Values are not saved in the database

Why do I have null id_house and id_tenant if I send values? The date is saved correctly. How do I set the tenant for an apartment and which apartment is being rented?

I accept values:

@PostMapping("/rent")
    @PreAuthorize("hasAuthority('user:write')")
    public void homeRent(@RequestBody Contract contract) {
        contractRepository.save(contract);
    }

Contract:

@Data
@Entity
@Table(name = "contract", schema = "public")
public class Contract {
    @Id
    @GeneratedValue(strategy= GenerationType.IDENTITY)
    @Column(name = "id")
    private Long id;

@ManyToOne
@JoinColumn(name = "id_house")
@ToString.Exclude
@EqualsAndHashCode.Exclude
@JsonIgnore
private House house;

@ManyToOne
@JoinColumn(name = "id_tenant")
@EqualsAndHashCode.Exclude
@ToString.Exclude
@JsonIgnore
private User user;

@Column(name = "end_date")
private LocalDate end_date;
@Column(name = "start_date")
private LocalDate start_date;
}

Postman:

{
    "start_date" : "2020-03-12",
    "end_date" : "2020-03-19",
    "id_house" : 2,
    "id_tenant" : 3
}

First what I see wrong is why do you have id_tenant in your JSON request when it is actually user? Keep in mind id_tenant is just column name, not field name.

Also you should provide object {} not integer for user so your request would look something like

{
...
  "user": {"id": 1....}
...
}

@PostMapping("/rent")
    @PreAuthorize("hasAuthority('user:write')")
    public void homeRent(@RequestBody ContractDto contractDto) {
        Contract contract = new Contract();
        House house = houseRepository.findById(contractDto.getId_house()).orElseThrow();
        User user = userRepository.findById(contractDto.getId_tenant()).orElseThrow();
        contract.setHouse(house);
        contract.setUser(user);
        contract.setStart_date(contractDto.getStart_date());
        contract.setEnd_date(contractDto.getEnd_date());

        contractRepository.save(contract);
    }