Problem with relation @ManyToOne in Spring Boot, Hibernate, JPA

Question

I have classes -> Country and City.

I wanna create works request, that when I call to get all countries, I will get all countries, with cities.
When I call to get all cities, I will get all cities with only countries from Country model.
I wanna add new cities with relation to countries.

My Country model class:

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

@NotEmpty(message = "Name of country is mandatory.")
@Column(unique = true)
private String nameOfCountry;

@NotBlank(message = "Name of capital is mandatory.")
private String capital;

@Max(value = 17098242L, message = "Maximum value for population = 10000000000")
private Long surface;

private String countryCode;

private String telephoneCode;

@OneToMany(cascade = CascadeType.PERSIST)
@JoinColumn(name = "country_Id", updatable = false, insertable = false)
private List<CityModelDao> cityModelDao;

My City model class:

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

@NotEmpty(message = "Name of country is mandatory.")
@NotNull
@Column(nullable = false, unique = true)
private String nameOfCity;

I know that I don't have here @ManyToOne, but I still do it wrong and now I haven't got more ideas.

My response from get countries:

And this is it what i want.

But when i call to get cities my response is:

Unfortunately I havent got information about country.

In db I have in cities information about fk from country:

Could you help me to do works relation? I ve tried something like:

CityModel:

    @ManyToOne()
@JoinColumn(name = "country_Id")
private CountryModelDao countryId;

CountryModel:

    @OneToMany(mappedBy = "countryId", orphanRemoval = true, cascade = CascadeType.PERSIST)
private List<CityModelDao> cityModelDao;

But it was wrong. And when I tried with above relation city, I got error.

Could You tell me how to do correct @ManyToOne in this case? What I do wrong?

Thanks

Stoica Raul · Accepted Answer · 2021-03-18 10:46:37Z

2

The most simplistic bi-directional OneToMany relationship model should be:

@OneToMany(mappedBy = "countryId")
private List<CityModelDao> cityModelDao;

You set Country as the owner of the relationship Country - City; You expect an attribute 'countryId' in the CityModelDao;

@ManyToOne
@JoinColumn(name = "country_id")
private CountryModelDao countryId;

You will populate with data based on a join operation that will be executed on the column country_id from the CityModelDao table.

Of course, afterwards, you can enrich the annotations with orphan removal, cascade type etc.

LE: You are using this via REST and you need to avoid the infinite loop.

Please update the relations to:

@JsonManagedReference
@OneToMany(mappedBy = "countryId")
private List<CityModelDao> cityModelDao;

@JsonBackReference
@ManyToOne
@JoinColumn(name = "country_id")
private CountryModelDao countryId;

edited Mar 18, 2021 at 10:46

answered Mar 18, 2021 at 9:00

Stoica Raul

2812 silver badges4 bronze badges

Sign up to request clarification or add additional context in comments.

2 Comments

Patryk Patryk Over a year ago

I add response for your code above, because it was too long to add it in comment.

Stoica Raul Over a year ago

I updated my answer so you can avoid the infinite loop.

Collectives™ on Stack Overflow

Problem with relation @ManyToOne in Spring Boot, Hibernate, JPA

1 Answer 1

2 Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

1 Answer 1

2 Comments

Your Answer

Sign up or log in

Post as a guest

Related