当前位置：网站首页>Mybaits之多表查询（联合查询、嵌套查询）
Mybaits之多表查询（联合查询、嵌套查询）
2022-07-06 23:34:00 【PIKapikaaaa】
多表联合查询
(一) 多表联合查询概述
在开发过程中单表查询不能满足项目需求分析功能，对于复杂业务来讲，关联的表有几张，甚至几十张并且表与表之间的关系相当复杂。为了能够实业复杂功能业务，就必须进行多表查询，在mybatis中提供了多表查询的结果时映射标签，可以实现表之间的一对一、一对多、多对一、多对多关系映射。
(二) MyBatis多表查询之一对一
1. 构建数据库表:person(个人表) IdCard(身份证表)
#person表 CREATE TABLE person( p_id INT NOT NULL AUTO_INCREMENT, p_name VARCHAR(30), PRIMARY KEY(p_id) ); #IdCard表 CREATE TABLE idcard( c_id INT NOT NULL AUTO_INCREMENT, c_cardno VARCHAR(18), c_uselife DATE, c_person_id INT NOT NULL, PRIMARY KEY(c_id), FOREIGN KEY(c_person_id) REFERENCES person(p_id), UNIQUE KEY(c_cardno), UNIQUE KEY(c_person_id) ); INSERT INTO person(p_name) VALUES('张三'),('李四'); INSERT INTO idcard(c_cardno,c_uselife,c_person_id) VALUES('110112199012127821','2029-10-10',1); INSERT INTO idcard(c_cardno,c_uselife,c_person_id) VALUES('120114199911103491','2030-12-01',2);
2.准备项目环境
1) 构建maven项目，添加依赖
<dependencies> <dependency> <groupId>org.mybatis</groupId> <artifactId>mybatis</artifactId> <version>3.4.6</version> </dependency> <dependency> <groupId>mysql</groupId> <artifactId>mysql-connector-java</artifactId> <version>5.1.47</version> <scope>runtime</scope> </dependency> <dependency> <groupId>junit</groupId> <artifactId>junit</artifactId> <version>4.12</version> <scope>test</scope> </dependency> <dependency> <groupId>log4j</groupId> <artifactId>log4j</artifactId> <version>1.2.17</version> </dependency> </dependencies>
2)编写框架配置文件sqlMapConfig.xml
<?xml version="1.0" encoding="UTF-8"?> <!DOCTYPE configuration PUBLIC "-//mybatis.org//DTD Config 3.0//EN" "http://mybatis.org/dtd/mybatis-3-config.dtd"> <configuration> <!-- 配置 mybatis的环境 --> <environments default="development"> <!-- 配置环境 --> <environment id="development"> <!-- 配置事务的类型 --> <transactionManager type="JDBC"></transactionManager> <!-- 配置连接数据库的信息:用的是数据源【连接池】--> <dataSource type="POOLED"> <property name="driver" value="com.mysql.jdbc.Driver"/> <property name="url" value="jdbc:mysql://localhost:3306/mybatis002"/> <property name="username" value="root"/> <property name="password" value="root"/> </dataSource> </environment> </environments> <mappers> <package name="cn.offcn.dao"></package> </mappers </configuration>
3.方式一：嵌套结果方式
1)创建数据模型Person对象,IdCard对象
public class Person { private Integer id; private String name; private Idcard idcard; } public class Idcard { private Integer id; private String cardno; private Date uselife; }
2)定义持久层接口PersonMapper
public interface PersonDao{ /** * 根据id查询person对象 */ Person getPersonById1(int i); }
3)定义 PersonMapper.xml 文件中的查询配置信息
<resultMap id="BaseResultMap" type="Person"> <id column="p_id" property="id"></id> <result column="p_name" property="name"></result> </resultMap> <resultMap id="PersonResultMap1" type="Person" extends="BaseResultMap"> <association property="idcard" javaType="Idcard"> <id column="c_id" property="id"></id> <result column="c_cardno" property="cardno"></result> <result column="c_uselife" property="uselife"></result> </association> </resultMap> <!-- 根据部门id查找部门 以及所在部门所有员工的所有信息【嵌套结果查询，联合查询】 --> <select id="getPersonById1" parameterType="int" resultType="Person" resultMap="PersonResultMap1"> select p.*,c.* from person p,idcard c where p.p_id=c.c_person_id and p.p_id=#{id} </select>
4)创建 PersonTest 测试类
@Test // 根据人的id查询人与信息 和 身份证信息 【嵌套结果查询，连表查询】 public void getPersonById1(){ SqlSession session = MyBatisUtils.getSession(); PersonMapper mapper = session.getMapper(PersonMapper.class); Person person = mapper.getPersonById1(1); // 输出 System.out.println(person); System.out.println(person.getIdcard().toString()); MyBatisUtils.close(session); }
