = "from Employee where middleName = :middleName"),
@NamedQuery(name = "Employee.findEmployeeByOffice", query = "from Employee where office.id = :officeId")
})
public class Employee implements Serializable {
@Id
@GeneratedValue(strategy = GenerationType.AUTO)
@Column(name = "EID")
private long id;
@Column(name = "FIRST_NAME")
private String firstName;
@Column(name = "LAST_NAME")
private String lastName;
@Column(name = "GENDER")
private String gender;
@Column(name = "DOB")
@Temporal(javax.persistence.TemporalType.DATE)
private Date dateOfBirth;
@Column(name = "DOH")
@Temporal(javax.persistence.TemporalType.DATE)
private Date dateOfHire;
@ManyToOne(cascade= CascadeType.ALL)
private Office office;
@OneToOne(cascade = CascadeType.ALL)
private ResidenceAddress residence;
@OneToMany
private List<Project> projects;
//getters and setters
}
here is my EmployeeDao:
public class EmployeeDao implements Serializable{
private SessionFactory factory;
private Session session;
public void addEmployee(Employee employee){
factory = HibernateUtil.getSessionFactory();
session = factory.openSession();
session.beginTransaction();
session.save(employee);
session.getTransaction.commit();
}
public List<Employee> getAllEmployee(){
factory = HibernateUtil.getSessionFactory();
session = factory.openSession();
session.beginTransaction();
List<Employee> cities = session.getNamedQuery("Employee.getAllEmployee").list();
session.close();
return cities;
}
public Employee getEmployeeByEmployeeId(long employeeId){
factory = HibernateUtil.getSessionFactory();
session = factory.openSession();
session.beginTransaction();
Employee employee = (Employee) session.get(Employee.class, employeeId);
session.close();
return employee;
}
}
Question 1) here, in the methods I am closing the session and then return back the result to managedbeans. so in the employee listing page the table list out name dob dateOfHire. and I have a buutton view more detail. on clicking this button, I want to display all projects of selected employee working on using the same managedbeans but, it is giving me error(2), failed to lazyload, no session or session already closed. if I keep the session opened in the getemployeeMethod of dao, I guess that may lead to a memory leak problem, or someother problem. is it so? also, I have tried lazy and eager loading. please give me a clear idea when/how to use these type of fetching. How can I solve this? can I go for filters or facelisteners for solving this?
Question 2) if am trying to edit a project of an employee, and update using session.saveorupadte(), merge(),flush(), am getting an error like this, "an object with same identifier is already associated with session" How can I solve this?
Question 3) I know that sessionfactory is resource consuming. so only single instance is enough for one app. but what about session? for a SINGLE USER of app, only one session is needed? please tell me good strategy for developing such an app.
Thanking you all :)