Question

这真让我感到困惑。

我有以下课程：

Ingredient.java

@Entity
@Table(name = "INGREDIENTS", uniqueConstraints = 
{@UniqueConstraint(columnNames = "NAME")})
public class Ingredient implements Serializable{

@Id
@GeneratedValue
@Column(name = "ingredient_id")
private Long id;

@Column(nullable = false, name = "name")
private String name;

@Column(nullable = false, name = "name")
private Long calories;

public Ingredient() {
}

public Ingredient(String name, Long calories) {
    this.name = name;
    this.calories = calories;
}

public String getName() {
    return name;
}

public void setName(String name) {
    this.name = name;
}

public Long getCalories() {
    return calories;
}

public void setCalories(Long calories) {
    this.calories = calories;
}

public Long getId(){
    return this.id;
}

public void setId(Long id) {
    this.id = id;
}

}

Meal.java

@Entity
@Table(name = "MEALS")
public class Meal implements Serializable {

@ManyToOne
private User user;

@Id
@GeneratedValue
@Column(name = "meal_id")
private Long id;

@ElementCollection(targetClass = Ingredient.class)
private Set<Ingredient> ingredients = new HashSet<>(0);

//More fields and constructors

@ManyToMany(targetEntity = Ingredient.class, cascade = CascadeType.ALL)
@JoinTable(name = "ingredient_meal", joinColumns = {@JoinColumn(name = "meal_id")}, inverseJoinColumns = {@JoinColumn(name = "ingredient_id")})
public List<Ingredient> getIngredients() {
    return ingredients;
}

public void setIngredients(List<Ingredient> ingredients) {
    this.ingredients = ingredients;
}


public Long getId(){
    return this.id;
}

public void setId(Long id) {
    this.id = id;
}

这是我坚持实体的代码：

SessionFactory sessionFactory = 
entityManagerFactory.unwrap(SessionFactory.class);

Session session = sessionFactory.openSession();
session.beginTransaction();

 /***/
Meal coolMeal = new Meal(user, new Date(115, 0, 8), new Time(19, 0, 0), "8 -  
Moules Frites", 1000L);
coolMeal.getIngredients().add(new Ingredient("Fish2", 100L));
        session.persist(coolMeal);
    try{
        session.getTransaction().commit();
    }catch(Throwable e){
        e.printStackTrace();
        throw e;
    }
    session.close();

但我一直得到这个例外：

org.hibernate.TransientObjectException: object references an unsaved transient instance - save the transient instance before flushing: calories.tracker.app.model.Ingredient
at org.hibernate.engine.internal.ForeignKeys.getEntityIdentifierIfNotUnsaved(ForeignKeys.java:294)
at org.hibernate.type.EntityType.getIdentifier(EntityType.java:537)
at org.hibernate.type.ManyToOneType.nullSafeSet(ManyToOneType.java:165)
at org.hibernate.persister.collection.AbstractCollectionPersister.writeElement(AbstractCollectionPersister.java:899)
at org.hibernate.persister.collection.AbstractCollectionPersister.recreate(AbstractCollectionPersister.java:1308)
at org.hibernate.action.internal.CollectionRecreateAction.execute(CollectionRecreateAction.java:67)
at org.hibernate.engine.spi.ActionQueue.executeActions(ActionQueue.java:463)
at org.hibernate.engine.spi.ActionQueue.executeActions(ActionQueue.java:349)
at org.hibernate.event.internal.AbstractFlushingEventListener.performExecutions(AbstractFlushingEventListener.java:350)
at

但是，如果我以这种方式坚持对象：

    Ingredient i1 = new Ingredient("Potatoes2", 100L);
    session.persist(i1);
    Meal coolMeal = new Meal(user, new Date(115, 0, 8), new Time(19, 0, 0), 
    "8 -  Moules Frites", 1000L);
    coolMeal.getIngredients().add(i1);

它工作正常，为什么？一切都与here完全相同。

Answer 1

您为ingredients字段声明了两个映射一个在现场，另一个在吸气器中：

@ElementCollection(targetClass = Ingredient.class)
private Set<Ingredient> ingredients = new HashSet<>(0);    
 ....        
@ManyToMany(targetEntity = Ingredient.class, cascade = CascadeType.ALL)
@JoinTable(name = "ingredient_meal", joinColumns = {@JoinColumn(name = "meal_id")}, inverseJoinColumns = {@JoinColumn(name = "ingredient_id")})
public List<Ingredient> getIngredients() {
    return ingredients;
}

您应该删除该字段的注释：

@ElementCollection(targetClass = Ingredient.class)

@ElementCollection旨在映射非实体类，而Ingredient是实体：

根据Javadoc：

<强> ElementCollection

定义基本类型或可嵌入类的实例集合

Answer 2

您必须使用@OneToMany(mappedBy = "Ord", cascade = CascadeType.ALL, fetch = FetchType.LAZY)，将[{1}}替换为您的实体名称。

无法在Hibernate中保存ManyToMany关系

2 个答案: