mapping a entity which have two refer to another s

问题:

I have two entity,one of them(the Task) own two refers of another entity(The user).

public class Task{
    private int id;

    private User publisher;

    private List<User> manager;
}

public User{
    private int id;
    private String name;
    private List<Task> tasks;
}

At the Task side,I can set "one-to-one" to "publisher",and "one-to-many" to "manager",but how to set the mapping in the user side?

回答1:

It depends on what you want to have in the database.

If you want to have a separate foreign key for publisher and join table for manager, the easiest way to map the other side it this:

public class Task{
    @ManyToOne 
    private User publisher;

    @ManyToMany
    private List<User> manager;

     ...
}

public User{
     @OneToMany(mappedBy = "publisher")
     private List<Task> publishedTasks;

     @ManyToMany(mappedBy = "manager")
     private List<Task> managedTasks;

     ...
}

If you actaully need a single list of tasks in User, you can create it programmatically.

Alternatively, you can have a single join table with an additional Role property:

public enum Role { PUBLISHER, MANAGER }

public class Task{
    @ManyToMany
    @MapKeyEnumerated
    private Map<Role, User> participants;
     ...
}

public User{
    @ManyToMany(mappedBy = "participants")
    private List<Task> tasks;
     ...
}

Also think whether you need this relationship to be bidirectional at all. It looks like there are not so many use cases when you need a list of all tasks where a particular user participate. Perhaps you don't need this relationship at the User side at all, and can use queries instead.