4.方式二：嵌套查询方式
1)创建数据模型Person对象,IdCard对象
public class Person { private Integer id; private String name; private Idcard idcard; } public class Idcard { private Integer id; private String cardno; private Date uselife; }
2)定义持久层接口PersonMapper
public interface IdCardDao{
/** * 根据c_person_id查询IdCard对象 */
Person getPersonById2(int i);
}
3)定义 PersonMapper.xml 文件中的查询配置信息
<!-- 根据人的id查询人与信息 和 身份证信息 【嵌套查询，分表查询】 --> <select id="getPersonById2" parameterType="int" resultType="Person" resultMap="PersonResultMap2"> select * from person where p_id=#{id} </select> <resultMap id="BaseResultMap" type="Person"> <id column="p_id" property="id"></id> <result column="p_name" property="name"></result> </resultMap> <resultMap id="PersonResultMap2" type="Person" extends="BaseResultMap"> <association property="idcard" javaType="Idcard" column="p_id" select="com.chenshuang.mapper.IdcardMapper.getIdcardById"> </association> </resultMap>
4)定义持久层接口IdcardMapper
public interface IdcardMapper { Idcard getIdcardById(int id); }
5)定义 IdcardMapper.xml 文件中的查询配置信息
<mapper namespace="com.chenshuang.mapper.IdcardMapper"> <resultMap id="BaseResultMap" type="Idcard"> <id column="c_id" property="id"></id> <result column="c_cardno" property="cardno"></result> <result column="c_uselife" property="uselife"></result> </resultMap> <select id="getIdcardById" parameterType="int" resultType="Idcard" resultMap="BaseResultMap"> select * from idcard where c_id=#{id} </select> </mapper>
6)PersonTest 类中加入测试方法
@Test // 根据人的id查询人与信息 和 身份证信息 【嵌套查询，分表查询】 public void getPersonById2(){ SqlSession session = MyBatisUtils.getSession(); PersonMapper mapper = session.getMapper(PersonMapper.class); Person person = mapper.getPersonById2(1); System.out.println(person); System.out.println(person.getIdcard().toString()); MyBatisUtils.close(session); }
(三) MyBatis实现一对多查询
1.创建数据库表:department(部门表),employee(员工表)同时设定部门和员工表的关系
CREATE TABLE department( d_id INT NOT NULL AUTO_INCREMENT, d_name VARCHAR(100), PRIMARY KEY(d_id) ); CREATE TABLE employee( e_id INT NOT NULL AUTO_INCREMENT, e_name VARCHAR(30), e_gender VARCHAR(6), e_age INT, e_depart_id INT, PRIMARY KEY(e_id), FOREIGN KEY(e_depart_id) REFERENCES department(d_id) );
2.方式一:嵌套结果，连表查询的方式
1）创建数据模型department和employee
public class Department { private Integer id; private String name; private List<Employee> employees; } public class Employee { private Integer id; private String name; private String gender; private Integer age; private Department depart; }
2）部门持久层DepartmentMapper 接口中加入查询方法
public interface DepartmentMapper { Department getDepartmentById1(int id); Department getDepartmentById2(int id); }
3）部门持久层 DepartmentMapper.xml 映射文件配置
<?xml version="1.0" encoding="UTF-8" ?> <!DOCTYPE mapper PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN" "http://mybatis.org/dtd/mybatis-3-mapper.dtd"> <mapper namespace="cn.offcn.mapper.DepartmentDao"> <select id="getDepartmentById" resultMap="DepartemntResultMap2"> SELECT d.*,e.* FROM department d, employee e WHERE e.e_depart_id=d.d_id AND d.d_id=#{id} </select> <resultMap id="DepartemntResultMap" type="Department"> <id column="d_id" property="id"></id> <result column="d_name" property="name"></result> <collection property="emps" ofType="Employee"> <id column="e_id" property="id"></id> <result column="e_name" property="name"></result> <result column="e_gender" property="gender"></result> <result column="e_age" property="age"></result> </collection> </resultMap> collection：当属性为集合时，使用collection标签进行映射。
