How to retrieve data from mapping table using JPQL without JPA Entity class

Question

I have a simple User entity which may have friends (User to User many to many relations) which is mapped in a friends table in database but i don't have a separate Friend entity Object for mapping. Here's the User entity.

@Entity
@Table(name="users")
public class User extends  Persistent{

@NotEmpty
@Size(min=4,max=16)
@Column(name="USER_NAME",nullable = false,unique = true)
private String username;

@NotEmpty
@Email
@Column(name="EMAIL",nullable = false,unique = true)
private String email;

@NotEmpty
@Size(min=3,max=99)
@Column(name="PASSWORD",nullable = false)
private String password;


@Column(name="ACTIVE")
private boolean active = true;

@NotEmpty
@Column(name="FIRST_NAME",nullable = false)
private String firstName;

@NotEmpty
@Column(name="LAST_NAME",nullable = false)
private String lastName;

@NotEmpty
@Column(name="DOB",nullable = false)
private String DOB;

@Column(name="PROFILE_PICTURE")
private String profilePicture;

//user activities

@OneToMany(mappedBy = "user",fetch = FetchType.LAZY,cascade = CascadeType.REMOVE)
private List<Post> posts;

@OneToMany(mappedBy = "user",fetch = FetchType.LAZY,cascade = CascadeType.REMOVE)
private List<Comment> comments;

@OneToMany(mappedBy = "user",fetch = FetchType.LAZY,cascade = CascadeType.REMOVE)
private List<Like> likes;

@ManyToMany(cascade={CascadeType.ALL},fetch=FetchType.EAGER)
@JoinTable(name="friends",
        joinColumns={@JoinColumn(name="userId")},
        inverseJoinColumns={@JoinColumn(name="friendId")})
private List<User> friends;

@ManyToMany(mappedBy="friends",fetch=FetchType.EAGER)
private List<User> friendsWith;
..... 
}

So, I have used eager loading to load friends of User. But say if I want to load friends of User without eagerly loading but using JPQL ... Is it possible to use JPQL to loads User friends info since I don't have a Friend Entity class ?? Do i need to create a separate Friend entity class for mapping freinds ??

Answer 1

You have an association between entities. Associations can be loaded eagerly in JPQL using a fetch join:

select distinct u from User u left join fetch u.friends where u.id = :id

This applies whatever the association is, and whatever the way it's mapped.