如何 map 集合 Map <string,list<string> &gt; 使用 Hibernate 键入</string,list<string>

Question

问题是使用 Hibernate 坚持以下 class。

Public class Album{
Private int albumid;
Private String aname;
Private Map<String,List<String>> photos;
}

我试过这个

@Entity
public class Album {
    @Id
    private int albumId;
    @Column(name= "Album_Name")
    private String aname;
    
    @ElementCollection
    @MapKeyColumn(name= "Event_Name")
    @Column(name="Values")
    private Map<String, List<String>> photos;

但它显示错误，例如

    Exception in thread "main" org.hibernate.MappingException: Could not determine type for: java.util.List, at table: Album_photos, for columns: [org.hibernate.mapping.Column(Values)]
        at org.hibernate.mapping.SimpleValue.getType(SimpleValue.java:336)
        at org.hibernate.mapping.SimpleValue.isValid(SimpleValue.java:310)
        at org.hibernate.mapping.Collection.validate(Collection.java:315)
        at org.hibernate.mapping.IndexedCollection.validate(IndexedCollection.java:89)
        at org.hibernate.cfg.Configuration.validate(Configuration.java:1362)
        at org.hibernate.cfg.Configuration.buildSessionFactory(Configuration.java:1849)
        at org.hibernate.cfg.Configuration.buildSessionFactory(Configuration.java:1928)
        at com.wipro.Insert.main(Insert.java:17)

Answer 1

此映射不适用于 Hibernate ORM。

The reason is that you are trying to have two nested collections of elements and this is not supported by Hibernate ORM (first collection is the Map and the second collection is the the List ).

你必须使用实体。

您可以通过以下映射获得类似于@ElementCollection的内容：

@Entity
public static class PhotoEvent {
    @Id
    @Column(name = "Event_Name")
    public String eventName;

    @ElementCollection
    @Column(name = "`Values`")
    public List<String> values;

    @ManyToOne
    public Album album;
...
// getter/setter/hascode/equals...
}


@Entity
public static class Album {
    ...
    
    @OneToMany(mappedBy = "album", fetch = FetchType.EAGER, cascade = CascadeType.ALL, orphanRemoval = true)
    @MapKey(name = "eventName")
    public Map<String, PhotoEvent> photoEvents;
    
    ...
}

请注意，我设置FetchType.EAGER是因为它模拟了@ElementCollection ，但您可能希望将其设置为LAZY （默认值）。

您将在 Hibernate ORM 文档中找到有关此类映射的更多详细信息。