3.3 结果集映射 ResultMaps
ResultMaps被用来将SELECT语句的结果集映射到java对象的属性中。我们可以定义结果集映射ResultMaps并且在一些SELECT语句上引用resultMap。MyBatis的结果集映射 ResultMaps特性非常强大，你可以使用它将简单的SELECT语句映射到复杂的一对一、一对多关系的SELECT语句上。
3.3.1 简单ResultMap
一个映射了查询结果为Student类型的resultMap定义如下：
<resultMap id="StudentResult" type="com.briup.pojo.Student">
<id property="studId" column="stud_id" />
<result property="name" column="name" />
<result property="email" column="email" />
<result property="phone" column="phone" />
</resultMap>
resultMap的id值应该在此名空间内是唯一的,并且type属性是完全限定类名或者是返回类型的别名。
<result>子元素被用来将一个resultset列映射到对象的一个属性中。
<id>元素和<result>元素功能相同，不过<id>它被用来映射到唯一标识属性，用来区分和比较对象（一般和主键列相对应）。
在<select>语句中，我们使用了resultMap属性，而不是resultType属性。当<select>语句中配置了resutlMap属性，MyBatis会使用表中的列名与对象属性 【映射关系】 来填充对象中的属性值。
注意:resultType和resultMap二者只能用其一，不能同时使用。
实例1：
<select id="findAllStudents" resultMap="StudentResult">
SELECT * FROM STUDENTS
</select>
实例2：
<select id="findStudentById" parameterType="int"
resultMap="StudentResult">
SELECT * FROM STUDENTS WHERE STUD_ID=#{studId}
</select>
实例3:
<select id="findAllStudents_student" resultType="Student">
SELECT STUD_ID AS STUDID,NAME,EMAIL,DOB
FROM STUDENTS
</select>
对应的接口中的方法,你写什么类型的集合,Mybatis就给你返回什么类型的集合,但是要注意使用SortedSet的时候,Student类需要实现Comparable接口,否则是不能进行排序的
例如:
public List<Student> findAllStudents_List();
或者
public Set<Student> findAllStudents_Set();
或者
public SortedSet<Student> findAllStudents_SortedSet();
实例4:
<select id="findAllName_list" resultType="String">
SELECT NAME
FROM STUDENTS
</select>
对应的接口中的方法: 把查询到所有名字都放到List集合中并返回
public List<String> findAllName_list();
实例5:
<select id="findCount_int" resultType="int">
SELECT count(*)
FROM STUDENTS
</select>
对应的接口中的方法: 把查询到的这个值直接返回
public int findCount_int();
实例6：
<select>映射语句中如何将查询【一条】数据填充到Map中?
<select id="findStudentById" parameterType="int" resultType="map">
SELECT * FROM STUDENTS WHERE STUD_ID=#{studId}
</select>
在上述的<select>语句中，我们将resultType配置成map，即java.util.HashMap的别名。在这种情况下，
结果集的列名将会作为Map中的key值，而列值将作为Map的value值。
HashMap<String,Object> studentMap = sqlSession.selectOne("com.briup.mappers.StudentMapper.findStudentById", studId);
System.out.println("stud_id :"+studentMap.get("stud_id"));
System.out.println("name :"+studentMap.get("name"));
System.out.println("email :"+studentMap.get("email"));
System.out.println("phone :"+studentMap.get("phone"));
实例7：
<select>映射语句中如何将查询【多条】数据填充到Map中?
