级联是resultMap中的配置。

级联分为3种

• 鉴别器（discrimination）：根据某些条件采用具体实现具体实现类级联，如体检表根据性别去区分
• 一对一：学生和学生证
• 一对多：班主任和学生。

bean:
public class Employee {

private Long id;  
private String realName;  
private SexEnum sex = null;  
private Date birthday;  
private String mobile;  
private String email;  
private String position;  
private String note;  
//工牌按一对一级联  
private WorkCard workCard;  
//雇员任务，一对多级联  
private List<EmployeeTask> employeeTaskList = null;

public Long getId() {  
    return id;  
}  
public void setId(Long id) {  
    this.id = id;  
}  
public String getRealName() {  
    return realName;  
}  
public void setRealName(String realName) {  
    this.realName = realName;  
}  
public SexEnum getSex() {  
    return sex;  
}  
public void setSex(SexEnum sex) {  
    this.sex = sex;  
}  
public Date getBirthday() {  
    return birthday;  
}  
public void setBirthday(Date birthday) {  
    this.birthday = birthday;  
}  
public String getMobile() {  
    return mobile;  
}  
public void setMobile(String mobile) {  
    this.mobile = mobile;  
}  
public String getEmail() {  
    return email;  
}  
public void setEmail(String email) {  
    this.email = email;  
}  
public String getPosition() {  
    return position;  
}  
public void setPosition(String position) {  
    this.position = position;  
}  
public String getNote() {  
    return note;  
}  
public void setNote(String note) {  
    this.note = note;  
}  
public WorkCard getWorkCard() {  
    return workCard;  
}  
public void setWorkCard(WorkCard workCard) {  
    this.workCard = workCard;  
}  
public List<EmployeeTask> getEmployeeTaskList() {  
    return employeeTaskList;  
}  
public void setEmployeeTaskList(List<EmployeeTask> employeeTaskList) {  
    this.employeeTaskList = employeeTaskList;  
}  

}

public class FemaleEmployee extends Employee {

private FemaleHealthForm femaleHealthForm = null;

public FemaleHealthForm getFemaleHealthForm() {  
    return femaleHealthForm;  
}

public void setFemaleHealthForm(FemaleHealthForm femaleHealthForm) {  
    this.femaleHealthForm = femaleHealthForm;  
}  

}

public class MaleEmployee extends Employee {

private MaleHealthForm maleHealthForm = null;

public MaleHealthForm getMaleHealthForm() {  
    return maleHealthForm;  
}

public void setMaleHealthForm(MaleHealthForm maleHealthForm) {  
    this.maleHealthForm = maleHealthForm;  
}  

}

public class WorkCard {
private Long id;
private Long empId;
private String realName;
private String department;
private String mobile;
private String position;
private String note;

}

public class EmployeeTask {
private Long id;
private Long empId;
private Task task = null;
private String taskName;
private String note;
}

mapper:
public interface EmployeeMapper {

public Employee getEmployee(Long id);

public Employee getEmployee2(Long id);  

}

XML:










//应用另外一个 xml map中 id为"getWorkCardByEmpId"的select

    <collection property="employeeTaskList" column="id"//一对多  
        fetchType="eager"  
        select="com.ssm.chapter5.mapper.EmployeeTaskMapper.getEmployeeTaskByEmpId" />  
    <discriminator javaType="long" column="sex">  
        <case value="1" resultMap="maleHealthFormMapper" />//鉴别器级联  
        <case value="2" resultMap="femaleHealthFormMapper" />  
    </discriminator>  
</resultMap>

<resultMap type="com.ssm.chapter5.pojo.FemaleEmployee" id="femaleHealthFormMapper"  
    extends="employee">  
    <association property="femaleHealthForm" column="id"  
        select="com.ssm.chapter5.mapper.FemaleHealthFormMapper.getFemaleHealthForm" />  
</resultMap>

<resultMap type="com.ssm.chapter5.pojo.MaleEmployee" id="maleHealthFormMapper"  
    extends="employee">  
    <association property="maleHealthForm" column="id"  
        select="com.ssm.chapter5.mapper.MaleHealthFormMapper.getMaleHealthForm" />  
</resultMap>

<select id="getEmployee" parameterType="long" resultMap="employee">  
    select  
    id, real\_name as realName, sex, birthday, mobile, email, position,  
    note from t\_employee where id = #{id}  
</select>

