Hibernate unidirectional one-to-one mapping - sql

Question

I have the following table structure.
(The unique constraint is to avoid multiple 'details' to the same employee - I can't change the db structure).
https://i.ibb.co/r3pYQFj/fk.png
create table employee (
employee_id number(19),
salary number(10),
constraint pk_employee primary key (employee_id)
);
create table employee_details (
employee_details_id number(19),
employee_id number(19) not null,
address varchar2(256),
gender char(1),
constraint fk_employee foreign key (employee_id) references employee (employee_id),
constraint fk_employee_unq unique (employee_id)
);
Model class:
#Entity
#Table(name = "EMPLOYEE")
public class Employee implements Serializable {
#Id
#GeneratedValue(strategy = GenerationType.SEQUENCE, generator = "empgen")
#SequenceGenerator(name = "empgen", sequenceName = "SEQ_EMP", allocationSize = 1)
#Column(name = "EMPLOYEE_ID")
private Long id;
#OneToOne(fetch = FetchType.LAZY, cascade = CascadeType.ALL)
#JoinColumn(name="EMPLOYEE_ID")
private EmployeeDetail empDetail;
...
#Entity
#Table(name = "EMPLOYEE_DETAIL")
public class EmployeeDetail implements Serializable {
#Id
#GeneratedValue(strategy = GenerationType.SEQUENCE, generator = "empdetgen")
#SequenceGenerator(name = "empdetgen", sequenceName = "SEQ_EMP_DET", allocationSize = 1)
#Column(name = "EMPLOYEE_DETAILS_ID")
private Long id;
#Column(name = "EMPLOYEE_ID")
private Long employeeId;
...
I have a rest controller that receive a JSON like this:
{
"employee": {
"salary": 80000,
"empDetail": {
"adress": "ST EXAMPLE",
"gender": "M"
}
}
}
I'm trying to persist all the entities via hibernate (5.4.28) saving Employee as the first entity, then with its primary key, EmployeeDetails using it's parent primary key but I get this:
java.sql.SQLIntegrityConstraintViolationException: ORA-01400: cannot insert NULL into ("DCC"."EMPLOYEE_DETAILS"."EMPLOYEE_ID")
Why it's trying to save the child before the parent?
How the the class should be mapped?

Answer 1

I guess it's because Hibernate thinks that by putting #JoinColumn on Employee.empDetail, EMPLOYEE_ID belongs to the employee_details table.
Try putting creating a property EmployeeDetail.employee and put #JoinColumn on that one. If you need a reference from Employee, use #OneToOne(mappedBy=...).
How to use #JoinColumn
Activate logging to see which statements are executed