ManyToOne gives null on two tables on create spring boot hiernate jpa

For example if have table "user" and "address" and a user can have 1 to more addresses, so the relation is one to many. When I insert data I will insert inside the same json the user and the address list.

The problem is that on create the field that related these two is null. I can't find the right way how to insert data so it will create all of these and then populate also the field where onetomany relation is done.

I have two tables which are related to each other, table "user" and "address":

@Entity
@Table(name = "user")
@Data
public class User{

    @Id
    @GeneratedValue(strategy = GenerationType.AUTO)
    private Integer id;

    @NotNull
    @Column(unique = true)
    private String user_name;

    @Column
    private String description;

    @OneToMany(mappedBy = "user", cascade = CascadeType.ALL, orphanRemoval = true)
    protected Set<Address> addresses= new HashSet<>();
}

While in the other table:

@Entity
@Table(name = "address")
@Data
public class Address{

    @Id
    @GeneratedValue(strategy = GenerationType.AUTO)
    private Integer id;

    @ManyToOne
    @JoinColumn(name = "user_id")
    protected User user;

    private String description;
}

I did a post request to create new user with some addresses:

@PostMapping ("/user/create")
public ResponseEntity post(@RequestBody User user) {
    jpaRepository.save(user);
     // return
}

In a post request I sent this json:

{
 
  "user_name": "example",
  "description": "this is a  user description",
  "comments": [
    {
      "description": "this is a address 1"
    },
    {
      "description": "this is a address 2"
    }
  ]
}

When I insert data I get the "address" table the "user_id" is null, the data are inserted but the relations are not there?
What I'm doing wrong here? Please help!

Update:
I thought on doing something like this but don't know how to call it:

public class User{
    
    ....
    
     public void addAddress(Address address) {
        address.setUser(this);
        addresses.add(address);
    }

}

It doesn't work like that,

Basically you have another DB table for adresses and that means that these addresses have to be saved in the Database, so that they can have an identifier and user_id.

I would recommend creating another Repository for addresses.
And whenever you need to add an Address to a User
Do something like this:

@PostMapping("/user/{id}/addAddress")
public Address addAddressToUser(@RequestBody Address newAddress, @PathVariable(name="id") int userId)
{
    User selectedUser = userRepo.findById(userId).orElseThrow( /* throw your exception */);
    newAddress.setUser( selectedUser );

    return addressRepo.save( newAddress )
}

And basically you have to make a call like this:

POST http://localhost:8080/user/1/addAddress

And in the Request body a Json :

{
    "description" : "This is a new Address"
}

UPDATE:
As requested by the asker, this is a way to perform this in one call with User and Addresses inside.
Code was not compiled, but logic is clear.

@PostMapping("/addUser)
public User addUser(@RequestBody User newUser)
{
    List<Address> addresses = newUser.getAddresses(); // We take all the addresses that are in the call
        
    newUser.setAddresses(new List<Address>()) // We empty the addresses in this User
        
    //Now for each address that was in the call, we save it the DB add it to user    
    addresses.forEach( address ->
    {
        address = addressRepo.save(address) // saves each address in the DB
        
        newUser.getAddresses().add(address); // add this Address to this user (SINCE NOW IT HAS AN ID IN THE DB)
    });
    
    //After everything is finished save this user to the Db with the Addresses and return it
    return userRepo.save(newUser);    
    
    
}

You need to use it for join column(user) => @JoinColumn(name = "users_id",nullable = false)