4）测试方法
@Test
public void testGetDepartentById() throws Exception{
//获取SqlSession对象
SqlSession session = MyBatisUtils.getSession();
//调用SqlSession 创建 UserDao接口的代理对象
DepartmentDao departmentDao = session.getMapper(DepartmentDao.class);
Department dept=departmentDao.getDepartentById(1);
//打印
System.out.println(dept);
//提交事务
session.commit();
//关闭连接
MyBatisUtils.close(session);
}
3.方式二:嵌套查询，分表查询的方式
1）定义员工的持久层接口EmployeeMapper
public interface EmployeeDao { public List<Employee> getEmployeeByDepartId(int id); }
2）定义DepartmentMapper.xml 文件中的查询配置信息
<select id="getEmployeeByDepartId" resultType="Employee"> select e_id id,e_name name,e_gender gender,e_age age from employee where e_depart_id=#{ id} </select>
3）定义DepartmentMapper.xml配置文件
<select id="getDepartmentById" resultMap="DepartemntResultMap"> select * from department where d_id=#{id} </select> <resultMap id="DepartemntResultMap" type="Department"> <id column="d_id" property="id"></id> <result column="d_name" property="name"></result> <collection property="emps" ofType="Employee" column="d_id" select="cn.offcn.mapper.EmployeeMapper.getEmployeeByDepartId"> </collection> </resultMap> 此处变为单表查询，使分表查询方式进行查询。
4）定义 EmployeeMapper.xml 文件中的查询配置信息
public interface EmployeeMapper {
List<Employee> getEmployeeById(int i);
}
5）定义 EmployeeMapper.xml 配置文件
<resultMap id="BaseResultMap" type="employee">
<id column="e_id" property="id"></id>
<result column="e_name" property="name"></result>
<result column="e_gender" property="gender"></result>
<result column="e_age" property="age"></result>
</resultMap>
<!-- property 设置本类型中的复杂属性 javaType 复杂数据的数据类型 column 表示取sql结果集中的 指定字段 select 表示调查的查询 如果本次查询和调查的查询没有在同一个命令空间中，调用时候一定要加命名空间 -->
<resultMap id="EmployeeResultMap1" type="employee" extends="BaseResultMap">
<association property="depart" javaType="Department" column="e_depart_id" select="com.chenshuang.mapper.DepartmentMapper.getDepartmentById"></association>
</resultMap>
<!-- 根据员工id查找员工以及所在部门的所有信息【嵌套查询,分表查询】-->
<select id="getEmployeeById2" parameterType="int" resultType="Employee" resultMap="EmployeeResultMap1">
select * from employee where e_id=#{id}
</select>
6）测试方法
@Test public void testGetDepartentById() throws Exception{ //获取SqlSession对象 SqlSession session = MyBatisUtils.getSession(); //调用SqlSession 创建 UserDao接口的代理对象 DepartmentDao departmentDao = session.getMapper(DepartmentDao.class); Department dept=departmentDao.getDepartentById(1); //打印 System.out.println(dept); //提交事务 session.commit(); //关闭连接 MyBatisUtils.close(session); }
(四) MyBatis实现多对一查询
1.创建数据库表:department(部门表),employee(员工表)同时设定部门和员工表的关系
CREATE TABLE department( d_id INT NOT NULL AUTO_INCREMENT, d_name VARCHAR(100), PRIMARY KEY(d_id) ); CREATE TABLE employee( e_id INT NOT NULL AUTO_INCREMENT, e_name VARCHAR(30), e_gender VARCHAR(6), e_age INT, e_depart_id INT, PRIMARY KEY(e_id), FOREIGN KEY(e_depart_id) REFERENCES department(d_id) );
2.方式一:嵌套结果，连表查询的方式
1）创建数据模型department和employee
public class Department { private Integer id; private String name; private List<Employee> employees; } public class Employee { private Integer id; private String name; private String gender; private Integer age; private Department depart; }
2）员工持久层EmployeeMapper接口中加入查询方法
public interface EmployeeMapper { Employee getEmployeeById1(int i); }
