@OneToMany and @ManyToOne Jpa

Question

In my spring JPA project I have two entities, Task and Developer. List can assign to a Developer and one Task can have just one Developer. I mapped them:

Developer

@Entity
@Table(name = "DEVELOPER")
public class Developer implements Serializable {
    @Id
    @GeneratedValue(strategy = GenerationType.AUTO)
    private Long id;
    private String name;

    @OneToMany(targetEntity = Task.class , mappedBy = "developer",cascade=CascadeType.ALL, fetch = FetchType.LAZY)
    private List<Task> taskList;

Task

@Entity
@Table(name = "TASK")
public class Task implements Serializable {

    @Id
    @GeneratedValue(strategy = GenerationType.AUTO)
    private Long taskId;
    private String taskTitle;

    @ManyToOne
    @JoinColumn(name="developer_id")
    private Developer developer;

When I assign a List of Task to a Developer, JSON format is:

{
    "id": 1,
    "name": "John",
    "taskList": [
        {
            "taskId":2,
            "taskTitle": "Do sth"
        }
        ]
}

But the value of Developer in above Task object is null:

{
  "taskId":2,
   "taskTitle": "Do sth",
   "developer": null
}

I expect to this developer property is not null and Developer and task have a bidirectional relationship. How can I solve this? I am new in Spring and Hibernate. Any help would be greatly appreciated.

Answer 1

might missing cascade=CascadeType.ALL in @ManyToOne annotation, and in Java doc, it says: (Optional) The operations that must be cascaded to the target of the association.By default no operations are cascaded. ， https://docs.jboss.org/hibernate/jpa/2.1/api/javax/persistence/ManyToOne.html

Answer 2

Remove cascade=CascadeType.ALL in Developer class and add @joinColumn annotation, it will work.

Developer class will look like this-

@Entity
@Table(name = "DEVELOPER")
public class Developer implements Serializable {
@Id
@GeneratedValue(strategy = GenerationType.AUTO)
private Long id;
private String name;

@OneToMany(targetEntity = Task.class , mappedBy = "developer", fetch = FetchType.LAZY)
@JoinColumn(name="task_developer_id")
private List<Task> taskList;