多對多關系：org.hibernate.MappingException：無法確定以下類型：java.util.Set

Question

我正在嘗試根據此示例與JPA建立多對多雙向關系： http : //www.mkyong.com/hibernate/hibernate-many-to-many-example-join-table-extra-column-注解/

我得到一個

org.hibernate.MappingException：無法確定類型：java.util.Set，在表：T_ITEM，用於列：[org.hibernate.mapping.Column（itemHikes）]

如果有人可以幫助我，請參見以下源代碼：

類項目

@Entity
@Table(name="T_ITEM")
public class Item implements Serializable {
    private static final long serialVersionUID = 1L;

    @Id
    private Long id;
    private Set<ItemHike> itemHikes = new HashSet<ItemHike>(0);

    @OneToMany(fetch = FetchType.LAZY, mappedBy = "pk.item", cascade=CascadeType.ALL)
    public Set<ItemHike> getItemHikes() {
        return this.itemHikes;
    }

    public void setItemHikes(Set<ItemHike> itemHikes) {
        this.itemHikes = itemHikes;
    }
}

班級遠足

@Entity
@Table(name="T_HIKE")
public class Hike implements Serializable {
    private static final long serialVersionUID = 1L;

    @Id
    private Long id;

    private List<ItemHike> itemHikes = new ArrayList<ItemHike>(0);

    @OneToMany(fetch = FetchType.LAZY, mappedBy = "pk.hike", cascade=CascadeType.ALL)
    public List<ItemHike> getItemHikes() {
        return this.itemHikes;
    }

    public void setItemHikes(List<ItemHike> itemHikes) {
        this.itemHikes = itemHikes;
    }
}

類項目遠足

@Entity
@Table(name="T_ITEM_HIKE")
@AssociationOverrides({
    @AssociationOverride(name = "pk.item", 
        joinColumns = @JoinColumn(name = "iditem")),
    @AssociationOverride(name = "pk.hike", 
        joinColumns = @JoinColumn(name = "idlist")) })


public class ItemHike implements Serializable {
    private static final long serialVersionUID = 1L;

    @EmbeddedId
    private ItemHikePK pk;

    private int quantity;

    //bi-directional many-to-one association to THike

    @Transient
    public Item getItem() {
        return getPk().getItem();
    }

    public void setItem(Item item) {
        getPk().setItem(item);
    }


    @Transient
    public Hike getHike() {
        return getPk().getHike();
    }

    public void setHike(Hike hike) {
        getPk().setHike(hike);
    }

    public ItemHike() {
    }

    public ItemHikePK getPk() {
        return this.pk;
    }

    public void setPk(ItemHikePK pk) {
        this.pk = pk;
    }

    public int getQuantity() {
        return this.quantity;
    }

    public void setQuantity(int quantity) {
        this.quantity = quantity;
    }
}

類別項目

@Embeddable
public class ItemHikePK implements Serializable {
    //default serial version id, required for serializable classes.
    private static final long serialVersionUID = 1L;

    private Item item;
    private Hike hike;

    @ManyToOne
    public Item getItem() {
        return item;
    }

    public void setItem(Item item) {
        this.item = item;
    }

    @ManyToOne
    public Hike getHike() {
        return hike;
    }

    public void setHike(Hike hike) {
        this.hike = hike;
    }
}

Answer 1

這是一個類似的問題！

您要在Fields上以及Getters上設置@Anottations，這是錯誤的，您必須在Fields或Getters方法上放置注釋。

錯誤的方法：

@Entity
@Table(name="T_ITEM")
public class Item implements Serializable {
    private static final long serialVersionUID = 1L;

    @Id
    private Long id;
    private Set<ItemHike> itemHikes = new HashSet<ItemHike>(0);

    @OneToMany(fetch = FetchType.LAZY, mappedBy = "pk.item", cascade=CascadeType.ALL)
    public Set<ItemHike> getItemHikes() {
        return this.itemHikes;
    }

    public void setItemHikes(Set<ItemHike> itemHikes) {
        this.itemHikes = itemHikes;
    }
}

正確：

@Entity
@Table(name="T_ITEM")
public class Item implements Serializable {
    private static final long serialVersionUID = 1L;

    @Id
    private Long id;
    @OneToMany(fetch = FetchType.LAZY, mappedBy = "pk.item", cascade=CascadeType.ALL)
    private Set<ItemHike> itemHikes = new HashSet<ItemHike>(0);

    public Set<ItemHike> getItemHikes() {
        return this.itemHikes;
    }

    public void setItemHikes(Set<ItemHike> itemHikes) {
        this.itemHikes = itemHikes;
    }
}

Answer 2

嘗試將@OneToMany注釋從getItemHikes()移至itemHikes字段。 如果您希望注釋有時出現在字段中，有時出現在getter上，則需要使用@Access注釋。 如果您不使用它，則所有注釋都必須在字段上或在吸氣劑上，但不能同時使用。