23.2. Author(作家)/Work(作品)

考虑下面的Work,Author 和 Person模型的关系。 我们用多对多关系来描述Work 和 Author， 用一对一关系来描述Author 和 Person， 另一种可能性是Author继承Person。

23.2. Author(作家)/Work(作品) - 图1

下面的映射文件正确的描述了这些关系：

  1. <hibernate-mapping>
  3.     <class name="Work" table="works" discriminator-value="W">
  5.         <id name="id" column="id">
  6.             <generator class="native"/>
  7.         </id>
  8.         <discriminator column="type" type="character"/>
  10.         <property name="title"/>
  11.         <set name="authors" table="author_work">
  12.             <key column name="work_id"/>
  13.             <many-to-many class="Author" column name="author_id"/>
  14.         </set>
  16.         <subclass name="Book" discriminator-value="B">
  17.             <property name="text"/>
  18.         </subclass>
  20.         <subclass name="Song" discriminator-value="S">
  21.             <property name="tempo"/>
  22.             <property name="genre"/>
  23.         </subclass>
  25.     </class>
  27.     <class name="Author" table="authors">
  29.         <id name="id" column="id">
  30.             <!-- The Author must have the same identifier as the Person -->
  31.             <generator class="assigned"/> 
  32.         </id>
  34.         <property name="alias"/>
  35.         <one-to-one name="person" constrained="true"/>
  37.         <set name="works" table="author_work" inverse="true">
  38.             <key column="author_id"/>
  39.             <many-to-many class="Work" column="work_id"/>
  40.         </set>
  42.     </class>
  44.     <class name="Person" table="persons">
  45.         <id name="id" column="id">
  46.             <generator class="native"/>
  47.         </id>
  48.         <property name="name"/>
  49.     </class>
  51. </hibernate-mapping>

映射中有4个表。works, authors 和 persons 分别保存着work，author和person的数据。author_work是authors和works的关联表。 表结构是由SchemaExport生成的。

  1. create table works (
  2.     id BIGINT not null generated by default as identity, 
  3.     tempo FLOAT, 
  4.     genre VARCHAR(255), 
  5.     text INTEGER, 
  6.     title VARCHAR(255), 
  7.     type CHAR(1) not null, 
  8.     primary key (id)
  9. )
  11. create table author_work (
  12.     author_id BIGINT not null, 
  13.     work_id BIGINT not null, 
  14.     primary key (work_id, author_id)
  15. )
  17. create table authors (
  18.     id BIGINT not null generated by default as identity, 
  19.     alias VARCHAR(255), 
  20.     primary key (id)
  21. )
  23. create table persons (
  24.     id BIGINT not null generated by default as identity, 
  25.     name VARCHAR(255), 
  26.     primary key (id)
  27. )
  29. alter table authors 
  30.     add constraint authorsFK0 foreign key (id) references persons
  31. alter table author_work 
  32.     add constraint author_workFK0 foreign key (author_id) references authors
  33. alter table author_work
  34.     add constraint author_workFK1 foreign key (work_id) references works