JPA @OneToMany和@ManyToOne:后引用为空

@Entity
public class User {
    @Id
    @GeneratedValue
    private Long id;

    private String name;

    @OneToMany(mappedBy = "user")
    private List<Address> addresses;

    // ... getters and setters
}

@Entity
public class Address {
    @Id
    @GeneratedValue
    private Long id;

    private String street;

    @ManyToOne
    private User user;

    // ... getters and setters
}

@Entity
public class User {
    @Id
    @GeneratedValue
    private Long id;

    private String name;

    @OneToMany(mappedBy = "user")
    private List<Role> roles;

    // ... getters and setters
}

@Entity
public class Role {
    @Id
    @GeneratedValue
    private Long id;

    private String name;

    @ManyToOne
    private User user;

    // ... getters and setters
}