java 如何映射 Map<String,Double>

How to map a Map<String,Double>

提问by Nhaolio

I tried

我试过

@ManyToMany(cascade = CascadeType.ALL)
Map<String, Double> data = new HashMap<String, Double>();

but it produces the error :

但它会产生错误：

   org.hibernate.AnnotationException: Use of @OneToMany or @ManyToMany targeting an unmapped class: com.company.Klass.data[java.lang.Double]
at org.hibernate.cfg.annotations.CollectionBinder.bindManyToManySecondPass(CollectionBinder.java:1016)
at org.hibernate.cfg.annotations.CollectionBinder.bindStarToManySecondPass(CollectionBinder.java:567)
at org.hibernate.cfg.annotations.MapBinder.secondPass(MapBinder.java:80)
at org.hibernate.cfg.CollectionSecondPass.doSecondPass(CollectionSecondPass.java:43)
at org.hibernate.cfg.Configuration.secondPassCompile(Configuration.java:1130)
at org.hibernate.cfg.AnnotationConfiguration.secondPassCompile(AnnotationConfiguration.java:296)
at org.hibernate.cfg.Configuration.buildMappings(Configuration.java:1115)

any idea?

任何的想法？

回答by Pascal Thivent

Well, the error message is pretty clear: Doubleisn't an entity. If you want to map a collection of basic elements, use the CollectionOfElementannotation (from Hibernate) or the ElementCollectionannotation (from JPA 2.0).

好吧，错误消息很清楚：Double不是实体。如果要映射基本元素的集合，请使用CollectionOfElement注释（来自 Hibernate）或ElementCollection注释（来自 JPA 2.0）。

So, assuming you're using Hibernate Annotations 3.4, try this:

因此，假设您使用的是 Hibernate Annotations 3.4，请尝试以下操作：

@CollectionOfElements(targetElement = Double.class)
@org.hibernate.annotations.MapKey(targetElement = String.class)
Map data;

Or, when using generics:

或者，当使用泛型时：

@CollectionOfElements
Map<String, Double> data;

And if you're using Hibernate Annotations 3.5+, prefer the JPA 2.0 annotations:

如果您使用的是 Hibernate Annotations 3.5+，则更喜欢 JPA 2.0 注释：

@ElementCollection(targetClass = Double.class)
@MapKeyClass(String.class)
Map data;

Or, when using generics:

或者，当使用泛型时：

@ElementCollection
Map<String, Double> data;

References

参考

• Hibernate Annotations 3.4 Reference Guide
  • 2.4.6.2.2. Map
  • 2.4.6.2.5. Collection of element or composite elements
• JPA 2.0 specification
  • Section 11.1.12 "ElementCollection Annotation"
  • Section 11.1.28 "MapKeyClass Annotation"

• Hibernate 注释 3.4 参考指南
  • 2.4.6.2.2. 地图
  • 2.4.6.2.5. 元素或复合元素的集合
• JPA 2.0 规范
  • 第 11.1.12 节“ElementCollection 注释”
  • 第 11.1.28 节“MapKeyClass 注释”

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Do you know how to customize the "ELEMENT" and "MAPKEY" column names ?

您知道如何自定义“ELEMENT”和“MAPKEY”列名称吗？

You can fully customize the result. I think the sample below demonstrates everything:

您可以完全自定义结果。我认为下面的示例说明了一切：

@CollectionOfElements(targetElement = Double.class)
@JoinTable(name = "COLLECTION_TABLE", 
    joinColumns = @JoinColumn(name = "PARENT_ID"))
@org.hibernate.annotations.MapKey(targetElement = String.class, 
    columns = @Column(name = "SOME_KEY"))
@Column(name = "SOME_VALUE")
private Map data;

• The name of the collection table for the Mapis defined using the JoinTable
  • The name of the column for the key to the parent is set using a JoinColumnin the JoinTable
• The name of the column for the key of the map is defined in the MapKey
• The name of the column for the value of the map is defined using the Column

• 的集合表的名称Map是使用JoinTable
  • 父项键的列名是使用 a 设置JoinColumn的JoinTable
• 映射键的列名定义在 MapKey
• 映射值的列的名称是使用 Column