Removing entity with cascade

Question

Code:

@Entity
class Teacher implements Serializable {
    @Id
    @GeneratedValue(strategy = GenerationType.AUTO)
    Long id;
    @Column(nullable = false)
    @NotNull
    String name;
    @OneToMany(mappedBy = "teacher",cascade = CascadeType.REMOVE)
    List<Course> courses;
}

@Entity
public class Course implements Serializable {
    @Id
    @GeneratedValue(strategy = GenerationType.AUTO)
    Long id;
    @Column(nullable = false)
    @NotNull
    String name;
    @ManyToOne(cascade = CascadeType.REMOVE)
    Teacher teacher;
}

Three questions:

1. Must I put CascadeType.REMOVE in both entities? I want it to work so that if I delete the teacher the course will be deleted automatically.

2. In my database my id doesn't work normally. I want it so that the id increments by one each time, but it currently increases by some random number. Why?

3. I have 2 more @Entity Classes but with @ManyToMany relationship. What must I to do when I want to persist a new object in the database?

Answer 1

1. Probably a duplicate of one of these:
   JPA: Cascade remove does not delete child
   JPA 2.0 orphanRemoval=true VS on delete Cascade
   https://stackoverflow.com/questions/22237631/jpa-does-not-cascade-delete-operation-from-parent-entity-to-child-entity
   Have you checked those references?

2. Need more intel

3. You can persist each of them alone or an instance of Class A with an instance of Classe B attached or vice versa (assuming that you are using the proper CascadeType and @ManyToMany relationship and persistence framework that understands those two)