休眠manyToMany仅持久

Question

我想在Hibernate中创建一个仅以“ persist”作为级联类型的manyToMany-Relation。

我的用餐课程如下所示：

public class Meal {
    @ManyToMany(cascade = {CascadeType.PERSIST})
    @JoinTable(name="meal_ingredient_relation",
            joinColumns={@JoinColumn(name="meal_id")},
            inverseJoinColumns={@JoinColumn(name="ingredient_id")})
    private Set<Ingredient> ingredients = new HashSet<>();
    ...
}

我的配料课看起来像这样：

public class Ingredient {
    @ManyToMany(mappedBy = "ingredients", cascade = {CascadeType.PERSIST})
    private Set<Meal> meals = new HashSet<>();
    ...
}

如果我想用一些食材做饭

SessionFactory sf = HibernateUtil.getSessionFactory();
Session session = sf.openSession();
session.beginTransaction();

Ingredient ingredient1 = new Ingredient("in1");
Ingredient ingredient2 = new Ingredient("in2");

Meal meal1 = new Meal("meal1", 100);
Meal meal2 = new Meal("meal2", 200);

meal1.getIngredients().add(ingredient1);
meal1.getIngredients().add(ingredient2);
meal2.getIngredients().add(ingredient1);

session.save(meal1);
session.save(meal2);

我收到以下错误：

org.hibernate.TransientObjectException: object references an unsaved transient instance - save the transient instance before flushing: hibernate.entities.Ingredient

Answer 1

您必须在Meal类中为setIngredients添加注释：

@Cascade({CascadeType.SAVE_UPDATE, CascadeType.DELETE})

或者，如果您使用的是XML映射：

<set name="ingredients" cascade="save-update, delete" ...

显然，仅在需要时才使用DELETE 。