Mybatis -- 複雜查詢環境搭建,多對一的處理,一對多的處理、按結果巢狀查詢(推薦)、按照查詢巢狀處理
阿新 • • 發佈:2021-02-03
文章目錄
一. 複雜查詢環境搭建
具體情況:
多個學生,對應一個老師
- 對於學生這邊而言, 關聯 ,多個學生,關聯一個老師 【多對一】
- 對於老師而言, 集合 , 一個老師,有很多學生 【一對多】
工程目錄如下:
1) 搭建資料表 Teacher、Student
-
Teacher 資料表包含兩個欄位 id、name
-
Student 資料表包含三個欄位 id、name、tid
2) 匯入lombok
在 Maven 工程 pom.xml 匯入 LomBok.jar包
<!--LOG4J-->
<dependency>
<groupId>log4j</groupId>
<artifactId>log4j</artifactId>
<version>1.2.17</version>
</dependency >
3) 新建實體類 Teacher,Student
使用註解形式建立實體類 Teacher,Student
- Teacher 實體類
@Data
public class Teacher {
private int id;
private String name;
}
- Student 實體類
@Data
public class Student {
private int id;
private String name;
// 多個學生關聯一個老師
private Teacher teacher;
}
4) 建立Mapper介面
- TeacherMapper
public interface TeacherMapper {
// 根據id號查詢
@Select("select * from teacher where id = #{tid}")
Teacher getTeacher(@Param("tid") int id);
}
- StudentMapper
public interface StudentMapper {
}
5) 建立Mapper.XML檔案
建立 TeacherMapper.xml 和 StudentMapper.xml 配置檔案
- TeacherMapper.xml
<?xml version="1.0" encoding="UTF8" ?>
<!DOCTYPE mapper
PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN"
"http://mybatis.org/dtd/mybatis-3-mapper.dtd">
<mapper namespace="com.dao.TeacherMapper">
</mapper>
- StudentMapper.xml
<?xml version="1.0" encoding="UTF8" ?>
<!DOCTYPE mapper
PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN"
"http://mybatis.org/dtd/mybatis-3-mapper.dtd">
<mapper namespace="com.dao.StudentMapper">
</mapper>
6) 在核心配置檔案中繫結註冊我們的Mapper介面或者檔案
在 mybatis-config 配置檔案中:
<mappers>
<mapper class="com.dao.TeacherMapper"></mapper>
<mapper class="com.dao.StudentMapper"></mapper>
</mappers>
7) 測試查詢是否能夠成功
@Test
public void getTeacher(){
//第一步:獲得SqlSession物件
SqlSession sqlSession = MybatisUtils.getSqlSession();
//方式一:getMapper
TeacherMapper teacherMapper = sqlSession.getMapper(TeacherMapper.class);
Teacher teacher = teacherMapper.getTeacher(1);
System.out.println(teacher);
//關閉SqlSession
sqlSession.close();
}
二. 多對一的處理 – (學生對老師)
1) Teacher、Student 實體類
- Teacher 實體類
@Data
public class Teacher {
private int id;
private String name;
}
- Student 實體類
@Data
public class Student {
private int id;
private String name;
// 多個學生關聯一個老師
private Teacher teacher;
}
2)TeacherMapper、StudentMapper 介面
- TeacherMapper
public interface TeacherMapper {
// 根據id號查詢
@Select("select * from teacher where id = #{tid}")
Teacher getTeacher(@Param("tid") int id);
}
- StudentMapper
public interface StudentMapper {
// 多對一
// 方式一
public List<Student> getStudent1();
// 方式二
public List<Student> getStudent2();
}
3) TeacherMapper.xml、StudentMapper.xml 配置檔案 (按結果巢狀查詢(推薦)、按照查詢巢狀處理)
- TeacherMapper.xml
<?xml version="1.0" encoding="UTF8" ?>
<!DOCTYPE mapper
PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN"
"http://mybatis.org/dtd/mybatis-3-mapper.dtd">
<mapper namespace="com.dao.TeacherMapper">
</mapper>
- StudentMapper.xml
<?xml version="1.0" encoding="UTF8" ?>
<!DOCTYPE mapper
PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN"
"http://mybatis.org/dtd/mybatis-3-mapper.dtd">
<mapper namespace="com.dao.StudentMapper">
<!-- 多對一 -->
<!-- 方式一(子查詢)按照查詢巢狀處理 -->
<select id="getStudent1" resultMap="StudentTeacher1">
select * from student
</select>
<resultMap id="StudentTeacher1" type="Student"><!-- resultmap -->
<result property="id" column="id"/>
<result property="name" column="name"/>
<!--複雜的屬性,我們需要單獨處理 物件: association 集合: collection -->
<association property="teacher" column="tid" javaType="Teacher" select="getTeacher"/>
</resultMap>
<select id="getTeacher" resultType="Teacher">
select * from teacher where id = #{id}
</select>
<!-- 方式二(連表查詢)按照結果巢狀處理 -->
<select id="getStudent2" resultMap="StudentTeacher2">
select s.id sid, s.name sname, t.id tid, t.name tname
from student s,teacher t
where s.tid = t.id;
</select>
<resultMap id="StudentTeacher2" type="Student">
<result property="id" column="sid"/>
<result property="name" column="sname"/>
<association property="teacher" javaType="Teacher">
<result property="id" column="tid"/>
<result property="name" column="tname"/>
</association>
</resultMap>
</mapper>
4) 測試
public class My_Test {
@Test
