@Entity
public class User {
    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    private Long id;

    @OneToOne
    @JoinColumn(name = "profile_id", referencedColumnName = "id")
    private Profile profile;
}

@Entity
public class Profile {
    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    private Long id;

    private String bio;
}
Здесь связь между User и Profile устанавливается через внешний ключ profile_id.

@Entity
public class Student {
    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    private Long id;

    @ManyToMany
    @JoinTable(
        name = "student_course",
        joinColumns = @JoinColumn(name = "student_id"),
        inverseJoinColumns = @JoinColumn(name = "course_id")
    )
    private List<Course> courses;
}

@Entity
public class Course {
    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    private Long id;

    private String title;

    @ManyToMany(mappedBy = "courses")
    private List<Student> students;
}
Связь осуществляется через промежуточную таблицу student_course.

@Entity
public class Order {
    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    private Long id;

    @ManyToOne
    @JoinColumn(name = "customer_id", nullable = false)
    private Customer customer;
}
Здесь customer_id в таблице Order будет внешним ключом, ссылающимся на таблицу Customer.

@Entity
public class Document {
    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    private Long id;

    @Lob
    private String content; // Для больших текстов

    @Lob
    private byte[] fileData; // Для бинарных данных
}

public interface UserRepository extends JpaRepository<User, Long> {

    @Query("SELECT u FROM User u WHERE u.email = :email")
    User findByEmail(@Param("email") String email);
}

public interface UserRepository extends JpaRepository<User, Long> {

    @Modifying
    @Query("UPDATE User u SET u.name = :name WHERE u.id = :id")
    void updateUserName(@Param("id") Long id, @Param("name") String name);
}

@Configuration
@EnableJpaRepositories(basePackages = "com.example.repository")
public class AppConfig {
}

@ManyToOne
@JoinColumn(name = "user_id", referencedColumnName = "id", nullable = false)
private User user;