how to add object with fk to table in jparepository - spring-boot

Question

i had scheme of user parking and detail parking.
user can park many times (one to many)
im trying to add detail parking object to my db, but i dont have idea how to add the fk from the user in the row of the table, its gave me null there.
(ignore from the logic of the model, i just want to understood the logic how can i the object with fk of ther entity)
this is my code:
#PostMapping("/parking")
public String saveCarParking(#ModelAttribute("user") parkingUsers parkingUsers) {
// parkingUsers[id, firstName, lastName, license]
parkingUsers p = new parkingUsers("jhon", "nash", "248651355");
parkingUsersService.saveParkingUser(p);
// parkingDetails[id, entryDate, entryTime, exitDate, exitTime, user_id(FK)]
parkingDetails d = new parkingDetails(LocalDate.now(), null, LocalDate.now(), null);
parkingDetailsService.saveParkingUser(d);
//how i connect parkingDetails object with fk of parkingUsers?
//it adding now row of parkingDetails but without the fk of user
return "redirect:/parkingList";
}
parking user entity:
#Entity
#Table(name ="users")
public class parkingUsers {
#Id
#GeneratedValue(strategy = GenerationType.IDENTITY)
#Column(name = "id")
private int id;
#Column(name = "first_name")
private String firstName;
#Column(name = "last_name")
private String lastName;
#Column(name = "license")
private String license;
#OneToMany(mappedBy = "parkingUsers", cascade = CascadeType.ALL, orphanRemoval = true)
private List<parkingDetails> parkingDetails = new ArrayList<parkingDetails>();
public parkingUsers() {
}
public parkingUsers(String firstName, String lastName, String license) {
this.firstName = firstName;
this.lastName = lastName;
this.license = license;
}
//setter gettrs and tostring...
entity class of details parking
#Entity
#Table(name ="details")
public class parkingDetails {
#Id
#GeneratedValue(strategy = GenerationType.IDENTITY)
#Column(name = "id")
private int id;
#Column(name = "entry_date")
private LocalDate entryDate;
#Column(name = "entry_time")
private LocalDateTime entryTime;
#Column(name = "exit_date")
private LocalDate exitDate;
#Column(name = "exit_time")
private LocalDateTime exitTime;
#ManyToOne
#JoinColumn(name="user_id")
private parkingUsers parkingUsers;
public parkingDetails() {}
public parkingDetails(LocalDate entryDate, LocalDateTime entryTime, LocalDate exitDate, LocalDateTime exitTime) {
this.entryDate = entryDate;
this.entryTime = entryTime;
this.exitDate = exitDate;
this.exitTime = exitTime;
}
//test
// public parkingDetails(LocalDate entryDate, LocalDateTime entryTime, LocalDate exitDate, LocalDateTime exitTime, int user_id ) {
// this.entryDate = entryDate;
// this.entryTime = entryTime;
// this.exitDate = exitDate;
// this.exitTime = exitTime;
// this.parkingUsers.setId(user_id);
// }
//setter gettrs and tostring...

Answer 1

In the ParkingDetails entity, you can have a setter for "parkingUsers" variable to set user object.
In your REST api's saveCarParking() method, before calling "parkingDetailsService.saveParkingUser(d);" you can pass the user object to ParkingDetails using setter created in ParkingDetails.
This should work. No need to explicitly extract the user_id from user's object to pass into ParkingDetails.
Adding one more parameter of type ‘parkingUsers‘ in the constructor of ‘ ParkingDetails’ to initialize user in parking class will also work.
(Apart, it is a good practice to start the class name with a capital letter e.g. instead of having class name as parkingDetails, it should be ParkingDetails.)