MyBatis多表查询
多表模型分类
一对一:在任意一方建立外键,关联对方的主键。
一对多:在多的一方建立外键,关联一的一方的主键。
多对多:借助中间表,中间表至少两个字段,分别关联两张表的主键。
数据准备
sql
CREATE DATABASE db2;
USE db2;
-- 创建person表
CREATE TABLE person(
id INT PRIMARY KEY AUTO_INCREMENT,
NAME VARCHAR(20),
age INT
);
INSERT INTO person VALUES (NULL,'张三',23);
INSERT INTO person VALUES (NULL,'李四',24);
INSERT INTO person VALUES (NULL,'王五',25);
-- 创建card表
CREATE TABLE card(
id INT PRIMARY KEY AUTO_INCREMENT,
number VARCHAR(30),
pid INT,
CONSTRAINT cp_fk FOREIGN KEY (pid) REFERENCES person(id)
);
INSERT INTO card VALUES (NULL,'12345',1);
INSERT INTO card VALUES (NULL,'23456',2);
INSERT INTO card VALUES (NULL,'34567',3);
-- 创建班级表
CREATE TABLE classes(
id INT PRIMARY KEY AUTO_INCREMENT,
NAME VARCHAR(20)
);
INSERT INTO classes VALUES (NULL,'一班');
INSERT INTO classes VALUES (NULL,'二班');
-- 创建学生表
CREATE TABLE student(
id INT PRIMARY KEY AUTO_INCREMENT,
NAME VARCHAR(30),
age INT,
cid INT,
CONSTRAINT cs_fk FOREIGN KEY (cid) REFERENCES classes(id)
);
INSERT INTO student VALUES (NULL,'张三',23,1);
INSERT INTO student VALUES (NULL,'李四',24,1);
INSERT INTO student VALUES (NULL,'王五',25,2);
INSERT INTO student VALUES (NULL,'赵六',26,2);
-- 创建课程表
CREATE TABLE course(
id INT PRIMARY KEY AUTO_INCREMENT,
NAME VARCHAR(20)
);
INSERT INTO course VALUES (NULL,'语文');
INSERT INTO course VALUES (NULL,'数学');
-- 学生表与课程表的中间表
CREATE TABLE stu_cr(
id INT PRIMARY KEY AUTO_INCREMENT,
sid INT,
cid INT,
CONSTRAINT sc_fk1 FOREIGN KEY (sid) REFERENCES student(id),
CONSTRAINT sc_fk2 FOREIGN KEY (cid) REFERENCES course(id)
);
INSERT INTO stu_cr VALUES (NULL,1,1);
INSERT INTO stu_cr VALUES (NULL,1,2);
INSERT INTO stu_cr VALUES (NULL,2,1);
INSERT INTO stu_cr VALUES (NULL,2,2);
表之间的关系
多表操作之XML
目录结构
MyBatis核心配置文件以及jdbc,log4j配置文件放在src目录下
MyBatis核心配置文件
<?xml version="1.0" encoding="UTF-8" ?>
<!--MyBatis的DTD约束-->
<!DOCTYPE configuration PUBLIC "-//mybatis.org//DTD Config 3.0//EN" "http://mybatis.org/dtd/mybatis-3-config.dtd">
