使用OneToMany映射时在Hibernate的Join列中获取Null

Question

When using onetomany mapping with mappedby I'm getting null in column of uid of vehicle table.

One User can have many vehicle s so OneToMany mapping used ..

Vehicle table should contain reference of user table id ..

Here I'm getting null under uid column when Vehicle table is displayed .It should contain value of user id . Without mappedby , it is working fine.

    @Entity
            @Table(name="User_Details")
            public class UserDetails {                               
                private long uid;
                @Column(name="fname")
                private String name;
                private Set<Vehicle> vehicle=new HashSet<Vehicle>();
                public UserDetails() {

                }
                public UserDetails(String name) {

                    this.name = name;

                }

                @Id
                @Column(name="uid")
                @GeneratedValue
                public long getUid() {
                    return uid;
                }
                public void setUid(long uid) {
                    this.uid = uid;
                }
                public String getName() {
                    return name;
                }
                public void setName(String name) {
                    this.name = name;
                }


                @OneToMany(mappedBy="user",cascade = CascadeType.ALL)
                public Set<Vehicle> getVehicle() {
                    return vehicle;
                }
                public void setVehicle(Set<Vehicle> vehicle) {
                    this.vehicle = vehicle;
                }
                }

        @Entity
        @Table(name="Vehicle")
        public class Vehicle {

            private long id;
            @Column(name="vname")
            private String name;
            private UserDetails user;
            public Vehicle() {

            }
            public Vehicle(String name, UserDetails user) {
                super();
                this.name = name;
                this.user = user;
            }

            @Id
            @Column(name="vid")
            @GeneratedValue
            public long getId() {
                return id;
            }
            public void setId(long id) {
                this.id = id;
            }
            public String getName() {
                return name;
            }
            public void setName(String name) {
                this.name = name;
            }
            @ManyToOne
            @JoinColumn(name = "uid")   **References UserDetails table**
            public UserDetails getUser() {
                return user;
            }
            public void setUser(UserDetails user) {
                this.user = user;
            }

        }
    public class App {


        public static void main(String\[\] args) {

            SessionFactory sessionFactory=new Configuration().configure().buildSessionFactory();
            Session session=sessionFactory.openSession();
            session.beginTransaction();

            UserDetails user=new UserDetails();
            user.setName("Rohit");


            Vehicle vehicle1=new Vehicle();
            vehicle1.setName("Hyundai1");
            Vehicle vehicle2=new Vehicle();
            vehicle2.setName("Maruti1");

            Set<Vehicle> set = new HashSet<Vehicle>();
            set.add(vehicle1);
            set.add(vehicle2);
            user.setVehicle(set);

            session.save(user);

            session.getTransaction().commit();
            session.close();

        }**][1]][1]




  [1]: https://i.stack.imgur.com/YyhsN.png

Answer 1

Add this to your code

vehicle1.setUser(user)
vehicle2.setUser(user)

You don't set the owning side (vehicle->user) of the relationship.