MyBatis关联查询，多对一与一对多

多对一查询：

表结构：

CREATE TABLE `teacher` (
  `id` INT(10) NOT NULL,
  `name` VARCHAR(30) DEFAULT NULL,
  PRIMARY KEY (`id`)
)#教师表
CREATE TABLE `student` (
  `id` INT(10) NOT NULL,
  `name` VARCHAR(30) DEFAULT NULL,
  `tid` INT(10) DEFAULT NULL,
  PRIMARY KEY (`id`),
  KEY `fktid` (`tid`),
  CONSTRAINT `fktid` FOREIGN KEY (`tid`) REFERENCES `teacher` (`id`)
)#学生表

实体类：

public class Student {
    private  int id;
    private String name;
    private Teacher teacher;
}

public class Teacher {
    private int id;
    private String name;
}

查询需求：（学生id，学生姓名，教师id，教师姓名）

sql语句：

select *from`student`, `teacher`where`teacher`.`id`=`student`.`tid`;

在mybatis中的接口：

public interface StudentMapper {
    public List<Student> getStudent1();
    public List<Student> getStudent2();
    public List<Student> getStudent3();
}

编写maper文件：

   <select id="getStudent1" resultMap="StudentTeacher1">
        select * from student;
    </select>
    <resultMap id="StudentTeacher1" type="Student">
        <result property="id" column="id"></result>
        <result property="name" column="name"/>
        <association property="teacher" column="tid" javaType="Teacher" select="getTeacherName"></association>
    </resultMap>
    <select id="getTeacherName" resultType="Teacher">
        select *from teacher where id=#{id};
    </select>


    <select id="getStudent2" resultMap="StudentTeacher2">
        select s.id sid,s.name sname,t.id tid,t.name tname
        from student s,teacher t
        where s.tid=t.id;
    </select>
    <resultMap id="StudentTeacher2" type="Student">
        <result property="id" column="sid"/>
        <result property="name" column="sname"/>
        <association property="teacher" javaType="Teacher">
            <result property="name" column="tname"/>
            <result property="id" column="tid"/>
        </association>
    </resultMap>

    <select id="getStudent3" resultMap="StudentTeacher3">
        select s.*,t.id tid,t.name tname
        from student s,teacher t
        where s.tid=t.id;
    </select>
    <resultMap id="StudentTeacher3" type="Student">
        <result property="teacher.id" column="tid"/>
        <result property="teacher.name" column="tname"/>
    </resultMap>

一对多查询：

实体类：

public class Student {
    private  int id;
    private String name;
    private int tid;
}
public class Teacher {
    private int id;
    private String name;
    private List<Student> studentList;
}

接口：

public interface TeacherMapper {
    Teacher getTeacherById1(@Param("tid") int id);
    Teacher getTeacherById2(@Param("tid") int id);
}

xml配置：

<select id="getTeacherById1" resultMap="TeacherStudent1">
    select s.id sid,s.name sname,t.id tid,t.name tname
    from student s,teacher t
    where s.tid=t.id and t.id=#{tid};
</select>
<resultMap id="TeacherStudent1" type="Teacher">
    <result property="id" column="tid"/>
    <result property="name" column="tname"/>
    <collection property="studentList" ofType="Student">
        <result property="id" column="sid"/>
        <result property="name" column="sname"/>
        <result property="tid" column="tid"/>
    </collection>
</resultMap>

<select id="getTeacherById2" resultMap="TeacherStudent2">
    select * from teacher where id=#{tid};
</select>
<resultMap id="TeacherStudent2" type="Teacher">
    <collection property="studentList" javaType="ArrayList" ofType="Student" select="getStudentByTeacherId" column="id"/>
</resultMap>
<select id="getStudentByTeacherId" resultType="Student">
    select * from student where tid = #{id};
</select>