<!--configuration 核心根标签-->
<configuration>
<!--引入数据库连接的配置文件-->
<properties resource="jdbc.properties"/>
<!--配置LOG4J-->
<settings>
<setting name="logImpl" value="log4j"/>
</settings>
<!--起别名-->
<typeAliases>
<package name="com.fs.bean"/>
</typeAliases>
<!--environments配置数据库环境,环境可以有多个。default属性指定使用的是哪个-->
<environments default="mysql">
<!--environment配置数据库环境 id属性唯一标识-->
<environment id="mysql">
<!-- transactionManager事务管理。 type属性,采用JDBC默认的事务-->
<transactionManager type="JDBC"></transactionManager>
<!-- dataSource数据源信息 type属性 连接池-->
<dataSource type="POOLED">
<!-- property获取数据库连接的配置信息 -->
<property name="driver" value="${driver}" />
<property name="url" value="${url}" />
<property name="username" value="${username}" />
<property name="password" value="${password}" />
</dataSource>
</environment>
</environments>
<!-- mappers引入映射配置文件 -->
<mappers>
<mapper resource="com/fs/one_to_one/OneToOneMapper.xml"/>
<mapper resource="com/fs/one_to_many/OneToManyMapper.xml"/>
<mapper resource="com/fs/many_to_many/ManyToManyMapper.xml"/>
<!--若为注解,就配置注解扫描的包 -->
<!--配置映射关系-->
<mappers>
<package name="com.fs"/>
</mappers>
</mappers>
</configuration>
jdbc配置文件
driver=com.mysql.jdbc.Driver
url=jdbc:mysql://192.168.93.132:3306/db2
username=root
password=root
log4j配置文件
# Global logging configuration
# ERROR WARN INFO DEBUG
log4j.rootLogger=DEBUG, stdout
# Console output...
log4j.appender.stdout=org.apache.log4j.ConsoleAppender
log4j.appender.stdout.layout=org.apache.log4j.PatternLayout
log4j.appender.stdout.layout.ConversionPattern=%5p [%t] - %m%n
bean实体类
一对一的多表查询XML
OneToOneMapper.xml
<?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="com.fs.table01.OneToOneMapper">
<!--配置字段和实体对象属性的映射关系
resultMap:配置映射关系,方法的返回值,
id:起个名字
type:那个实体对象的别名-->
<resultMap id="oneToOne" type="card">
<!--id:配置主键标签
column:查询结果的字段名
property:实体类中对应的属性名-->
<id column="cid" property="id" />
<!-- result:其余字段配置标签-->
<result column="number" property="number" />
<!-- association:配置被包含对象的映射关系
property:被包含对象的变量名
javaType:被包含对象的数据类型-->
<association property="p" javaType="person">
<id column="pid" property="id" />
<result column="name" property="name" />
<result column="age" property="age" />
</association>
</resultMap>
<!--resultMap:多表查询属性封装-->
<select id="selectAll" resultMap="oneToOne">
SELECT c.id cid,number,pid,NAME,age FROM card c,person p WHERE c.pid=p.id
</select>
</mapper>
映射接口
OneToOneMapper
package com.fs.table01;
import com.fs.bean.Card;
import java.util.List;
public interface OneToOneMapper {
//查询全部
public abstract List<Card> selectAll();
}
测试类
package com.fs.table01;
import com.fs.bean.Card;
import org.apache.ibatis.io.Resources;
import org.apache.ibatis.session.SqlSession;
import org.apache.ibatis.session.SqlSessionFactory;
import org.apache.ibatis.session.SqlSessionFactoryBuilder;
import org.junit.Test;
import java.io.InputStream;
import java.util.List;
public class Test01 {
@Test
public void selectAll() throws Exception{
//1.加载核心配置文件
InputStream is = Resources.getResourceAsStream("MyBatisConfig.xml");
//2.获取SqlSession工厂对象
SqlSessionFactory sqlSessionFactory = new SqlSessionFactoryBuilder().build(is);
//3.通过工厂对象获取SqlSession对象
SqlSession sqlSession = sqlSessionFactory.openSession(true);