<select id="findAllStudents" resultType="map">
SELECT STUD_ID, NAME, EMAIL, PHONE FROM STUDENTS
</select>
由于resultType=”map”和语句返回多行，则最终返回的数据类型应该是List<Map<String,Object>>，如下所示：
List<Map<String, Object>> studentMapList = sqlSession.select List("com.briup.mappers.StudentMapper.findAllStudents");
for(Map<String, Object> studentMap : studentMapList) {
System.out.println("studId :" + studentMap.get("stud_id"));
System.out.println("name :" + studentMap.get("name"));
System.out.println("email :" + studentMap.get("email"));
System.out.println("phone :" + studentMap.get("phone"));
}
3.3.2 拓展 ResultMap
(注:这个例子在下面的一对一映射的知识点中进行测试,因为这里需要建立一对一关系的表结构)
我们可以从从另外一个<resultMap>，拓展出一个新的<resultMap>，这样，原先的属性映射可以继承过来，以实现:
<resultMap type="Student" id="StudentResult">
<id property="studId" column="stud_id" />
<result property="name" column="name" />
<result property="email" column="email" />
<result property="phone" column="phone" />
</resultMap>
<!-- Student类中又新增加了一个属性,该属性的类型是Address -->
<!-- 自定义类Address,类中也有多个属性,同时数据库中ADDRESSES表与其对应 -->
<resultMap type="Student" id="StudentWithAddressResult"
extends="StudentResult">
<result property="address.addrId" column="addr_id" />
<result property="address.street" column="street" />
<result property="address.city" column="city" />
<result property="address.state" column="state" />
<result property="address.zip" column="zip" />
<result property="address.country" column="country" />
</resultMap>
其中id为StudentWithAddressResult的resultMap拓展了id为StudentResult的resultMap
如果你只想映射Student数据，你可以使用id为StudentResult的resultMap,如下所示：
<select id="findStudentById" parameterType="int"
resultMap="StudentResult">
SELECT * FROM STUDENTS WHERE STUD_ID=#{stud Id}
</select>
如果你想将映射Student数据和Address数据，你可以使用id为StudentWithAddressResult的 resultMap：
<select id="selectStudentWithAddress" parameterType="int"
resultMap="StudentWithAddressResult">
SELECT STUD_ID, NAME, EMAIL, PHONE, A.ADDR_ID, STREET, CITY, STATE, ZIP, COUNTRY
FROM STUDENTS S LEFT OUTER JOIN ADDRESSES A ON
S.ADDR_ID=A.ADDR_ID
WHERE STUD_ID=#{studId}
</select>
注:该sql语句使用了连接查询中的左外连接,也可以使用等值连接
3.4 一对一映射
Student和Address是一个【一对一】关系
建表语言:
drop table students;
drop table addresses cascade constraints;
如果需要可以使用 cascade constraints;
create table addresses(
addr_id number primary key,
street varchar2(50) not null,
city varchar2(50) not null,
state varchar2(50) not null,
zip varchar2(10),
country varchar2(50)
);
create table students(
stud_id number primary key,
name varchar2(50) not null,
email varchar2(50),
phone varchar2(15),
dob date ,
addr_id number references addresses(addr_id)
);
java类:
public class PhoneNumber {
private String countryCode;
private String stateCode;
private String number;
get/set
}
public class Address{
private Integer addrId;
private String street;
private String city;
private String state;
private String zip;
private String country;
get/set
}
public class Student {
private Integer studId;
private String name;
private String email;
private Date dob;
private PhoneNumber phone;
private Address address;
get/set
}
addresses 表的样例输入如下所示：
addr_id street
city
state
zip country
1
redSt
kunshan W
12345 china
2
blueST
kunshan W
12345 china
insert into addresses(addr_id,street,city,state,zip,country) values(1,'redSt','kunshan','W','12345','china');
insert into addresses(addr_id,street,city,state,zip,country) values(2,'blueST','kunshan','W','12345','china');
commit;
students 表的样例数据如下所示：
stud_id name email
phone
addr_id
1 John john@gmail.com 123-456-7890 1
2 Paul paul@gmail.com 111-222-3333 2
insert into students(stud_id,name,email,phone,addr_id) values(1,'John','john@gmail.com','123-456-7890',1);
insert into students(stud_id,name,email,phone,addr_id) values(2,'Paul','paul@gmail.com','111-222-3333',2);
commit;
mapper XML:
<resultMap type="Student" id="StudentWithAddressResult">
<id property="studId" column="stud_id" />
<result property="name" column="name" />
<result property="email" column="email" />
<result property="phone" column="phone" />
<result property="address.addrId" column="addr_id" />
<result property="address.street" column="street" />
<result property="address.city" column="city" />
<result property="address.state" column="state" />
