[FIXED] Hibernate Unidirectional OneToMany Relationship with Not-null Constraint in Foreign Key

Issue

I have two tables like this

at first, i try to set course_id foreign key in review table to have not null constraint for the sake of data integrity.

So i create annotated class like for these two table like below:

@Data
@Entity
@Table(name = "course")
public class Course {
    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    @Column(name = "course_id")
    private int id;

    @Column(name = "name")
    private String name;

    @OneToMany(fetch = FetchType.LAZY,cascade = CascadeType.ALL)
    @JoinColumn(name = "course_id")
    private List<Review> reviews;

    public Course(){}

    public Course(String name){
        this.name = name;
    }

    public void addReview(Review review){
        if(this.reviews == null){
            this.reviews = new ArrayList<>();
        }
        this.reviews.add(review);
    }
}

@Data
@Entity
@Table(name = "review")
public class Review {
    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    @Column(name = "review_id")
    private int reviewId;

    @Column(name = "rating")
    private int rating;

    public Review(){}

    public Review(int rating){
        this.rating = rating;
    }
}

and i create simple app to add review to an exsiting course like code below:

session.beginTransaction();

// get instructor from db
Course course = session.get(Course.class, 3);

// create review
Review review1 = new Review(4);

course.addReview(review1);

// save to db
session.save(course);

session.getTransaction().commit();

but this program will throw an error because it violates not null constraint i set in database before

Caused by: org.postgresql.util.PSQLException: ERROR: null value in column "course_id" violates not-null constraint

but if remove the not null constraint this program works fine because hibernate will execute insert with null value first than update the value like below:

Hibernate: insert into review (rating) values (?)
Hibernate: update review set course_id=? where review_id=?

is there a way for hibernate to insert directly with course_id value so i can keep the not null constraint?

Thanks!

Solution

You need to specify in the mapping that the column is not nullable:

@JoinColumn(name = "course_id", nullable = false)

Answered By - Davide D'Alto
Answer Checked By - Gilberto Lyons (JavaFixing Admin)