//4.获取OneToOneMapper接口的实现类对象
OneToOneMapper mapper = sqlSession.getMapper(OneToOneMapper.class);
//5.调用实现类的方法,接收结果
List<Card> list = mapper.selectAll();
//6.处理结果
for (Card c : list) {
System.out.println(c);
}
//7.释放资源
sqlSession.close();
is.close();
}
}
一对一XML图解
一对多的表查询XML
OneToManyMapper.xml
<?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="com.fs.table02.OneToManyMapper">
<resultMap id="oneToMany" type="classes">
<id column="cid" property="id"/>
<result column="cname" property="name"/>
<!--
collection:配置被包含的集合对象映射关系
property:被包含对象的变量名
ofType:被包含对象的实际数据类型
-->
<collection property="students" ofType="student">
<id column="sid" property="id"/>
<result column="sname" property="name"/>
<result column="sage" property="age"/>
</collection>
</resultMap>
<select id="selectAll" resultMap="oneToMany">
SELECT c.id cid,c.name cname,s.id sid,s.name sname,s.age sage FROM classes c,student s WHERE c.id=s.cid
</select>
</mapper>
OneToManyMapper
package com.fs.table02;
import com.fs.bean.Classes;
import java.util.List;
public interface OneToManyMapper {
//查询全部
public abstract List<Classes> selectAll();
}
测试类
package com.fs.table02;
import com.fs.bean.Classes;
import com.fs.bean.Student;
import org.apache.ibatis.io.Resources;
import org.apache.ibatis.session.SqlSession;
import org.apache.ibatis.session.SqlSessionFactory;
import org.apache.ibatis.session.SqlSessionFactoryBuilder;
import org.junit.Test;
import java.io.InputStream;
import java.util.List;
public class Test01 {
@Test
public void selectAll() throws Exception{
//1.加载核心配置文件
InputStream is = Resources.getResourceAsStream("MyBatisConfig.xml");
//2.获取SqlSession工厂对象
SqlSessionFactory sqlSessionFactory = new SqlSessionFactoryBuilder().build(is);
//3.通过工厂对象获取SqlSession对象
SqlSession sqlSession = sqlSessionFactory.openSession(true);
//4.获取OneToManyMapper接口的实现类对象
OneToManyMapper mapper = sqlSession.getMapper(OneToManyMapper.class);
//5.调用实现类的方法,接收结果
List<Classes> classes = mapper.selectAll();
//6.处理结果
for (Classes cls : classes) {
System.out.println(cls.getId() + "," + cls.getName());
List<Student> students = cls.getStudents();
for (Student student : students) {
System.out.println("\t" + student);
}
}
//7.释放资源
sqlSession.close();
is.close();
}
}
一对多XML图解
多对多的多表查询XML
ManyToManyMapper.xml
<?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="com.fs.table03.ManyToManyMapper">
<!--配置字段和实体对象属性的映射关系
resultMap:配置映射关系,方法的返回值,
id:起个名字
type:那个实体对象的别名-->
<resultMap id="manyToMany" type="student">
<!--id:配置主键标签
column:查询结果的字段名
property:实体类中对应的属性名-->
<id column="sid" property="id"/>
<result column="sname" property="name"/>
<result column="sage" property="age"/>
<!--
collection:配置被包含的集合对象映射关系
property:被包含对象的变量名
ofType:被包含对象的实际数据类型
-->
<collection property="courses" ofType="course">
<id column="cid" property="id"/>
<result column="cname" property="name"/>
</collection>
</resultMap>
<resultMap id="selectCourse" type="course">
<id column="cid" property="id"/>
<result column="cname" property="name"/>
<collection property="students" ofType="student">
<id column="sid" property="id"/>
<result column="sname" property="name"/>
<result column="sage" property="age"/>
</collection>
</resultMap>
<select id="selectAll" resultMap="manyToMany">
