一對多的級聯

CREATE TABLE f_class(
c_id INT PRIMARY KEY AUTO_INCREMENT COMMENT 's_id',
CODE VARCHAR(20) NOT NULL COMMENT '編號',
NAME VARCHAR(20) NOT NULL COMMENT '名稱'
);
INSERT INTO f_class(CODE,NAME) VALUES ('1401','Software Engineering'
 
);

CREATE TABLE f_student(
s_id INT PRIMARY KEY AUTO_INCREMENT COMMENT 's_id',
s_NAME VARCHAR(20) NOT NULL COMMENT '名字',
sex VARCHAR(20) NOT NULL COMMENT '性別',
age INT NOT NULL COMMENT '年齡',
class_id INT,
FOREIGN KEY (class_id) REFERENCES f_class(id)
);
INSERT INTO f_student (s_NAME,sex,age,class_id) VALUES
 
 ('lazy','boy',20,1);
INSERT INTO f_student (s_NAME,sex,age,class_id) VALUES ('rose','girl',19,1);
INSERT INTO f_student (s_NAME,sex,age,class_id) VALUES ('joh','boy',19,1);
INSERT INTO f_student (s_NAME,sex,age,class_id) VALUES ('miss','girl',20,1);

建立POJO物件，都省略類 set和get方法。
Grade.java

public class
 
 Grade implements Serializable{
    private Integer c_id;
    private String code;
    private String name;
    //班級和學生一對多的關係，一個班級可以有多個學生
    private List<Student> students;
  } 

Student.java

public class Student implements Serializable {
    private Integer s_id;
    private String s_name;
    private String sex;
    private Integer age;
}

對映檔案GradeMapper.xml

<mapper namespace="com.stumybatis.dao.GradeDao">
    <select id="selectGradeById" parameterType="int" resultMap="gradeStudent">
        SELECT * from f_class c,f_student s  where c.c_id=#{c_id} and s.class_id=c.c_id
    </select>
    <resultMap id="gradeStudent" type="com.stumybatis.pojo.Grade">
        <id property="c_id" column="c_id"/>
        <result property="code" column="code"/>
        <result property="name" column="name"/>
        <!--collection表示一對多的關係-->
        <collection property="students" ofType="com.stumybatis.pojo.Student" >
            <id property="s_id" column="s_id"/>
            <result property="s_name" column="s_name"/>
            <result property="sex" column="sex"/>
            <result property="age" column="age"/>
        </collection>
    </resultMap>
</mapper>

GradeDao介面的內容

public interface GradeDao {

    public Grade selectGradeById(Integer c_id);
}

測試程式碼

@RunWith(SpringJUnit4ClassRunner.class)
@ContextConfiguration({"classpath:spring-mybatis.xml"})
public class StudentDaoTest {

    @Autowired
    private GradeDao gradeDao;

    @Test
    public void testSelecGrade2() throws Exception{
        Grade grade = gradeDao.selectGradeById(1);
        System.out.println(grade.getC_id()+ " "+grade.getCode()+" "+grade.getName());
        List<Student> list = grade.getStudents();
        for(Student student:list){
            System.out.println(student);
        }
    }

結果如下：

但是有一個特別好玩的就是，如果這兩個地方的name不區分的話，那就會有很有意思的結果，就是所有的s_name都寫成name，會出現下圖的結果。把學生的name全都變成了軟體工程。很神奇有沒有。

這裡的環境是搭建好的SSM環境測試的。