3）部门持久层 EmployeeMapper.xml映射文件配置
<resultMap id="BaseResultMap" type="employee"> <id column="e_id" property="id"></id> <result column="e_name" property="name"></result> <result column="e_gender" property="gender"></result> <result column="e_age" property="age"></result> </resultMap> <!-- property 设置本类型中的复杂属性 javaType 复杂数据的数据类型 --> <resultMap id="EmployeeResultMap" type="employee" extends="BaseResultMap"> <association property="depart" javaType="Department"> <id column="d_id" property="id"></id> <result column="d_name" property="name"></result> </association> </resultMap> <!-- 根据员工id查找员工以及所在部门的所有信息【嵌套结果查询，联合查询】 --> <select id="getEmployeeById1" parameterType="int" resultType="Employee" resultMap="EmployeeResultMap"> SELECT e.*,d.* from employee e,department d WHERE e.e_depart_id = d.d_id AND e.e_id=#{id} </select>
4）测试方法
@Test
// 根据员工id查找员工以及所在部门的所有信息【嵌套结果查询，联合查询】
public void getEmployeeById1(){
SqlSession session = MyBatisUtils.getSession();
EmployeeMapper mapper = session.getMapper(EmployeeMapper.class);
Employee employee = mapper.getEmployeeById1(1);
System.out.println(employee.toString()+"部门---："+employee.getDepart().toString());
MyBatisUtils.close(session);
}
3.方式二:嵌套查询，分表查询的方式
1）定义员工的持久层接口DepartmentMapper
public interface DepartmentMapper { Department getDepartmentById(int id); }
2）员工持久层EmployeeMapper接口中加入查询方法
public interface EmployeeMapper { Employee getEmployeeById2(int i); List<Employee> getEmployeeById(int i); }
3）定义EmployeeMapper.xml配置文件
<resultMap id="BaseResultMap" type="employee"> <id column="e_id" property="id"></id> <result column="e_name" property="name"></result> <result column="e_gender" property="gender"></result> <result column="e_age" property="age"></result> </resultMap> <!-- property 设置本类型中的复杂属性 javaType 复杂数据的数据类型 column 表示取sql结果集中的 指定字段 select 表示调查的查询 如果本次查询和调查的查询没有在同一个命令空间中，调用时候一定要加命名空间 --> <resultMap id="EmployeeResultMap1" type="employee" extends="BaseResultMap"> <association property="depart" javaType="Department" column="e_depart_id" select="com.chenshuang.mapper.DepartmentMapper.getDepartmentById"></association> </resultMap> <!-- 根据员工id查找员工以及所在部门的所有信息【嵌套查询,分表查询】--> <select id="getEmployeeById2" parameterType="int" resultType="Employee" resultMap="EmployeeResultMap1"> select * from employee where e_id=#{id} </select>
4）定义 DepartmentMapper文件中的查询配置信息
public interface DepartmentMapper {
Department getDepartmentById(int id);
}
5）定义DepartmentMapper.xml 配置文件
<resultMap id="BaseResultMap" type="Department">
<id column="d_id" property="id"></id>
<result column="d_name" property="name"></result>
</resultMap>
<select id="getDepartmentById" parameterType="int" resultType="Department" resultMap="BaseResultMap">
select * from department where d_id=#{id}
</select>
6）测试方法
@Test // 根据员工id查找员工以及所在部门的所有信息【嵌套查询,分表查询】 public void getEmployeeById2(){ SqlSession session = MyBatisUtils.getSession(); EmployeeMapper mapper = session.getMapper(EmployeeMapper.class); Employee employee = mapper.getEmployeeById2(1); System.out.println(employee.toString()+"部门---："+employee.getDepart().toString()); MyBatisUtils.close(session); }
(五) MyBatis实现多对多查询
1.创建数据库表:student(学生表),teacher(教师表) 同时设定教师和学生表的关系 多对多
CREATE TABLE teacher( t_id INT NOT NULL auto_increment, t_name VARCHAR(30), PRIMARY KEY(t_id) ); create TABLE student_teacher( st_sid INT not NULL, st_tid INT NOT NULL, PRIMARY KEY(st_sid,st_tid), FOREIGN KEY(st_sid) REFERENCES student(s_id), FOREIGN KEY(st_tid) REFERENCES teacher(t_id) );
