映射来自第三方库的值对象 [英] Mapping value objects from third party libraries

问题描述

我有以下需要通过Hibernate 注解持久化到关系数据库的实体：

  @Entity 
 @Table（name =fizzes）
 public class Fizz {
 @Id @GeneratedValue 
 @Column（name =fizz_id）
 private int id; 
 
 @Column（name =fizz_wooz）
 private String wooz; 
 
 // ???这里我不确定！ 
私人Buzz嗡嗡声; 
 
 //构造函数，getters / setters在这里等等... 
} 
 
 public class Buzz {
 private int jupiter; 
 
私人字符串海王星; 
 
 //构造函数，getters / setters在这里，等等... 
} 
  

Buzz 的问题是：

• strong> not 希望它成为它自己的实体/表。我希望它是一个值对象/类型，它被映射到 fizzes 表（通过向其添加列）
  
• Buzz 来自第三方库，因此我无法修改它

因此，我要找的表格的最终结果是：

  [fizzes] table 
 ============== 
 fizz_id，PRIMARY KEY AUTO INCREMENT 
 fizz_wooz，NVARCHAR（50）NOT NULL 
 fizz_buzz_jupiter，INT NOT NULL 
 fizz_buzz_neptune，NVARCHAR（100）NOT NULL 
  

如何让Hibernate执行这种基于注解的映射当我无法修改 Buzz ？

解决方案

for称为可嵌入。

  @Entity 
公共类Fizz {
 ... 
 
 @嵌入
私人Buzz嗡嗡声; 
 
 
  

你可以定义一个映射文件 em> Buzz ：

 < entity-mappings version = 1.0xmlns =http://java.sun.com/xml/ns/persistence/ormxmlns：xsi =http://www.w3.org/2001/XMLSchema-instance
 xsi ：schemaLocation =http://java.sun.com/xml/ns/persistence/orm 
 http://java.sun.com/xml/ns/persistence/orm_1_0.xsd\"> 
< embeddable class =... Buzz> 
<属性> 
< basic name =jupiter>< column name =fizz_buzz_jupiter/>< / basic> 
< basic name =neptune>< column name =fizz_buzz_neptune/>< / basic> 
< / attributes> 
< / embeddable> 
< / entity-mappings> 
  

您可以将该映射文件包含在 persistence.xml中

 < persistence-unit> 
< mapping-file> ... / orm.xml< / mapping-file> 
< / persistence-unit> 
  

如果您真的想为 Buzz ：您无法为其他类定义注释。这就是注释的含义：它们是 inline 并属于它们的类。否则，与映射文件相比，没有任何好处...

但是，您可以扩展 Buzz 并使用该文件 ：

：

  @Entity 
公共类Fizz {
。 .. 
 
 @Embedded 
私人BuzzExtension buzz; 
 
 
 $ b @Embeddable 
 @Access（AccessType.PROPERTY）
 public class BuzzExtension extends Buzz {
 @Column（name = fizz_buzz_jupiter）
 public int getJupiter（）{
 return super.getJupiter（）; 
 
 $ b @Column（name =fizz_buzz_neptune）
 public String getNeptune（）{
 return super.getNeptune（）; 
} 
 
} 
  

唯一缺点：您不能在 Fizz 中使用 Buzz 的实例。

I have the following entity I need to persist to a relational DB via Hibernate annotations:

@Entity
@Table(name="fizzes")
public class Fizz {
    @Id @GeneratedValue
    @Column(name="fizz_id")
    private int id;

    @Column(name="fizz_wooz")
    private String wooz;

    // ??? here I am unsure!
    private Buzz buzz;

    // Constructor, getters/setters down here, etc...
}

public class Buzz {
    private int jupiter;

    private String neptune;

    // Constructor, getters/setters down here, etc...
}

The problem with Buzz is:

• I do not want it to be its own entity/table. I want it to be a "value object/type" that gets mapped to the fizzes table (by way of adding columns to it)
• Buzz is from a third party library and hence I can't modify it

Hence the final result, in table form, that I'm looking for is:

[fizzes] table
==============
fizz_id, PRIMARY KEY AUTO INCREMENT
fizz_wooz, NVARCHAR(50) NOT NULL
fizz_buzz_jupiter, INT NOT NULL
fizz_buzz_neptune, NVARCHAR(100) NOT NULL

How can I get Hibernate to do this annotation-based mapping when I can't modify Buzz?

解决方案

What you are searching for is called Embeddable.

@Entity
public class Fizz {
    ...

    @Embedded
    private Buzz buzz;

}

And you can define a mapping file just for Buzz:

<entity-mappings version="1.0" xmlns="http://java.sun.com/xml/ns/persistence/orm" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
    xsi:schemaLocation="http://java.sun.com/xml/ns/persistence/orm    
                        http://java.sun.com/xml/ns/persistence/orm_1_0.xsd">
    <embeddable class="...Buzz">
        <attributes>
            <basic name="jupiter"><column name="fizz_buzz_jupiter"/></basic>
            <basic name="neptune"><column name="fizz_buzz_neptune"/></basic>
        </attributes>
    </embeddable>
</entity-mappings>

You can include that mapping file in your persistence.xml:

<persistence-unit>
    <mapping-file>.../orm.xml</mapping-file>
</persistence-unit>

If you really want to use annotations for Buzz: You can't define annotations for other classes. Thats the meaning of annotations: they are inline and belong to their class. Otherwise there would be no benefit compared to mapping files...

But you could extend Buzz and use that one with property access:

@Entity
public class Fizz {
    ...

    @Embedded
    private BuzzExtension buzz;

}

@Embeddable
@Access(AccessType.PROPERTY)
public class BuzzExtension extends Buzz {
    @Column(name="fizz_buzz_jupiter")
    public int getJupiter() {
        return super.getJupiter();
    }

    @Column(name="fizz_buzz_neptune")
    public String getNeptune() {
        return super.getNeptune();
    }

}

Only drawback: You can't use instances of Buzz in Fizz.

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