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：