@ManyToMany 关系，JPA

Question

I have an issue here, I am trying to make FoodProgram with two entities: FoodProgram-holds 4 meals with List for each meal. And FoodEntity with name, calories and id. The idea is that each meal can choose from all foods, and foods can repeat in every meal(if we eat eggs for lunch, we can add them to dinner too). I have @ManyToMany annotation in my FoodProgram class. Problem is there, when I try to getLunch from FoodProgram, I got error for lazily initialize, but I cannot put fetchtype.EAGER on every annotation, because I get another error. Should I just make another entity and to figure out different approach?

FoodEntity

@Entity
public class Food {
@Id
@GeneratedValue(strategy = GenerationType.IDENTITY)
private Long id;
private String name;
private Integer calories;

public Food() {
}

FoodProgram entity

@Entity
public class FoodProgram {
@Id
@GeneratedValue(strategy = GenerationType.IDENTITY)
private Long id;
@ManyToMany
private List<Food> breakfast;
@ManyToMany
private List<Food> lunch;
@ManyToMany
private List<Food> afterLunch;
@ManyToMany
private List<Food> dinner;

public FoodProgram() {
}

Answer 1

With a pure sql model point of view, what's the difference between breakfast, lunch, afterLunch and dinner ?

You have two solutions :

1. you need to implement sql inheritance through your hibernate model first. Have a look at here https://www.baeldung.com/hibernate-inheritance .

2. you have to specify the dedicated @JoinTable for each relationship

In other words, your implementation definitely cannot work like this.