在使用mybatis的时候我们经常要用到联合查询，现在就对一表对多表和一对一表的xml文件配置进行说明
Student.xml

<resultMap type="many.one.entiry.Student" id="StudentResult">
    <id column="s_id" jdbcType="INTEGER" property="id"/>
    <result column="o_id" jdbcType="INTEGER" property="oid"/>
    <result column="s_name" jdbcType="VARCHAR" property="name"/>
    <result column="s_sex" jdbcType="VARCHAR" property="sex"/>
    <association property="teacher" javaType="many.one.entiry.Teacher" resultMap="many.one.mapper.TeacherMapper.TeacherResult" ></association>
    <collection property="courseList" ofType="many.one.entiry.Course"  resultMap="many.one.mapper.CourseMapper.CourseResult" />
  </resultMap>

StudentBean

public class Student {
    private Integer id;
    private String name;
    private String sex;
    private Integer oid;
    private Teacher teacher;//一对一
    private List<Course> courseList;//一对多
    public Student() {
    }
    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 String getSex() {
        return sex;
    }

    public void setSex(String sex) {
        this.sex = sex;
    }
    public Integer getOid() {
        return oid;
    }
    public void setOid(Integer oid) {
        this.oid = oid;
    }
    public Teacher getTeacher() {
        return teacher;
    }
    public void setTeacher(Teacher teacher) {
        this.teacher = teacher;
    }
    public Achievement getAchievement() {
        return achievement;
    }
    public void setAchievement(Achievement achievement) {
        this.achievement = achievement;
    }
    public List<Course> getCourseList() {
        return courseList;
    }
    public void setCourseList(List<Course> courseList) {
        this.courseList = courseList;
    }

    @Override
    public String toString() {
        return "Student [id=" + id + ", name=" + name + ", sex=" + sex
                + ", oid=" + oid + ", teacher=" + teacher + ", achievement="
                + achievement + ", courseList=" + courseList + "]";
    }

}

一对一在Bean中我们可以将其对象作为自身实体类的一个成员变量，一对多返回的结果是一个集合所以将其集合作为成员变量。
CourseBean

public class Course {
    private Integer c_id;
    private Integer c_sid;
    private String  biology;
    private String  physic;
    private String  chemistry;
    public Course(){}
    public Integer getC_id() {
        return c_id;
    }
    public void setC_id(Integer c_id) {
        this.c_id = c_id;
    }
    public Integer getC_sid() {
        return c_sid;
    }
    public void setC_sid(Integer c_sid) {
        this.c_sid = c_sid;
    }
    public String getBiology() {
        return biology;
    }
    public void setBiology(String biology) {
        this.biology = biology;
    }
    public String getPhysic() {
        return physic;
    }
    public void setPhysic(String physic) {
        this.physic = physic;
    }
    public String getChemistry() {
        return chemistry;
    }
    public void setChemistry(String chemistry) {
        this.chemistry = chemistry;
    }
    
    @Override
    public String toString() {
        return "Course [c_id=" + c_id + ", c_sid=" + c_sid + ", biology="
                + biology + ", physic=" + physic + ", chemistry=" + chemistry
                + "]";
    }
    
}

TeacherBean

public class Teacher {
    private Integer t_id;
    private String  username;
    private String  password;
    public Integer getT_id() {
        return t_id;
    }
    public void setT_id(Integer t_id) {
        this.t_id = t_id;
    }
    public String getUsername() {
        return username;
    }
    public void setUsername(String username) {
        this.username = username;
    }
    public String getPassword() {
        return password;
    }
    public void setPassword(String password) {
        this.password = password;
    }
    @Override
    public String toString() {
        return "Teacher [t_id=" + t_id + ", username=" + username
                + ", password=" + password + "]";
    }
}

Course.xml

<resultMap type="many.one.entiry.Course" id="CourseResult">
        <id column="c_id" jdbcType="INTEGER" property="c_id" />
        <result column="c_sid" jdbcType="INTEGER" property="c_sid" />
        <result column="c_biology" jdbcType="VARCHAR" property="biology" />
        <result column="c_physic" jdbcType="VARCHAR" property="physic" />
        <result column="c_chemistry" jdbcType="VARCHAR" property="chemistry" />     
</resultMap>

teacher.xml

<resultMap type="many.one.entiry.Teacher" id="TeacherResult">
        <id column="t_id" jdbcType="INTEGER" property="t_id" />
        <id column="t_name" jdbcType="VARCHAR" property="username" />
        <result column="t_password" jdbcType="VARCHAR" property="password" />
</resultMap>

association标签是用来配置一对一表查询的，collection是配置一对多表查询的。
一对一查询中mybatis会将查询结果封装到相应的对象中，如teacher对象，而一对多将返回一个List集合如List<courseList>.