07.MyBatis中的关联查询

关联查询：

一对一：

两种方式实现:

1.通过业务扩展的方式进行一对一查询，新建一个实体类，继承其中属性多的一个，然后写上另一个类中的属性：

实体类:

 映射文件:

1 <!-- 业务扩展的方式进行一对一查询，创建一个新的实体类继承属性多的一方然后重写属性少的一方 -->
2   <select id="queryStudentWithOO" parameterType="int" resultType="StudentBusiness">
3     select * from student s inner join studentcard c on s.sid = c.cid and sid = #{sid}
4   </select>

测试类:

 1 //一对一查寻
 2     public static void queryStudentWithOO() throws IOException {
 3         //读取配置文件
 4         Reader reader = Resources.getResourceAsReader("conf.xml");
 5         //创建sqlSessionFactory
 6         SqlSessionFactory sessionFactory = new SqlSessionFactoryBuilder().build(reader);
 7         //获取session
 8         SqlSession session = sessionFactory.openSession();
 9         //定位映射文件
10         studentMapper studentMapper = session.getMapper(studentMapper.class);
11         //定位sql语句并执行
12         StudentBusiness studentBusiness = studentMapper.queryStudentWithOO(3);
13         //提交事务
14         session.commit();
15         System.out.println(studentBusiness);
16         //关闭连接
17         session.close();
18     }

2.通过ResultMap的方式实现一对一

然后在映射文件中使用association进行对象属性的映射:

实体类:

配置文件:

 1  <select id="queryStudentWithMap" parameterType="int" resultMap="StudentBusiness1">
 2     select * from student s inner join studentcard c on s.sid = c.cid and sid = #{sid}
 3   </select>
 4 <resultMap type="StudentBusiness" id="StudentBusiness1">
 5   <id property="sid" column="sid"/>
 6   <result property="sname" column="sname"/>
 7   <result property="age" column="age"/>
 8   <result property="sex" column="sex"/>
 9   <result property="cid" column="cid"/>
10   <result property="stuInfo" column="stuInfo"/>
11       <association property="address" javaType="Address">
12           <result property="homeAddress" column="homeaddress"/>
13           <result property="schoolAddress" column="schooladdress"/>
14       </association>
15   </resultMap>

测试类:

 1 //一对一查寻，使用ResultMap的方式
 2     public static void queryStudentWithMap() throws IOException {
 3         //读取配置文件
 4         Reader reader = Resources.getResourceAsReader("conf.xml");
 5         //创建sqlSessionFactory
 6         SqlSessionFactory sessionFactory = new SqlSessionFactoryBuilder().build(reader);
 7         //获取session
 8         SqlSession session = sessionFactory.openSession();
 9         //定位映射文件
10         studentMapper studentMapper = session.getMapper(studentMapper.class);
11         //定位sql语句并执行
12         StudentBusiness studentBusiness = studentMapper.queryStudentWithMap(3);
13         //提交事务
14         session.commit();
15         System.out.println(studentBusiness);
16         //关闭连接
17         session.close();
18     }

2.一对多:

一个班级对应多个学生，应在班级的实体类中定义一个学生的属性,然后在映射文件中使用collection进行对象属性集合进行映射:

实体类:

 

配置文件：

 1  <!-- 一对多查询 -->
 2   <select id="queryStudentWithOM" parameterType="int" resultMap="Studentclass1">
 3     select * from student s inner join studentclass c on s.cno = c.cno and c.cno = #{cno}
 4   </select>
 5   
 6   <resultMap type="StudentClass" id="Studentclass1">
 7       <id property="cno" column="cno"/>
 8       <result property="cname" column="cname"/>
 9       <!-- 循环集合用collection，属性值写集合属性名，类型写集合中的元素的类型并且使用的是ofType -->
10       <collection property="students" ofType="student">
11           <result property="sname" column="sname"/>
12           <result property="age" column="age"/>
13           <result property="sex" column="sex"/>
14       </collection>
15   </resultMap>

测试类:

 1 //一对多查寻
 2     public static void queryStudentWithOM() throws IOException {
 3         //读取配置文件
 4         Reader reader = Resources.getResourceAsReader("conf.xml");
 5         //创建sqlSessionFactory
 6         SqlSessionFactory sessionFactory = new SqlSessionFactoryBuilder().build(reader);
 7         //获取session
 8         SqlSession session = sessionFactory.openSession();
 9         //定位映射文件
10         studentMapper studentMapper = session.getMapper(studentMapper.class);
11         //定位sql语句并执行
12          StudentClass studentClass = studentMapper.queryStudentWithOM(2);
13          System.out.println(studentClass);
14         //提交事务
15         session.commit();
16         List<Student> students = studentClass.getStudents();
17         for (Student student : students) {
18             System.out.print(studentClass.getCno() + "," + studentClass.getCname() + ",");
19             System.out.println(student.getSname()+"," +student.getAge()+"," +student.getSex());
20         }
21         //关闭连接
22         session.close();
23     }