对未知实体的引用：java.lang.Integer

Question

I'm having simple @Entity class

@Entity
@Table(name = "user")
@Getter       
class User {
    @Id
    @GeneratedValue
    private final Integer userID;    
    private final String username;   
}

And another one, that should hold foreign key to it

@Getter
@Builder
@Entity
class Task {
    @Id
    @GeneratedValue
    private final Integer taskID;

    private final String title;
    private final String details;

    @ManyToOne(cascade = CascadeType.PERSIST)
    @JoinTable(name = "user", joinColumns = {@JoinColumn(name = "userID")})
    private final Integer userID;
}

The point is - User and Task classes are in separated packages and both are package scoped. Means I can't simply write

@ManyToOne(cascade = CascadeType.PERSIST)
@JoinTable(name = "user", joinColumns = {@JoinColumn(name = "userID")})
private final User user;

And thats why I'm getting

@OneToOne or @ManyToOne on com.johndoe.teamplanner.task.domain.Task.userID references an unknown entity: java.lang.Integer

Is there a workaround, to achieve what I need? Create relationship between 2 entities that are in separated packages and with package scope?

Answer 1

You could try the following alternatives:

• The obvious one: change the accessor of the class User to public . But, if you asked this is probably because you couldn't change it because you don't have the source code.
• Decompile the User .class file in order to get the source. If User isn't so complex, you probably could try this. Then, change the accessor to public .
• Generate your own version of the User class and use yours for persistence and the other one for the functionalities it provides.
• Map the userID in Task class just as an Integer and assure by code that you never assign a value that isn't a valid userID: @Column private Integer userID; . If you are using JPA to generate the tables, then you need to add manually the foreign key in the database to assure the integrity of your data.

I hope some of these solutions could help.