<result property="address.zip" column="zip" />
<result property="address.country" column="country" />
</resultMap>
<select id="selectStudentWithAddress" parameterType="int" resultMap="StudentWithAddressResult">
select stud_id, name, email,phone, a.addr_id, street, city, state, zip, country
from students s left outer join addresses a on
s.addr_id=a.addr_id
where stud_id=#{studid}
</select>
我们可以使用(对象.属性名)的方式为内嵌的对象的属性赋值。在上述的resultMap中，Student的address属性使用该方式被赋上了 address 对应列的值。同样地，我们可以访问【任意深度】的内嵌对象的属性。
//接口定义
public interface Student Mapper{
Student selectStudentWithAddress(int studId);
}
//方法调用
int studId = 1;
StudentMapper studentMapper = sqlSession.getMapper(StudentMapper.class);
Student student = studentMapper.selectStudentWithAddress(studId);
System.out.println("Student :" + student);
System.out.println("Address :" + student.getAddress());
练习：写一个插入一条数据的例子，先插入地址对象，再插入学生对象。
上面展示了一对一关联映射的一种方法。然而，使用这种方式映射，如果address结果需要在其他的SELECT映射语句中映射成Address对象，我们需要为每一个语句重复这种映射关系。MyBatis提供了更好地实现一对一关联映射的方法：【嵌套结果】ResultMap和【嵌套查询】select语句。接下来，我们将讨论这两种方式。
3.4.1 使用嵌套结果ResultMap实现一对一关系映射
我们可以使用一个嵌套结果ResultMap方式来获取Student及其Address信息，这个方式可以反复利用。代码如下：
<resultMap type="Address" id="AddressResult">
<id property="addrId" column="addr_id" />
<result property="street" column="street" />
<result property="city" column="city" />
<result property="state" column="state" />
<result property="zip" column="zip" />
<result property="country" column="country" />
</resultMap>
<resultMap type="Student" id="StudentWithAddressResult">
<id property="studId" column="stud_id" />
<result property="name" column="name" />
<result property="email" column="email" />
<association property="address" resultMap="AddressResult" />
</resultMap>
<select id="findStudentWithAddress" parameterType="int" resultMap="StudentWithAddressResult">
select stud_id, name, email, a.addr_id, street, city, state,
zip, country
from students s left outer join addresses a on
s.addr_id=a.addr_id
where stud_id=#{studid}
</select>
注:association是关联的意思
元素<association>被用来导入“有一个”(has-one)类型的关联。在上述的例子中，我们使用了<association>元素引用了另外的在同一个XML文件中定义的<resultMap>。
同时我们也可以使用<association> 定义内联的resultMap，代码如下所示：
<resultMap type="Student" id="StudentWithAddressResult">
<id property="studId" column="stud_id" />
<result property="name" column="name" />
<result property="email" column="email" />
<association property="address" javaType="Address">
<id property="addrId" column="addr_id" />
<result property="street" column="street" />
<result property="city" column="city" />
<result property="state" column="state" />
<result property="zip" column="zip" />
<result property="country" column="country" />
</association>
</resultMap>
3.4.2 使用嵌套查询select实现一对一关系映射
我们可以通过使用嵌套select查询来获取Student及其Address信息，代码如下：
<resultMap id="AddressResult" type="Address">
<id property="addrId" column="addr_id" />
<result property="street" column="street" />
<result property="city" column="city" />
<result property="state" column="state" />
<result property="zip" column="zip" />
<result property="country" column="country" />
</resultMap>
<select id="findAddressById" parameterType="int" resultMap="AddressResult">
select * from addresses where addr_id=#{id}
</select>
<resultMap id="StudentWithAddressResult" type="Student">
<id property="studId" column="stud_id" />
<result property="name" column="name" />
<result property="email" column="email" />
<association property="address" column="addr_id" select="findAddressById" />
</resultMap>
<select id="findStudentWithAddress" parameterType="int" resultMap="StudentWithAddressResult">
select * from students where stud_id=#{id}
</select>
在此方式中，<association>元素的select属性被设置成了id为findAddressById的语句。这里，两个分开的SQL语句将会在数据库中分别执行，第一个调用findStudentById加载student信息，而第二个调用findAddressById来加载address信息。
addr_id列的值将会被作为输入参数传递给selectAddressById语句。
我们可以如下调用findStudentWithAddress映射语句：
StudentMapper mapper = sqlSession.getMapper(StudentMapper.class);
Student student = mapper.selectStudentWithAddress(studId);
System.out.println(student);
System.out.println(student.getAddress());
3.5 一对多映射
一个讲师tutors可以教一个或者多个课程course。这意味着讲师和课程之间存在一对多的映射关系。
注意:在一对多关系中,数据库建表的时候外键一定是在多的那一方建立.
