Hibernate 多表关联映射- Hibernate中使用的集合类型(set,list,array,bag,map)

Set类型的使用：

<hibernate-mapping package="cn.model">
<class name="Department" table="DEPARTMENT">
<id name="id" column="ID">
<generator class="native"></generator>
</id>
<property name="name" column="NAME" type="java.lang.String" />
<set name="employees">
<key column="DEPT_ID" />
<one-to-many class="Employee"/>
</set>
</class>
</hibernate-mapping>

Set是最常见的在Hibernate中对集合进行映射的类型，其配置也很简单;

List类型的使用：

<hibernate-mapping package="cn.model">
<class name="Department" table="DEPARTMENT">
<id name="id" column="ID">
<generator class="native"></generator>
</id>
<property name="name" column="NAME" type="java.lang.String" />
<list name="employees">
<key column="DEPT_ID" />
<list-index column="EMPLOYEE_INDEX" />
<one-to-many class="Employee"/>
</list>
</class>
</hibernate-mapping>

使用List进行集合映射有一点特殊，List是按顺序进行存入所以Hibernate还需要在表中新增一个排序列来存入数据存入的顺序：

Hibernate:
create table EMPLOYEE (
ID integer not null auto_increment,
NAME varchar(255),
DEPT_ID integer,
EMPLOYEE_INDEX integer,
primary key (ID)
)

Bag类型的使用：

如果想使用List，但又不想在表中产生排序列，那可以使用Bag ；在实体中还是使用List，但在Hbm.xml映射文件中将list改为bag即可：

public class Department {

private Integer id;
private String name;
private List<Employee> employees;

public Integer getId() {
return id;
}
public void setId(Integer id) {
this.id = id;
}
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
public List<Employee> getEmployees() {
return employees;
}
public void setEmployees(List<Employee> employees) {
this.employees = employees;
}

}

<hibernate-mapping package="cn.model">
<class name="Department" table="DEPARTMENT">
<id name="id" column="ID">
<generator class="native"></generator>
</id>
<property name="name" column="NAME" type="java.lang.String" />
<bag name="employees">
<key column="DEPT_ID" />
<one-to-many class="Employee"/>
</bag>
</class>
</hibernate-mapping>

Map类型的使用:

使用Map类型对集合进行映射，程序中用的不多，但是也有存在，配置相比Set和Bag较麻烦一点：

<hibernate-mapping package="cn.model">
<class name="Department" table="DEPARTMENT">
<id name="id" column="ID">
<generator class="native"></generator>
</id>
<property name="name" column="NAME" type="java.lang.String" />
<map name="employees">
<key column="DEPT_ID" />
<map-key type="string" column="name" />
<one-to-many class="Employee"/>
</map>
</class>
</hibernate-mapping>

数组Object[]类型的使用:

数组类型映射和List有点类似，都是需要一个排序的列：

public class Department {

private Integer id;
private String name;
private Employee[] employees;

public Integer getId() {
return id;
}
public void setId(Integer id) {
this.id = id;
}
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
public Employee[] getEmployees() {
return employees;
}
public void setEmployees(Employee[] employees) {
this.employees = employees;
}

}

<hibernate-mapping package="cn.model">
<class name="Department" table="DEPARTMENT">
<id name="id" column="ID">
<generator class="native"></generator>
</id>
<property name="name" column="NAME" type="java.lang.String" />
<array name="employees">
<key column="DEPT_ID" />
<list-index column="EMPLOYEE_INDEX" />
<one-to-many class="Employee"/>
</array>
</class>
</hibernate-mapping>

总结：