SELECT sc.sid,s.name sname,s.age sage,sc.cid,c.name cname FROM student s,course c,stu_cr sc WHERE
sc.sid=s.id AND sc.cid=c.id
</select>
<select id="selectAllCourse" resultMap="selectCourse">
SELECT sc.sid,s.name sname,s.age sage,sc.cid,c.name cname FROM student s,course c,stu_cr sc WHERE
sc.sid=s.id AND sc.cid=c.id
</select>
</mapper>
ManyToManyMapper
package com.fs.table03;
import com.fs.bean.Course;
import com.fs.bean.Student;
import java.util.List;
public interface ManyToManyMapper {
//查询全部
public abstract List<Student> selectAll();
List<Course> selectAllCourse();
}
** 测试类 **
package com.fs.table03;
import com.fs.bean.Course;
import com.fs.bean.Student;
import org.apache.ibatis.io.Resources;
import org.apache.ibatis.session.SqlSession;
import org.apache.ibatis.session.SqlSessionFactory;
import org.apache.ibatis.session.SqlSessionFactoryBuilder;
import org.junit.Test;
import java.io.InputStream;
import java.util.List;
public class Test01 {
@Test
public void selectAll() throws Exception{
//1.加载核心配置文件
InputStream is = Resources.getResourceAsStream("MyBatisConfig.xml");
//2.获取SqlSession工厂对象
SqlSessionFactory sqlSessionFactory = new SqlSessionFactoryBuilder().build(is);
//3.通过工厂对象获取SqlSession对象
SqlSession sqlSession = sqlSessionFactory.openSession(true);
//4.获取ManyToManyMapper接口的实现类对象
ManyToManyMapper mapper = sqlSession.getMapper(ManyToManyMapper.class);
//5.调用实现类的方法,接收结果
List<Student> students = mapper.selectAll();
//6.处理结果
for (Student student : students) {
System.out.println(student.getId() + "," + student.getName() + "," + student.getAge());
List<Course> courses = student.getCourses();
for (Course cours : courses) {
System.out.println("\t" + cours);
}
}
//7.释放资源
sqlSession.close();
is.close();
}
@Test
public void selectAllCourse() throws Exception{
//1.加载核心配置文件
InputStream is = Resources.getResourceAsStream("MyBatisConfig.xml");
//2.获取SqlSession工厂对象
SqlSessionFactory sqlSessionFactory = new SqlSessionFactoryBuilder().build(is);
//3.通过工厂对象获取SqlSession对象
SqlSession sqlSession = sqlSessionFactory.openSession(true);
//4.获取ManyToManyMapper接口的实现类对象
ManyToManyMapper mapper = sqlSession.getMapper(ManyToManyMapper.class);
List<Course> courses = mapper.selectAllCourse();
//5.调用实现类的方法,接收结果
for (Course cours : courses) {
System.out.println("课程编号:"+cours.getId()+","+"课程名字:"+cours.getName());
List<Student> students = cours.getStudents();
for (Student student : students) {
System.out.println(student);
}
}
//7.释放资源
sqlSession.close();
is.close();
}
}
多对多的图解
多表操作之注解
项目结构
由于项目结构差不多,我这里就直接图解,相当于配置文件删除了,多了接口,让MyBatis动态代理生成实现类,来完成操作
一对一的多表查询注解图解
一对多的多表查询注解图解
多对多的表查询注解图解
多表查询小结:
多表操作-XML
多表模型分类:一对一、一对多、多对多。
<resultMap>:配置字段和对象属性的映射关系标签。
id 属性:唯一标识
type 属性:实体对象类型
<id>:配置主键映射关系标签。
<result>:配置非主键映射关系标签。
column 属性:表中字段名称
property 属性: 实体对象变量名称
<association>:配置被包含对象的映射关系标签。
property 属性:被包含对象的变量名
javaType 属性:被包含对象的数据类型
<collection>:配置被包含集合对象的映射关系标签。
property 属性:被包含集合对象的变量名
ofType 属性:集合中保存的对象数据类型
注解多表操作
@Results:封装映射关系的父注解。
Result[] value():定义了 Result 数组
@Result:封装映射关系的子注解。
column 属性:查询出的表中字段名称
property 属性:实体对象中的属性名称
javaType 属性:被包含对象的数据类型
one 属性:一对一查询固定属性
many 属性:一对多查询固定属性
@One:一对一查询的注解。
select 属性:指定调用某个接口中的方法
@Many:一对多查询的注解。
select 属性:指定调用某个接口中的方法