建表语句:
drop table tutors cascade constraints;
drop table courses cascade constraints;
如果需要可以使用 cascade constraints;
create table tutors(
tutor_id number primary key,
name varchar2(50) not null,
email varchar2(50) ,
phone varchar2(15) ,
addr_id number(11) references addresses (addr_id)
);
create table courses(
course_id number primary key,
name varchar2(100) not null,
description varchar2(512),
start_date date ,
end_date date ,
tutor_id number references tutors (tutor_id)
);
tutors 表的样例数据如下：
tutor_id name email
phone
addr_id
1
zs zs@briup.com 123-456-7890 1
2
ls ls@briup.com 111-222-3333 2
insert into tutors(tutor_id,name,email,phone,addr_id)
values(1,'zs','zs@briup.com','123-456-7890',1);
insert into tutors(tutor_id,name,email,phone,addr_id)
values(2,'ls','ls@briup.com','111-222-3333',2);
commit;
course 表的样例数据如下：
course_id name description start_date end_date tutor_id
1
JavaSE JavaSE 2015-09-10 2016-02-10 1
2
JavaEE JavaEE 2015-09-10 2016-03-10 2
3
MyBatis MyBatis 2015-09-10 2016-02-20 2
insert into
courses(course_id,name,description,start_date,end_date,tutor_id)
values(1,'JavaSE','JavaSE',to_date('2015-09-10','yyyy-mm-dd'),to_date('2016-02-10','yyyy-mm-dd'),1);
insert into
courses(course_id,name,description,start_date,end_date,tutor_id)
values(2,'JavaEE','JavaEE',to_date('2015-09-10','yyyy-mm-dd'),to_date('2016-03-10','yyyy-mm-dd'),2);
insert into
courses(course_id,name,description,start_date,end_date,tutor_id)
values(3,'MyBatis','MyBatis',to_date('2015-09-10','yyyy-mm-dd'),to_date('2016-02-20','yyyy-mm-dd'),1);
commit;
在上述的表数据中，zs讲师教授一个课程，而ls讲师教授两个课程
java代码:
public class Tutor{
private Integer tutorId;
private String name;
private String email;
private PhoneNumber phone;
private Address address;
private List<Course> courses;
get/set
}
public class Course{
private Integer courseId;
private String name;
private String description;
private Date startDate;
private Date endDate;
get/set
}
<collection>元素被用来将多行课程结果映射成一个课程Course对象的一个集合。和一对一映射一样，我们可以使用【嵌套结果ResultMap】和【嵌套查询Select】语句两种方式映射实现一对多映射。
3.5.1 使用内嵌结果 ResultMap 实现一对多映射
我们可以使用嵌套结果resultMap方式获得讲师及其课程信息，代码如下：
<resultMap type="Address" id="AddressResult">
<id property="addrId" column="addr_id" />
<result property="street" column="street" />
<result property="city" column="city" />
<result property="state" column="state" />
<result property="zip" column="zip" />
<result property="country" column="country" />
</resultMap>
<resultMap type="Course" id="CourseResult">
<id column="course_id" property="courseId" />
<result column="name" property="name" />
<result column="description" property="description" />
<result column="start_date" property="startDate" />
<result column="end_date" property="endDate" />
</resultMap>
<resultMap type="Tutor" id="TutorResult">
<id column="tutor_id" property="tutorId" />
<result column="name" property="name" />
<result column="email" property="email" />
<result column="phone" property="phone" />
<association property="address" resultMap="AddressResult" />
<collection property="courses" resultMap="CourseResult" />
</resultMap>
<select id="findTutorById" parameterType="int" resultMap="TutorResult">
select t.tutor_id, t.name, t.email, c.course_id, c.name, description, start_date, end_date
from tutors t left outer join addresses a on t.addr_id=a.addr_id
left outer join courses c on t.tutor_id=c.tutor_id
where t.tutor_id=#{tutorid}
</select>
这里我们使用了一个简单的使用了JOINS连接的Select语句获取讲师及其所教课程信息。<collection>元素的resultMap属性设置成了CourseResult，CourseResult包含了Course对象属性与表列名之间的映射。
如果同时也要查询到Address相关信息,可以按照上面一对一的方式,在配置中加入<association>即可
3.5.2 使用嵌套Select语句实现一对多映射
我们可以使用嵌套Select语句方式获得讲师及其课程信息，代码如下：
<resultMap type="Address" id="AddressResult">
<id property="addrId" column="addr_id" />
<result property="street" column="street" />
<result property="city" column="city" />
<result property="state" column="state" />
<result property="zip" column="zip" />
<result property="country" column="country" />
</resultMap>
<resultMap type="Course" id="CourseResult">
<id column="course_id" property="courseId" />
<result column="name" property="name" />
<result column="description" property="description" />
<result column="start_date" property="startDate" />
<result column="end_date" property="endDate" />
</resultMap>
<resultMap type="Tutor" id="TutorResult">
<id column="tutor_id" property="tutorId" />
<result column="tutor_name" property="name" />
<result column="email" property="email" />
<association property="address" column="addr_id" select="findAddressById"></association>