2.方式一:嵌套结果，连表查询的方式
1）创建数据模型Teacher和 Student 和 中间类 studentTeacher
public class Student { private Integer id; private String name; private String gender; private Integer age; private String birthday; private List<StudentTeacher> studentTeachers; } public class Teacher { private Integer id; private String name; private List<StudentTeacher> studentTeachers; } public class StudentTeacher { private Integer sid; private Integer tid; private Student student; private Teacher teacher; }
2）学生持久层StudentMapper接口中加入查询方法
public interface StudentMapper { Student getStudentById1(int i); }
3）学生持久层StudentMapper.xml映射文件配置
<!-- 根据学生id查 学生信息 和老师的信息 【嵌套结果查询，联合查询】 --> <select id="getStudentById1" parameterType="int" resultType="Student" resultMap="StudentResultMap1"> SELECT s.*,t.*,st.* FROM student s,teacher t,student_teacher st where s.id=st.st_sid AND t.t_id=st.st_tid AND s.id=#{id} </select> <resultMap id="StudentResultMap1" type="Student"> <id column="id" property="id"></id> <result column="name" property="name"></result> <result column="gender" property="gender"></result> <result column="age" property="age"></result> <result column="s_birthday" property="birthday"></result> <collection property="studentTeachers" ofType="StudentTeacher" > <result column="st_sid" property="sid"></result> <result column="st_tid" property="tid"></result> <association property="teacher" javaType="Teacher"> <id column="t_id" property="id"></id> <result column="t_name" property="name"></result> </association> </collection> </resultMap>
4）测试方法
@Test
// 根据学生id查 学生信息 和老师的信息 【嵌套结果查询，联合查询】
public void getStudentById1(){
SqlSession session = MyBatisUtils.getSession();
StudentMapper mapper = session.getMapper(StudentMapper.class);
Student student = mapper.getStudentById1(3);
System.out.println("========= 输出： ==================");
System.out.println(student);
int i=1;
for (StudentTeacher st : student.getStudentTeachers()) {
System.out.println("老师"+i+":"+st.getTeacher().getName());
i++;
}
System.out.println("=====================================");
MyBatisUtils.close(session);
}
3.方式二:嵌套查询，分表查询的方式
1）创建数据模型Teacher和 Student 和 中间类 studentTeacher
public class Student { private Integer id; private String name; private String gender; private Integer age; private String birthday; private List<StudentTeacher> studentTeachers; } public class Teacher { private Integer id; private String name; private List<StudentTeacher> studentTeachers; } public class StudentTeacher { private Integer sid; private Integer tid; private Student student; private Teacher teacher; }
2）学生持久层StudentMapper接口中加入查询方法
public interface StudentMapper { Student getStudentById2(int i); }
3）定义StudentMapper.xml配置文件
<!-- 根据学生id查 学生信息 和老师的信息 【嵌套查询，分表查询】 --> <select id="getStudentById2" parameterType="int" resultType="Student" resultMap="StudentResultMap2"> select * from student where id=#{id} </select> <resultMap id="BaseResultMap" type="Student"> <id column="id" property="id"></id> <result column="name" property="name"></result> <result column="gender" property="gender"></result> <result column="age" property="age"></result> <result column="s_birthday" property="birthday"></result> </resultMap> <resultMap id="StudentResultMap2" type="Student" extends="BaseResultMap"> <collection property="studentTeachers" ofType="StudentTeacher" column="id" select="com.chenshuang.mapper.StudentTeacherMapper.getStudentTeacherBySid"></collection> </resultMap>
4）定义 StudentTeacherMapper文件中的查询配置信息
