I have a many to one relationship and I am trying to persist a child entity.
public class Office
{
public int id;
public int grades;
@OneToMany
public set<Employee> employees;
}
public class Employee{
@GeneratedValue(strategy=GeneratedValue.identity)
public int empid;
@ManyToOne(cascade=cascadeType.ALL)
public Office office;
}
Office Id is already present in the database. But employee is not.
Now if i am adding an employee and his grades must go into the office database.
When i do the following operation,grades are not getting saved
Office office = new Office();
office.setId(23);
office.setGrades(5);
employee.setOffice(office);
em.persist(employee);
How to save grades into the office table in a single operation
First, fix your mapping.
The association is bidirectional, and one of the side (the one side) must be marked as the inverse of the other using the mappedBy attribute:
@OneToMany(mappedBy = "office")
public set<Employee> employees;
The employee is only one of the employees of the office. Do you really want to delete the entire office when you delete a single employee? If not, why do you put a cascade=cascadeType.ALL on the @ManyToOne? Those annotations have consequences. Don't use them without understanding them.
Now to really answer the question. If the office already exists in the database, you should not build a new one. Go fetch it from the database and update it:
Office office = em.find(Office.class, 23);
// office is now attached, and any change you make on the entity will be written to the database
office.setGrade(5);
Now you may also attach the office to the new employee. But since it's a bidirectional relationship, you should also initialize the other side of the association to keep the object graph coherent:
employee.setOffice(office);
office.addEmployee(employee);
em.persist(employee);
