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：
因此，我要找的表格的最终结果是：
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 =java.sun/xml/ns/persistence/ormxmlns：xsi =www.w3/2001/XMLSchema-instance xsi ：schemaLocation =java.sun/xml/ns/persistence/orm java.sun/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 NULLHow 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="java.sun/xml/ns/persistence/orm" xmlns:xsi="www.w3/2001/XMLSchema-instance" xsi:schemaLocation="java.sun/xml/ns/persistence/orm java.sun/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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