How to link many to many not by ID

2 entities House and City and a screenshot of the database. Now I realized that I didn't link it quite correctly, because when a user makes a request, he needs to drive in a number, not a name, of a city, which is not correct. How can I link correctly so that when a request occurs, the name of the city is added to the House and has links with the City?

City

@Data
@Entity
@JsonIgnoreProperties({"hibernateLazyInitializer", "handler"})
@Table(name = "city", schema = "public")
public class City {

@Id
@GeneratedValue(strategy= GenerationType.IDENTITY)
@Column(name = "id")
private Long id;

@OneToMany(cascade = {CascadeType.DETACH, CascadeType.MERGE, CascadeType.PERSIST,
        CascadeType.REFRESH
}, mappedBy = "city")
@ToString.Exclude
@EqualsAndHashCode.Exclude
@JsonIgnore
private Set<House> house;

@Column(name = "id_region", nullable = false)
private Integer id_region;
@Column(name = "name", nullable = false)
private String name;
}

House

@Data
@Entity
@JsonIgnoreProperties({"hibernateLazyInitializer", "handler"})
@Table (name = "house", schema = "public")
public class House {

    @Id
    @GeneratedValue(strategy=GenerationType.IDENTITY)
    @Column(name = "id")
    private Long id;

    @ManyToOne(fetch = FetchType.LAZY)
    @JoinColumn(name = "city_id")
    private City city;

    @OneToMany(mappedBy = "house")
    private Set<Contract> contract;

    @Column(name = "id_landlord", nullable = false)
    private Long id_landlord;
    @Column(name = "outside", nullable = false)
    private String outside;
    @Column(name = "rooms", nullable = false)
    private Integer rooms;
    @Column(name = "price", nullable = false)
    private Double price;
    @Column(name = "description", nullable = false)
    private String description;
    @Enumerated(value = EnumType.STRING)
    @Column(name = "status")
    private Status status;
}

You need to link entities in the database (with rare exceptions) by id. Where the id comes from in the code that, say, creates House is another question, and now we will consider it.

Indeed, usually the user does not enter an id, as this is inconvenient. But specifying the name of the city in the text box is also not user-friendly, and they don't do that. For example, what happens if a user makes a typo?

It is important that the user does not specify an arbitrary city. If a link to a city is stored in the House (directly or through an intermediate table - it doesn't matter), then the user chooses from the existing cities.

In practice, this means that the system gives the user a choice of a city. It can be either a drop-down list, or an incremental search with confirmation of the selection, or a search by criteria, again, with confirmation of the selection. The important thing here is that in the UI the user sees the exact name of the city, then that this city, in principle, is available for selection. At the very same choice, the program uses the id of the selected city to create a House.

Therefore, the specific implementation depends on what you use in the UI. In a database, service and even MVC controller, you need to use id.