POST request with Many-to-many relationship in Spring Data REST - spring

Question

I'm trying to add a movie to MySQL database, here's my database schema:
Movie(id, name)
Genre(id, name)
Movie_genre(id_movie, id_genre)
And here's my model classes:
Movie.ts
public class Movie {
private Short id;
private String name;
private List<MovieGenre> movieGenres;
#Id
#GeneratedValue(strategy = GenerationType.IDENTITY)
#Column(name = "id", nullable = false)
public Short getId() {
return id;
}
public void setId(Short id) {
this.id = id;
}
#Column(name = "name", nullable = false, length = 100)
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
#OneToMany(mappedBy = "movie")
public List<MovieGenre> getMovieGenres() {
return movieGenres;
}
public void setMovieGenres(List<MovieGenre> movieGenres) {
this.movieGenres = movieGenres;
}
}
Genre.ts
public class Genre {
private Short id;
private String name;
private List<MovieGenre> movieGenres;
#Id
#GeneratedValue(strategy = GenerationType.IDENTITY)
#Column(name = "id", nullable = false)
public Short getId() {
return id;
}
public void setId(Short id) {
this.id = id;
}
#Column(name = "name", nullable = false, length = 15)
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
#OneToMany(mappedBy = "genre")
#JsonIgnore
public List<MovieGenre> getMovieGenres() {
return movieGenres;
}
public void setMovieGenres(List<MovieGenre> movieGenres) {
this.movieGenres = movieGenres;
}
}
MovieGenre.ts ( that model stands for the generated table )
public class MovieGenre {
private MovieGenrePK id;
private Movie movie;
private Genre genre;
#EmbeddedId
#JsonIgnore
public MovieGenrePK getId() {
return id;
}
public void setId(MovieGenrePK id) {
this.id = id;
}
#MapsId("movieId")
#ManyToOne
#JoinColumn(name = "movie_id", referencedColumnName = "id", nullable = false)
#JsonIgnore
public Movie getMovie() {
return movie;
}
public void setMovie(Movie movie) {
this.movie = movie;
}
#MapsId("genreId")
#ManyToOne
#JoinColumn(name = "genre_id", referencedColumnName = "id", nullable = false)
public Genre getGenre() {
return genre;
}
public void setGenre(Genre genre) {
this.genre = genre;
}
}
and because we have composite key in the last model, we need a class for that :
public class MovieGenrePK implements Serializable {
private Short movieId;
private Short genreId;
#Column(name = "movie_id", nullable = false)
public Short getMovieId() {
return movieId;
}
public void setMovieId(Short movieId) {
this.movieId = movieId;
}
#Column(name = "genre_id", nullable = false)
public Short getGenreId() {
return genreId;
}
public void setGenreId(Short genreId) {
this.genreId = genreId;
}
}
So I'm trying to add a movie with genres by making a post request, first i made a post request for adding a movie and another one for adding a genre, that's works fine, now i need to associate a genre to a movie.
I tried the following:
I made a POST request to the following endpoint: http://localhost:8080/api/movieGenres with application/json header and with the following body:
{
"movie": "http://localhost:8080/api/movies/6",
"genre": "http://localhost:8080/api/genres/1"
}
but i got the error:
{
"timestamp": "2018-08-22T21:10:30.830+0000",
"status": 500,
"error": "Internal Server Error",
"message": "NullPointerException occurred while calling setter of com.movies.mmdbapi.model.MovieGenrePK.genreId; nested exception is org.hibernate.PropertyAccessException: NullPointerException occurred while calling setter of com.movies.mmdbapi.model.MovieGenrePK.genreId",
"path": "/api/movieGenres"
}

Answer 1

You have to instatiate MovieGenrePK, change:
public class MovieGenre {
private MovieGenrePK id;
}
to
public class MovieGenre {
private MovieGenrePK id = new MovieGenrePK();
}