<resultMap id="employee2" type="com.ssm.chapter5.pojo.Employee">  
    <id column="id" property="id" />  
    <result column="real\_name" property="realName" />  
    <result column="sex" property="sex"  
        typeHandler="com.ssm.chapter5.typeHandler.SexTypeHandler" />  
    <result column="birthday" property="birthday" />  
    <result column="mobile" property="mobile" />  
    <result column="email" property="email" />  
    <result column="position" property="position" />  
    <association property="workCard" javaType="com.ssm.chapter5.pojo.WorkCard"/一对一级联  
        column="id">  
        <id column="wc\_id" property="id" />  
        <result column="id" property="empId" />  
        <result column="wc\_real\_name" property="realName" />  
        <result column="wc\_department" property="department" />  
        <result column="wc\_mobile" property="mobile" />  
        <result column="wc\_position" property="position" />  
        <result column="wc\_note" property="note" />  
    </association>  
    <collection property="employeeTaskList" ofType="com.ssm.chapter5.pojo.EmployeeTask"//一对多级联  
        column="id">  
        <id column="et\_id" property="id" />  
        <result column="id" property="empId" />  
        <result column="task\_name" property="taskName" />  
        <result column="note" property="note" />  
        <association property="task" javaType="com.ssm.chapter5.pojo.Task"  
            column="et\_task\_id">  
            <id column="t\_id" property="id" />  
            <result column="t\_title" property="title" />  
            <result column="t\_context" property="context" />  
            <result column="t\_note" property="note" />  
        </association>  
    </collection>  
    <discriminator javaType="int" column="sex"> //sex鉴别器级联male/female  
        <case value="1" resultMap="maleHealthFormMapper2" />  
        <case value="2" resultMap="femaleHealthFormMapper2" />  
    </discriminator>  
</resultMap>

<resultMap type="com.ssm.chapter5.pojo.MaleEmployee" id="maleHealthFormMapper2"  
    extends="employee2">  
    <association property="maleHealthForm" column="id"  
        javaType="com.ssm.chapter5.pojo.MaleHealthForm">  
        <id column="h\_id" property="id" />  
        <result column="h\_heart" property="heart" />  
        <result column="h\_liver" property="liver" />  
        <result column="h\_spleen" property="spleen" />  
        <result column="h\_lung" property="lung" />  
        <result column="h\_kidney" property="kidney" />  
        <result column="h\_prostate" property="prostate" />  
        <result column="h\_note" property="note" />  
    </association>  
</resultMap>

<resultMap type="com.ssm.chapter5.pojo.FemaleEmployee" id="femaleHealthFormMapper2"  
    extends="employee2">  
    <association property="femaleHealthForm" column="id"  
        javaType="com.ssm.chapter5.pojo.FemaleHealthForm">  
        <id column="h\_id" property="id" />  
        <result column="h\_heart" property="heart" />  
        <result column="h\_liver" property="liver" />  
        <result column="h\_spleen" property="spleen" />  
        <result column="h\_lung" property="lung" />  
        <result column="h\_kidney" property="kidney" />  
        <result column="h\_uterus" property="uterus" />  
        <result column="h\_note" property="note" />  
    </association>  
</resultMap>

<select id="getEmployee2" parameterType="long" resultMap="employee2">  
    select  
    emp.id, emp.real\_name, emp.sex, emp.birthday,  
    emp.mobile, emp.email,  
    emp.position, emp.note,  
    et.id as et\_id, et.task\_id as et\_task\_id,  
    et.task\_name as et\_task\_name,  
    et.note as et\_note,  
    if (emp.sex = 1,  
    mhf.id, fhf.id) as h\_id,  
    if (emp.sex = 1, mhf.heart, fhf.heart) as  
    h\_heart,  
    if (emp.sex = 1, mhf.liver, fhf.liver) as h\_liver,  
    if (emp.sex  
    = 1, mhf.spleen, fhf.spleen) as h\_spleen,  
    if (emp.sex = 1, mhf.lung,  
    fhf.lung) as h\_lung,  
    if (emp.sex = 1, mhf.kidney, fhf.kidney) as  
    h\_kidney,  
    if (emp.sex = 1, mhf.note, fhf.note) as h\_note,  
    mhf.prostate  
    as h\_prostate, fhf.uterus as h\_uterus,  
    wc.id wc\_id, wc.real\_name  
    wc\_real\_name, wc.department wc\_department,  
    wc.mobile wc\_mobile,  
    wc.position wc\_position, wc.note as wc\_note,  
    t.id as t\_id, t.title as  
    t\_title, t.context as t\_context, t.note as t\_note  
    from t\_employee emp  
    left join t\_employee\_task et on emp.id = et.emp\_id  
    left join  
    t\_female\_health\_form fhf on emp.id = fhf.emp\_id  
    left join  
    t\_male\_health\_form mhf on emp.id = mhf.emp\_id  
    left join t\_work\_card wc  
    on emp.id = wc.emp\_id  
    left join t\_task t on et.task\_id = t.id  
    where  
    emp.id = #{id}  
</select>  

test：

public static void testGetEmployee() {
SqlSession sqlSession = null;
try {
sqlSession = SqlSessionFactoryUtils.openSqlSession();
EmployeeMapper employeeMapper = sqlSession.getMapper(EmployeeMapper.class);
Employee employee = employeeMapper.getEmployee(1L);
System.out.println(employee.getWorkCard().getPosition());
} catch(Exception ex) {
ex.printStackTrace();
} finally {
if (sqlSession != null) {
sqlSession.close();
}
}
}

public static void testGetEmployee2() {  
    SqlSession sqlSession = null;  
    try {  
        sqlSession = SqlSessionFactoryUtils.openSqlSession();  
        EmployeeMapper employeeMapper = sqlSession.getMapper(EmployeeMapper.class);  
        Employee employee = employeeMapper.getEmployee2(1L);  
        System.out.println(employee.getWorkCard().getPosition());  
    } catch(Exception ex) {  
        ex.printStackTrace();  
    } finally {  
        if (sqlSession != null) {  
            sqlSession.close();  
        }  
    }  
}