Hibernate @OneToMany - 孩子拥有关系，但只有父母 id

Question

I have a @OneToMany relationship defined on the parent class like so:

public class Course {
  @OneToMany(
      mappedBy = "courseId",
      fetch = FetchType.EAGER,
      cascade = CascadeType.ALL,
      orphanRemoval = true)
  private Set<Student> students;
}

On the other side of the relationship, I simply keep the id of the parent entity:

public class Student {
  private Long courseId;
}

When I save a Course with new Students, hibernate first persists the Course, and then tries to persist each Student which is what I would expect. (I can see this via hibernate logging.)

However, when it goes to insert each Student, it is passing a null for the courseId . The database ends up throwing this error: ERROR: null value in column "courseid" violates not-null constraint I have other examples of this working correctly in the code, but for some reason this one is behaving differently.

Is there a reason it's not using the id from the Course it just saved? Is there some other configuration I need to add to support this?

Answer 1

I think you need to change your Student class:

public class Student {

    @ManyToOne
    @JoinColumn(name="course_id", nullable=false)
    private Course course;
}