mybatis中的关联查询

Student2.java页面
 //一对一：通过查询学生信息关联来查到学生详细信息
    private StudentInFo studentInFo;

StudemtMapper2.java页面
 //通过查询学生信息关联来查到学生详细信息
    Student2 selectByIdss(Integer id);

StudentMapper2.xml页面

<resultMap id="StudentResult" type="Student2">
    <id column="id" property="id"></id>
    <result property="studentName" column="name"></result>
    <result property="classid" column="classid"></result>
    <result property="version" column="version"></result>
    <association property="studentInFo" javaType="StudentInFo" column="id"
                 select="com.seecen.mybatis3.mapper.StudentInFoMapper.selectById"></association>
</resultMap>
<select id="selectByIdss" resultMap="StudentResult">
    select * from h_student where id=#{id}
</select>

StudentInFoMapper.java页面
  @Select("select * from h_student_info where id=#{id}")
    StudentInFo selectById(Integer id);

测试代码文件：
 System.out.println("============测试查询学生信息时把学生详细信息查出=============");
        Student2 student23 = mapper.selectByIdss(2);
        System.out.println(student23);
        System.out.println(student23.getStudentInFo());

HClass.java文件：
 //一对多：查询班级的时候把班级下的所有学生查询出来
    private List<Student2> student2s;

HClassMapper.java文件
//查询班级的时候把班级下的所有学生查询出来
    HClass selectWithStudent(Integer id);

HClassMapper.xml文件：
   <resultMap id="studentResult" type="HClass">
        <id column="id" property="id"></id>
        <result property="name" column="name"></result>
        <result property="city" column="city"></result>
        <collection property="student2s" column="id" ofType="Student2"
                    select="com.seecen.mybatis3.mapper.StudentMapper2.selectByClassId"
        ></collection>
    </resultMap>
    <select id="selectWithStudent" resultMap="studentResult">
        select * from h_class where id=#{id}
    </select>

StuentMapper2.java文件：
 //查询班级的时候把学生信息查询出来
    List<Student2> selectByClassId(Integer id);

StudentMapper.xml文件：
<select id="selectByClassId" resultType="Student2">
        select t2.id,t2.name as studentName,t2.classid,t2.version from h_class t1,h_student t2 where
        t1.id=t2.classid and t1.id=#{id}
    </select>

测试代码文件：
System.out.println("==========查询班级的时候把对应的学生查询出来==========");
        HClass hClass1=mapper.selectWithStudent(21);
        System.out.println(hClass1);
        System.out.println(hClass1.getStudent2s());

HClass.java文件：
 //多对多
    // 1 hclass 写一个查询（resultMap ）
    // 2 在resultMap配置 关联查询
    // 3 teacherMapper写一个根据班级ID查询老师信息的方法
    private List<Teacher> teachers;

HClassMapper.java文件：
//查询班级信息并关联查询老师信息的
    HClass selectWithTeacher(Integer id);

HClassMapper.xml文件：
    <resultMap id="classResult" type="HClass">
        <id column="id" property="id"></id>
        <result property="name" column="name"></result>
        <result property="city" column="city"></result>
<!--        关联查询,返回集合-->
<!--     ofType:指定集合中的泛型类型   -->
        <collection property="teachers" column="id" ofType="Teacher"
                    select="com.seecen.mybatis3.mapper.TeacherMapper.selectByClassId"
        ></collection>
    </resultMap>
    <select id="selectWithTeacher" resultMap="classResult">
        select * from h_class where id=#{id}
    </select>

TeacherMapper.java文件：
//班级信息查询老师信息
    List<Teacher> selectByClassId(Integer id);

TeacherMapper.xml文件：
   <select id="selectByClassId" resultType="Teacher">
        select t1.* from h_teacher t1,h_class_teacher t2 where
        t1.id=t2.teacherid and t2.classid=#{classid}
    </select>

测试代码文件：
System.out.println("=======查询班级的时候把对应的老师查询出来=========");
        HClass hClass = mapper.selectWithTeacher(21);
        System.out.println(hClass);
        System.out.println(hClass.getTeachers());

在Student2.java页面
//多对一 组合/继承
    private HClass hClass; 

在StudentMapper2.java页面

Student2 selectByIdMappingWithResultMap(Integer id);

在Student2Mapper.xml页面  

<!--定义结果集映射，通过该映射来指定表的列与类的属性的映射关系-->
<!--id:唯一表示; type:关联到实体类-->
    <resultMap id="studentResultMap" type="Student2">
        <!--id:配置主键与实体类中属性的映射关系-->
        <id column="ID" property="id" jdbcType="DECIMAL"></id>
        <!--result:配置非主键列-->
        <result column="name" property="studentName"></result>
        <result column="classid" property="classid"></result>
        <result column="version" property="version"></result>
        <!--配置关联查询，返回单个结果
           javaType:指定返回的java类型  select：指定关联的查询(关联到另外一个Mapper的查询方法)
           column:指定要传递的列(会将该列的值，当做参数传递到关联的查询方法中)
        -->
        <association property="hClass" javaType="HClass" column="classid"
                     select="com.seecen.mybatis3.mapper.HClassMapper.selectById"></association>
    </resultMap>
    <!--resultMap：指定返回的结果集映射的ID值-->
    <select id="selectByIdMappingWithResultMap" resultMap="studentResultMap">
        select * from h_student where id=#{id}
    </select>

HClassMapper.java文件：
HClass selectById(Integer id);

HClassMapper.xml文件：
  <select id="selectById" parameterType="integer" resultType="HClass">
           select * from h_class where id=#{id}
    </select>

测试代码文件：
System.out.println("===========测试关联查询==============");
        Student2 student22 = mapper.selectByIdMappingWithResultMap(6);
        System.out.println(student22);
        System.out.println(student22.gethClass());