public void getTeacher(){
//第一步:獲得SqlSession物件
SqlSession sqlSession = MybatisUtils.getSqlSession();
//方式一:getMapper
TeacherMapper teacherMapper = sqlSession.getMapper(TeacherMapper.class);
Teacher teacher = teacherMapper.getTeacher(1);
System.out.println(teacher);
//關閉SqlSession
sqlSession.close();
}
@Test
public void getStudent1(){
//第一步:獲得SqlSession物件
SqlSession sqlSession = MybatisUtils.getSqlSession();
//方式一:getMapper
StudentMapper studentMapper = sqlSession.getMapper(StudentMapper.class);
List<Student> list = studentMapper.getStudent1();
for(Student student:list){
System.out.println(student);
}
//關閉SqlSession
sqlSession.close();
}
@Test
public void getStudent2(){
//第一步:獲得SqlSession物件
SqlSession sqlSession = MybatisUtils.getSqlSession();
//方式一:getMapper
StudentMapper studentMapper = sqlSession.getMapper(StudentMapper.class);
List<Student> list = studentMapper.getStudent2();
for(Student student:list){
System.out.println(student);
}
//關閉SqlSession
sqlSession.close();
}
}
三. 一對多的處理 – (老師對學生)
1) Teacher、Student 實體類
- Teacher 實體類
@Data
public class Teacher {
private int id;
private String name;
private List<Student> students;
}
- Student 實體類
@Data
public class Student {
private int id;
private String name;
private String tid;
}
2)TeacherMapper、StudentMapper 介面
- TeacherMapper 介面
public interface TeacherMapper {
List<Teacher> getTeacher();
Teacher getTeacher1(int id);
Teacher getTeacher2(int id);
}
- StudentMapper 介面
public interface StudentMapper {
}
3) TeacherMapper.xml、StudentMapper.xml 配置檔案 (按結果巢狀查詢(推薦)、按照查詢巢狀處理)
- TeacherMapper.xml
<?xml version="1.0" encoding="UTF8" ?>
<!DOCTYPE mapper
PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN"
"http://mybatis.org/dtd/mybatis-3-mapper.dtd">
<mapper namespace="com.dao.TeacherMapper">
<!-- 測試程式碼1 -->
<select id="getTeacher" resultType="Teacher">
select * from teacher
</select>
<!--按結果巢狀查詢-->
<select id="getTeacher1" resultMap="TeacherStudent">
select s.id sid, s.name sname, t.name tname,t.id tid
from student s,teacher t
where s.tid = t.id and t.id = #{tid}
</select>
<resultMap id="TeacherStudent" type="Teacher">
<result property="id" column="tid"/>
<result property="name" column="tname"/>
<!--複雜的屬性,我們需要單獨處理 物件: association 集合: collection
javaType="" 指定屬性的型別!
集合中的泛型資訊,我們使用ofType獲取
-->
<collection property="students" ofType="Student">
<result property="id" column="sid"/>
<result property="name" column="sname"/>
<result property="tid" column="tid"/>
</collection>
</resultMap>
<!-- 按照查詢巢狀處理 -->
<select id="getTeacher2" resultMap="TeacherStudent2">
select * from mybatis.teacher where id = #{tid}
</select>
<resultMap id="TeacherStudent2" type="Teacher">
<collection property="students" javaType="ArrayList" ofType="Student" select="getStudentByTeacherId" column="id"/>
</resultMap>
<select id="getStudentByTeacherId" resultType="Student">
select * from mybatis.student where tid = #{tid}
</select>
</mapper>
- StudentMapper.xml
<?xml version="1.0" encoding="UTF8" ?>
<!DOCTYPE mapper
PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN"
"http://mybatis.org/dtd/mybatis-3-mapper.dtd">
<mapper namespace="com.dao.StudentMapper">
</mapper>
4) 測試
public class My_Test
{
@Test
public void getTeacher(){
SqlSession sqlSession = MybatisUtils.getSqlSession();
//方式一:getMapper
TeacherMapper mapper = sqlSession.getMapper(TeacherMapper.class);
List<Teacher> teachers = mapper.getTeacher();
for(Teacher teacher: teachers){
System.out.println(teacher);
}
//關閉SqlSession
sqlSession.close();
}
@Test
public void getTeacher1(){
//第一步:獲得SqlSession物件
SqlSession sqlSession = MybatisUtils.getSqlSession();
//方式一:getMapper
TeacherMapper mapper = sqlSession.getMapper(TeacherMapper.class);
Teacher teacher = mapper.getTeacher1(1);
System.out.println(teacher);
//關閉SqlSession
sqlSession.close();
}
@Test
public void getTeacher2(){
//第一步:獲得SqlSession物件
SqlSession sqlSession = MybatisUtils.getSqlSession();
//方式一:getMapper
TeacherMapper mapper = sqlSession.getMapper(TeacherMapper.class);
Teacher teacher = mapper.getTeacher2(1);
System.out.println(teacher);
//關閉SqlSession
sqlSession.close();
}
}