java - 使用 OneToMany 映射时 Hibernate 中的连接列为 Null

Question

当使用 onetomany 与 mappedby 映射时，我在 的 uid 列中得到 null车辆表。

一个用户可以拥有许多车辆，因此使用OneToMany映射..

Vehicle 表应包含用户表 ID 的引用 ..

这里，当显示Vehicle表时，我在uid列下得到null。它应该包含用户id<的值。没有mappedby，它工作正常。

    @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]: /image/YyhsN.png

Answer 1

将其添加到您的代码中

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

您没有设置关系的拥有方(车辆->用户)。