从多对多关系中删除 Map 中的 Object

Question

I have an entity Mealplan , where each weekday (enum) contains a meal . This is realised with a map and a Many-to-Many relation like this:

@Entity
public class Mealplan {

  @Id 
  @GeneratedValue(strategy = GenerationType.IDENTITY)
  private int id;

  @ManyToMany
  @SortNatural
  private Map<Weekday, Meal> mealsPerWeek;

(...)

}

This means, in my database the mealsPerWeek property is stored in an extra table. "mealplan_meals_per_week". This table contains the mealplan_id, the meal_per_week_id (mealID) and the weekday_id.

Now, if I remove a Mealplan , everything gets deleted as I am expecting it. But if I want to delete a Meal , following SQL error occurs:

org.h2.jdbc.JdbcSQLIntegrityConstraintViolationException: Referentielle Integrität verletzt: "FKPIBLWWQG1HR2D5W7BGORA9XBB: PUBLIC.ESSENSPLAN_ESSEN_PRO_WOCHE FOREIGN KEY(ESSEN_PRO_WOCHE_ID) REFERENCES PUBLIC.ESSEN(ID) (1)"
Referential integrity constraint violation: "FKPIBLWWQG1HR2D5W7BGORA9XBB: PUBLIC.ESSENSPLAN_ESSEN_PRO_WOCHE FOREIGN KEY(ESSEN_PRO_WOCHE_ID) REFERENCES PUBLIC.ESSEN(ID) (1)"; SQL statement:
delete from essen where id=? [23503-200]

I am expecting that If I delete a Meal, the line in mealplan gets deleted but everything else stays the same.

Note: CasdadeType.REMOVE is not an option, because it deletes every Mealplan too, where the meal i want to remove is in it.

@Entity
public class Essen {

    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    private int id;
    private String name;
}

Answer 1

In mealplan_meals_per_week table there is a reference of Meal in meal_per_week_id column. So where you are trying to delete Meal without cascade reference can't be resolved.

So first delete the references of Meal in mealplan_meals_per_week table and then delete Meal .

Since you are not using Entity for mealplan_meals_per_week , you can use native SQL to define query using nativeQuery.

@Query(
  value = "DELETE FROM mealplan_meals_per_week m WHERE m.meal_per_week_id= ?1", 
  nativeQuery = true)
void deleteByMealId(Interger mealId);