Question

While I try to save top level entity (using JPA), do I need to get the ManyToOne mapped entity freshly from database and set it or cannot I just set Id (of manyToOne mapped entity and save top level entity?
When do not get fresh entity it throws: org.hibernate.TransientObjectException:

Table structures we are using:

DEPARTMENT(DEPARTMENT_ID BIGINT, NAME VARCHAR(128))

EMPLOYEE(EMPLOYEE_ID BIGINT, NAME VARCHAR(128), DEPARTMENT_ID BIGINT)

Entities:
class Department
{
   @Id
   Long departmentId;
   String name;
   @Version
   Long versionNumber;
}

class Employee
{
   @Id
   Long employeeId;
   String name;
   @ManyToOne
   Department department;
   @Version
   Long versionNumber
}

(both classes have setter and getter methods for all fields and default constructor, constructor which takes primary key as argument)
Now if I want to save Employee with departmentId (say 100), do I need to get the Department record first and then set it in employee?

Cannot I create instance of Department directly (by setting primary key(departmentId)) and set Department instance in Employee and save Employee?
When I do this it is throwing org.hibernate.TransientObjectException.

Any suggestions on best practice to be followed for this?

Thank you in advance

Answer 1

Thank you ChssPly76 and Wysawyg.

One of the solution could be:
We will update Employee POJO as below

ManyToOne(fetch=FetchType.EAGER)
@**JoinColumn**(name = "DEPARTMENT_ID", referencedColumnName = "DEPARTMENT_ID", **insertable=false, updatable=false**)
private Department department;

@Column(name = "department_id")
private Long departmentId;

(both department and departmentId will have setter and getter methods)

and Now here (please see that both department and departmentId mapped to same column (DEPARTMENT_ID)
we use department only for fetching Department details
and departmentId to insert or update Employee

But I am worried if it is a better approach.