23.1. Employer（雇主)/Employee(雇员)

下面关于Employer 和 Employee的关系模型使用了一个真实的实体类 (Employment)来表述，这是因为对于相同的雇员和雇主可能会有多个雇佣时间段。 对于金额和雇员姓名，用Components建模。

23.1. Employer（雇主)/Employee(雇员) - 图1

映射文件可能是这样:

  1. <hibernate-mapping>
  3.     <class name="Employer" table="employers">
  4.         <id name="id">
  5.             <generator class="sequence">
  6.                 <param name="sequence">employer_id_seq</param>
  7.             </generator>
  8.         </id>
  9.         <property name="name"/>
  10.     </class>
  12.     <class name="Employment" table="employment_periods">
  14.         <id name="id">
  15.             <generator class="sequence">
  16.                 <param name="sequence">employment_id_seq</param>
  17.             </generator>
  18.         </id>
  19.         <property name="startDate" column="start_date"/>
  20.         <property name="endDate" column="end_date"/>
  22.         <component name="hourlyRate" class="MonetaryAmount">
  23.             <property name="amount">
  24.                 <column name="hourly_rate" sql-type="NUMERIC(12, 2)"/>
  25.             </property>
  26.             <property name="currency" length="12"/>
  27.         </component>
  29.         <many-to-one name="employer" column="employer_id" not-null="true"/>
  30.         <many-to-one name="employee" column="employee_id" not-null="true"/>
  32.     </class>
  34.     <class name="Employee" table="employees">
  35.         <id name="id">
  36.             <generator class="sequence">
  37.                 <param name="sequence">employee_id_seq</param>
  38.             </generator>
  39.         </id>
  40.         <property name="taxfileNumber"/>
  41.         <component name="name" class="Name">
  42.             <property name="firstName"/>
  43.             <property name="initial"/>
  44.             <property name="lastName"/>
  45.         </component>
  46.     </class>
  48. </hibernate-mapping>

用SchemaExport生成表结构。

  1. create table employers (
  2.     id BIGINT not null, 
  3.     name VARCHAR(255), 
  4.     primary key (id)
  5. )
  7. create table employment_periods (
  8.     id BIGINT not null,
  9.     hourly_rate NUMERIC(12, 2),
  10.     currency VARCHAR(12), 
  11.     employee_id BIGINT not null, 
  12.     employer_id BIGINT not null, 
  13.     end_date TIMESTAMP, 
  14.     start_date TIMESTAMP, 
  15.     primary key (id)
  16. )
  18. create table employees (
  19.     id BIGINT not null, 
  20.     firstName VARCHAR(255), 
  21.     initial CHAR(1), 
  22.     lastName VARCHAR(255), 
  23.     taxfileNumber VARCHAR(255), 
  24.     primary key (id)
  25. )
  27. alter table employment_periods 
  28.     add constraint employment_periodsFK0 foreign key (employer_id) references employers
  29. alter table employment_periods 
  30.     add constraint employment_periodsFK1 foreign key (employee_id) references employees
  31. create sequence employee_id_seq
  32. create sequence employment_id_seq
  33. create sequence employer_id_seq