public interface StudentTeacherMapper {
StudentTeacher getStudentTeacherBySid(int sid);
}
5）定义StudentTeacherMapper.xml 配置文件
<resultMap id="BaseResultMap" type="StudentTeacher">
<result column="st_sid" property="sid"></result>
<result column="st_tid" property="tid"></result>
</resultMap>
<resultMap id="StudentTeacherResultMap" type="StudentTeacher" extends="BaseResultMap">
<association property="teacher" javaType="Teacher" column="st_tid" select="com.chenshuang.mapper.TeacherMapper.getTeacherById">
</association>
</resultMap>
<select id="getStudentTeacherBySid" parameterType="int" resultType="StudentTeacher" resultMap="StudentTeacherResultMap">
select * from student_teacher where st_sid=#{id}
</select>
6）定义 TeacherMapper文件中的查询配置信息
public interface TeacherMapper {
Teacher getTeacherById(int id);
}
7）定义 TeacherMapper.xml 配置文件
<resultMap id="BaseResultMap" type="Teacher">
<id column="t_id" property="id"></id>
<result column="t_name" property="name"></result>
</resultMap>
<select id="getTeacherById" resultType="Teacher" parameterType="int" resultMap="BaseResultMap">
select * from teacher where t_id=#{id}
</select>
6）测试方法
@Test // 根据学生id查 学生信息 和老师的信息 【嵌套查询，分表查询】 public void getStudentById2(){ SqlSession session = MyBatisUtils.getSession(); StudentMapper mapper = session.getMapper(StudentMapper.class); Student student = mapper.getStudentById2(3); System.out.println("========= 输出： =================="); System.out.println(student); int i=1; for (StudentTeacher st : student.getStudentTeachers()) { System.out.println("老师"+i+":"+st.getTeacher().getName()); i++; } System.out.println("====================================="); MyBatisUtils.close(session); }
边栏推荐
- 在米家、欧瑞博、苹果HomeKit趋势下，智汀如何从中脱颖而出？
- y58.第三章 Kubernetes从入门到精通 -- 持续集成与部署(三一)
- Phenomenon analysis when Autowired annotation is used for list
- Redis如何实现多可用区？
- Under the trend of Micah, orebo and apple homekit, how does zhiting stand out?
- qt 简单布局 盒子模型 加弹簧
- Two person game based on bevy game engine and FPGA
- Annotation初体验
- [Oracle] simple date and time formatting and sorting problem
- 人体传感器好不好用？怎么用？Aqara绿米、小米之间到底买哪个
猜你喜欢
MySQL数据库学习（8） -- mysql 内容补充
Mysql database learning (8) -- MySQL content supplement
Is PMP really useful?
How Alibaba cloud's DPCA architecture works | popular science diagram
Use Zhiyun reader to translate statistical genetics books
Intelligent annotation scheme of entity recognition based on hugging Face Pre training model: generate doccano request JSON format
Zhang Ping'an: accelerate cloud digital innovation and jointly build an industrial smart ecosystem
If you‘re running pod install manually, make sure flutter pub get is executed first.
Record a pressure measurement experience summary
【问道】编译原理
随机推荐
【PHP SPL笔记】
MySQL数据库学习（8） -- mysql 内容补充
How Alibaba cloud's DPCA architecture works | popular science diagram
最长回文子串（动态规划）
在米家、欧瑞博、苹果HomeKit趋势下，智汀如何从中脱颖而出？
Batch size setting skills
pmp真的有用吗？
Error: No named parameter with the name ‘foregroundColor‘
Safe landing practice of software supply chain under salesforce containerized ISV scenario
Where is NPDP product manager certification sacred?
【oracle】简单的日期时间的格式化与排序问题
How can project managers counter attack with NPDP certificates? Look here
Leetcode（417）——太平洋大西洋水流问题
SQL injection cookie injection
SQL injection HTTP header injection
人体传感器好不好用？怎么用？Aqara绿米、小米之间到底买哪个
漏电继电器JELR-250FG
c语言神经网络基本代码大全及其含义
Phenomenon analysis when Autowired annotation is used for list
做自媒体，有哪些免费下载视频剪辑素材的网站？