你如何映射一个“地图”在冬眠使用注释？ [英] How do you map a "Map" in hibernate using annotations?

问题描述

使用注释如何将字符串中的字段映射到String的Map（Hashtable）到给定对象？这个对象被注解了，它的实例已经存储在hibernate数据库中。

我发现了用简单的键和值定义映射的语法：

$ b

 < class name =Footable =foo> 
 ... 
<地图角色=年龄> 
< key column =id/> 
< index column =nametype =string/> 
< element column =agetype =string/> 
< / map> 
< / class> 
  

奇怪的是一个实体作为键和一个简单类型，就像这样：

 < class name =Footable =foo> 
 ... 
<地图角色=年龄> 
< key column =id/> 
  class =Person/> 
< element column =agetype =string/> 
< / map> 
< / class> 
< class name =Persontable =person> 
 ... 
  type =string/> 
< / class> 
  

但是我不知道如何做到这一点，您可以简单地使用 JPA注释

code> @MapKey （请注意，JPA注释与Hibernate不同，Hibernate @MapKey 映射一个保存地图键的数据库列，while JPA的注解映射了要用作映射关键字的属性）。

pre $ @ javax.persistence.OneToMany（cascade = CascadeType。 ALL）
@ javax.persistence.MapKey（name =name）
private Map< String，Person> nameToPerson = new HashMap< String，Person>（）;


Using annotations how do you map a field in an entity which is a "Map" (Hashtable) of String to a given object? The object is annotated and instances of it are already stored in the hibernate databse.

I've found the syntax for definging a map with a simple key and value as such:

<class name="Foo" table="foo">
    ...
    <map role="ages">
         <key column="id"/>
         <index column="name" type="string"/>
         <element column="age" type="string"/>
     </map>
 </class>

And oddly with an entity as the key and a simple type as the value like so:

<class name="Foo" table="foo">
    ...
  <map role="ages">
    <key column="id"/>
    <index-many-to-many column="person_id" 
         class="Person"/>
    <element column="age" type="string"/>
  </map>
</class>
<class name="Person" table="person">
    ...
    <property name="name" column="name" 
         type="string"/>
</class>

But I don't see how to do this for a simple key to element mapping, and I don't see how to do this using annotations.

解决方案

You could simply use the JPA annotation @MapKey (note that the JPA annotation is different from the Hibernate one, the Hibernate @MapKey maps a database column holding the map key, while the JPA's annotation maps the property to be used as the map's key).

@javax.persistence.OneToMany(cascade = CascadeType.ALL)
@javax.persistence.MapKey(name = "name")
private Map<String, Person> nameToPerson = new HashMap<String, Person>();

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