<!-- 这里要注意:是把当前tutor_id表中列的值当做参数去执行findCoursesByTutor这个查询语句,最后把查询结果封装到Tutor类中的courses属性中 -->
<collection property="courses" column="tutor_id" select="findCoursesByTutor" />
</resultMap>
<select id="findTutorById" parameterType="int" resultMap="TutorResult">
select *
from tutors
where tutor_id=#{tutor_id}
</select>
<select id="findAddressById" parameterType="int" resultMap="AddressResult">
select *
from addresses
where addr_id = #{addr_id}
</select>
<select id="findCoursesByTutor" parameterType="int" resultMap="CourseResult">
select *
from courses
where tutor_id=#{tutor_id}
</select>
在这种方式中，<aossication>元素的select属性被设置为id为findCourseByTutor的语句，用来触发单独的SQL查询加载课程信息。tutor_id这一列值将会作为输入参数传递给 findCouresByTutor语句。
mapper接口代码:
public interface TutorMapper{
Tutor findTutorById(int tutorId);
}
//方法调用
TutorMapper mapper = sqlSession.getMapper(TutorMapper.class);
Tutor tutor = mapper.findTutorById(tutor Id);
System.out.println(tutor);
List<Course> courses = tutor.getCourses();
for (Course course : courses){
System.out.println(course);
}
【注意】嵌套查询Select语句查询会导致1+N选择问题。首先，主查询将会执行（1 次），对于主查询返回的每一行，另外一个查询将会被执行（主查询 N 行，则此查询 N 次）。对于大量数据而言，这会导致很差的性能问题。
3.5 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 student_course;
drop table course;
drop table student;
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)
);
表中的样例例子：
insert into course values(1,'101','CoreJava');
insert into course values(2,'102','Oracle');
insert into Student values(1,'tom','男','计算机','大四');
insert into Student values(2,'jack','男','计算机','大四');
insert into student_course values(1,1,1);
insert into student_course values(2,1,2);
insert into student_course values(3,2,1);
insert into student_course values(4,2,2);
commit;
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<Student> 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<Course> 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<Student> 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:
<insert id="insertStudent" parameterType="Student">
<selectKey keyProperty="id" resultType="int" order="BEFORE">
select my_seq.nextval from dual
</selectKey>
insert into
student(id,name,gender,major,grade)
values
(#{id},#{name},#{gender},#{major},#{grade})
</insert>
<insert id="insertCourse" parameterType="Course">
<selectKey keyProperty="id" resultType="int" order="BEFORE">
select my_seq.nextval from dual
</selectKey>
insert into
course(id,course_code,course_name)
values
(#{id},#{courseCode},#{courseName})
</insert>
<select id="getStudentById" parameterType="int" resultType="Student">
select id,name,gender,major,grade
from student
where id=#{id}
</select>
<select id="getCourseById" parameterType="int" resultType="Course">
select id,course_code as courseCode,course_name as courseName
from course
where id=#{id}
</select>
<!-- param1代表方法中第一个参数 以此类推 -->
<insert id="studentSelectCourse">
insert into
student_course(id,student_id,course_id)
values
(my_seq.nextval,#{param1.id},#{param2.id})
</insert>
<!-- 如果有特殊符号的话 需要用 <![CDATA[ 特殊符号 ]]> 例如 < & 等等 -->
<select id="getStudentByIdOnCondition" parameterType="int" resultType="Student">
select *
from student
where id <![CDATA[ < ]]> #{id}
</select>
<!--
这里使用了嵌套结果ResultMap的方式进行级联查询
当然也可以使用嵌套查询select
-->
<!-- 映射一个基本的Student查询结果 -->
<resultMap id="StudentResult" type="Student">
<id property="id" column="id"/>
<result property="name" column="name"/>
<result property="gender" column="gender"/>
<result property="major" column="major"/>
<result property="grade" column="grade"/>
</resultMap>
<!-- 继承上面那个基本的映射,再扩展出级联查询 -->
<resultMap id="StudentResultWithCourses" type="Student" extends="StudentResult">
<collection property="courses" resultMap="CourseResult"></collection>
</resultMap>
<!-- 这里特别要是的是column="cid" 这是和select语句中的 c.id as cid对应的 一定一定一定要对应起来 -->
<resultMap id="CourseResult" type="Course">
<id property="id" column="cid"/>
<result property="courseCode" column="course_code"/>
<result property="courseName" column="course_name"/>
</resultMap>
<!--
注意:查询语句的中的c.id as cid这个地方,避免名字相同出现查询结果不正确的情况
同时在id="CourseResult"的resultMap中也有与这里对应的设置要特别特别注意
-->
<select id="getStudentByIdWithCourses" parameterType="int" resultMap="StudentResultWithCourses">
select s.id,s.name,s.gender,s.major,s.grade,c.id as cid,c.course_code,c.course_name,sc.id,sc.student_id,sc.course_id
from student s,course c,student_course sc
where
s.id=#{id}
and
s.id=sc.student_id
and
sc.course_id=c.id
</select>
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<Student> 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
resultmap标签可以有多个
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