How do I autojoin my users table with roles table

My users table is as following:

emp_user table
--------------
id (bigint) PK
uuid (character varying) unique
username (character varying) unique
-- no foreign keys are defined in the table

The UserEntity class is as following:

@Entity
@Table(name = "emp_user")
public class UserEntity {
    @Id
    private String uuid; // Because of Keycloak internals
    
    @Column(name = "\"user\"")
    private String username;
    
    @Column(name = "id")
    private Long identifier;
    
    @OneToMany
    JoinColumn(referencedColumnName = "emp_user_id")
    private List<Roles> rolesList;
    
    // getters and setters
}

A user can has many roles.

emp_user_roles table
--------------------
emp_user_id (bigint)
emp_user_role (character varying)
-- both emp_user_id and emp_user_role together is a key
-- no foreign keys are defined in the table

The Roles class is as following:

@Entity
@Table(name = "emp_user_roles")
public class Roles implements Serializable {
    @Id
    @Column(name = "emp_user_id")
    private Long userId;
    
    @Id
    @Column(name = "emp_user_role")
    private String userRole;
    
    // getters and setters
}

I get a result, one user, with rolesList but inside of it there are no roles but only an error message saying Unable to evaluate the expression Method threw 'org.hibernate.exception.GenericJDBCException' exception.

I think I'm doing something wrong.

You have to use many-to-many association because a Role can have multiple users. Hibernate will create a join table in such case.

@Entity
public class User {

    @Id
    @GeneratedValue
    private Long id;

    @ManyToMany(fetch = FetchType.LAZY)
    private List<Role> roles;

}

@Entity
public class Role {

    @Id
    private Long id;

    @Column
    private String name;

}

You can create an additional entity UserRoleMapping with @ManyToOne to User and @ManyToOne to Role. It will be simply to add or delete Role. You will not need to get all roles list to remove one of them. Also you can add unique constraint (User, Role) to the UserRoleMapping.

Here is how I have solved the issue:

@Entity
@Table(name = "emp_user")
public class UserEntity implements Serializable { // <-- must implement Serializable
    @Id
    private String uuid;

    @Column(name = "\"user\"")
    private String username;

    @Column(name = "id")
    private Long identifier;

    @OneToMany
    @JoinColumn(name = "emp_user_id", referencedColumnName = "id") // <-- both name and referencedColumnName are required
    private List<Roles> rolesList;

    // getters and setters
}