多对多：
多对多映射
对于在mybatis中的多对多的处理,其实我们可以参照一对多来解决
【注意】在这个例子中有三个字段都是一样的:id,这种情况一定要小心,
要给列起别名的(上面的一对一和一对多中如果出现这种情况也是一样的处理方式)
建表语句:
drop table course;
drop table student;
drop table student_course;
如果需要可以使用 cascade constraints;
create table course (
id number primary key,
course_code varchar2(30) not null,
course_name varchar2(30) not null
);
create table student (
id number primary key,
name varchar2(10) not null,
gender varchar2(10) ,
major varchar2(10) ,
grade varchar2(10)
);
create table student_course (
id number primary key,
student_id number references student(id),
course_id number references course(id)
);
java代码:
public class Course {
private Integer id;
private String courseCode; // 课程编号
private String courseName;// 课程名称
private List students;// 选课学生
get/set
}
public class Student {
private Integer id;
private String name; // 姓名
private String gender; // 性别
private String major; // 专业
private String grade; // 年级
private List courses;// 所选的课程
get/set
}
Many2ManyMapper.java:
public interface Many2ManyMapper {
//插入student数据
public void insertStudent(Student student);
//插入course数据
public void insertCourse(Course course);
//通过id查询学生
public Student getStudentById(Integer id);
//通过id查询课程
public Course getCourseById(Integer id);
//学生x选课y
public void studentSelectCourse(Student student, Course course);
//查询比指定id值小的学生信息
public List getStudentByIdOnCondition(Integer id);
//查询student级联查询出所选的course并且组装成完整的对象
public Student getStudentByIdWithCourses(Integer id);
}
Many2ManyMapper.xml:
select my_seq.nextval from dual
insert into
student(id,name,gender,major,grade)
values
(#{id},#{name},#{gender},#{major},#{grade})
select my_seq.nextval from dual
insert into
course(id,course_code,course_name)
values
(#{id},#{courseCode},#{courseName})
insert into
student_course(id,student_id,course_id)
values
(my_seq.nextval,#{param1.id},#{param2.id})
测试代码:
@Test
public void test_insertStudent(){
SqlSession session = null;
try {
session = MyBatisSqlSessionFactory.openSession();
Many2ManyMapper mapper = session.getMapper(Many2ManyMapper.class);
mapper.insertStudent(new Student("张三","男","计算机","大四"));
session.commit();
} catch (Exception e) {
e.printStackTrace();
session.rollback();
}finally {
if(session!=null)session.close();
}
}
@Test
public void test_insertCourse(){
SqlSession session = null;
try {
session = MyBatisSqlSessionFactory.openSession();
Many2ManyMapper mapper = session.getMapper(Many2ManyMapper.class);
mapper.insertCourse(new Course("001","corejava"));
mapper.insertCourse(new Course("002","oracle"));
session.commit();
} catch (Exception e) {
e.printStackTrace();
session.rollback();
}finally {
if(session!=null)session.close();
}
}
@Test
public void test_studentSelectCourse(){
SqlSession session = null;
try {
session = MyBatisSqlSessionFactory.openSession();
Many2ManyMapper mapper = session.getMapper(Many2ManyMapper.class);
Student student = mapper.getStudentById(58);
Course course = mapper.getCourseById(59);
mapper.studentSelectCourse(student, course);
session.commit();
} catch (Exception e) {
e.printStackTrace();
session.rollback();
}finally {
if(session!=null)session.close();
}
}
@Test
public void test_getStudentByIdOnCondition(){
SqlSession session = null;
try {
session = MyBatisSqlSessionFactory.openSession();
Many2ManyMapper mapper = session.getMapper(Many2ManyMapper.class);
List list = mapper.getStudentByIdOnCondition(100);
for(Student s:list){
System.out.println(s);
}
} catch (Exception e) {
e.printStackTrace();
}finally {
if(session!=null)session.close();
}
}
@Test
public void test_getStudentByIdWithCourses(){
SqlSession session = null;
try {
session = MyBatisSqlSessionFactory.openSession();
Many2ManyMapper mapper = session.getMapper(Many2ManyMapper.class);
Student student = mapper.getStudentByIdWithCourses(58);
System.out.println(student);
} catch (Exception e) {
e.printStackTrace();
}finally {
if(session!=null)session.close();
}
}
注:这是从student这边出发所做的一些操作,从course一边开始操作是一样的,因为俩者的关系是多对多(对称的).
同时不论是一对一还是一对多还是多对多,都不能在mybatis中进行级联保存、更新、删除,我们需要使用sql语句控制每一步操作