37. Entity 연관관계 - N 대 1

• @ManyToOne
  • @ManyToOne 애너테이션은 N 대 1 관계를 맺어주는 역할을 합니다.
  • 음식 Entity와 고객 Entity가 N 대 1 관계라 가정하여 관계를 맺어보겠습니다.

 

 

단방향

 

 

@Entity
@Table(name = "food")
public class Food {
    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    private Long id;
    private String name;
    private double price;

    @ManyToOne
    @JoinColumn(name = "user_id")
    private User user;
}

@Entity
@Table(name = "users")
public class User {
    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    private Long id;
    private String name;
}

 

 

 

 

 

양방향

 

 

@Entity
@Table(name = "food")
public class Food {
    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    private Long id;
    private String name;
    private double price;

    @ManyToOne
    @JoinColumn(name = "user_id")
    private User user;
}

import java.util.ArrayList;

@Entity
@Table(name = "users")
public class User {
    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    private Long id;
    private String name;

    @OneToMany(mappedBy = "user")
    private List<Food> foodList = new ArrayList<>();
}