【JAVADAY50】Mybatis框架下，一对多关系的查询如何写，完整版
手把手教你一对多关系的查询如何写？完整版！
1、新建maven项目，修改pom.xml文件
<project xmlns="http://maven.apache.org/POM/4.0.0"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
<modelVersion>4.0.0modelVersion>
<groupId>top.keylegroupId>
<artifactId>myMYbatisartifactId>
<version>1.0-SNAPSHOTversion>
<properties>
<maven.compiler.source>17maven.compiler.source>
<maven.compiler.target>17maven.compiler.target>
properties>
<dependencies>
<dependency>
<groupId>mysqlgroupId>
<artifactId>mysql-connector-javaartifactId>
<version>8.0.28version>
dependency>
<dependency>
<groupId>org.mybatisgroupId>
<artifactId>mybatisartifactId>
<version>3.5.9version>
dependency>
<dependency>
<groupId>junitgroupId>
<artifactId>junitartifactId>
<version>4.11version>
<scope>testscope>
dependency>
<dependency>
<groupId>com.alibabagroupId>
<artifactId>druidartifactId>
<version>1.2.8version>
dependency>
dependencies>
<build>
<resources>
<resource>
<directory>src/main/javadirectory>
<includes>
<include>**/*.xmlinclude>
<include>**/*.propertiesinclude>
includes>
resource>
<resource>
<directory>src/main/resourcesdirectory>
<includes>
<include>**/*.xmlinclude>
<include>**/*.propertiesinclude>
includes>
resource>
resources>
build>
project>
2、在resource下创建jdbc.properties和SqlMapConfig.xml文件
DOCTYPE configuration PUBLIC "-//mybatis.org//DTD Config 3.0//EN"
"http://mybatis.org/dtd/mybatis-3-config.dtd">
<configuration>
<properties resource="jdbc.properties"/>
<settings>
<setting name="logImpl" value="STDOUT_LOGGING"/>
settings>
<typeAliases>
<package name="com.keyle.computer.pojo"/>
typeAliases>
<environments default="keyle">
<environment id="keyle">
<transactionManager type="JDBC"/>
<dataSource type="POOLED">
<property name="driver" value="${prop.driverClassName}"/>
<property name="url" value="${prop.url}"/>
<property name="username" value="${prop.username}"/>
<property name="password" value="${prop.password}"/>
dataSource>
environment>
environments>
<mappers>
<package name="com.keyle.computer.mapper"/>
mappers>
configuration>
prop.driverClassName=com.mysql.cj.jdbc.Driver
prop.url=jdbc:mysql://106.15.191.42:3306/ssm
prop.username=.....
prop.password=.....
问题："http://mybatis.org/dtd/mybatis-3-config.dtd"爆红，去百度搜，第一个就是解决方案。
注意：记得在可视化那里，修改连接的是哪个数据库，否则下面书写XML文件找不到表。
3、手写包装类，order和student
package com.keyle.computer.pojo;
@SuppressWarnings("all")
public class Order {
private Integer id;
private String name;
private Integer count;
private Double price;
public Integer getId() {
return id;
}
public void setId(Integer id) {
this.id = id;
}
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
public Integer getCount() {
return count;
}
public void setCount(Integer count) {
this.count = count;
}
public Double getPrice() {
return price;
}
public void setPrice(Double price) {
this.price = price;
}
@Override
public String toString() {
return "Order{" +
"id=" + id +
", name='" + name + '\'' +
", count=" + count +
", price=" + price +
'}';
}
public Order(Integer id, String name, Integer count, Double price) {
this.id = id;
this.name = name;
this.count = count;
this.price = price;
}
public Order() {
}
}
package com.keyle.computer.pojo;
import java.util.List;
@SuppressWarnings("all")
public class Student {
private Integer id;
private String name;
private String email;
private Integer age;
private List<Order> orderList;
@Override
public String toString() {
return "Student{" +
"id=" + id +
", name='" + name + '\'' +
", email='" + email + '\'' +
", age=" + age +
", orderList=" + orderList +
'}';
}
public Integer getId() {
return id;
}
public void setId(Integer id) {
this.id = id;
}
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
public String getEmail() {
return email;
}
public void setEmail(String email) {
this.email = email;
}
public Integer getAge() {
return age;
}
public void setAge(Integer age) {
this.age = age;
}
public List<Order> getOrderList() {
return orderList;
}
public void setOrderList(List<Order> orderList) {
this.orderList = orderList;
}
public Student(Integer id, String name, String email, Integer age, List<Order> orderList) {
this.id = id;
this.name = name;
this.email = email;
this.age = age;
this.orderList = orderList;
}
public Student() {
}
}
注意：看我每个类写了哪些字段，哪些是数据库中有，但我没写的。
5、创建…Mapper和对应的同名的XML文件
DOCTYPE mapper PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN"
"http://mybatis.org/dtd/mybatis-3-mapper.dtd">
<mapper namespace="com.keyle.computer.mapper.CustomerMapper">
mapper>
package com.keyle.computer.mapper;
@SuppressWarnings("all")
public interface CustomerMapper {
}
注意：XML文件一定要写namespace
6、先在查询控制台写SQL语句
select s.id as 'userid', s.name as 'username', email, age, t.id as 'orderid', t.name as 'ordername', count, price, customer_id
from student s left join t_order t on s.id = t.customer_id
where s.id=1;
7、手写CustomerMapper.xml
DOCTYPE mapper PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN"
"http://mybatis.org/dtd/mybatis-3-mapper.dtd">
<mapper namespace="com.keyle.computer.mapper.CustomerMapper">
<resultMap id="customermap" type="student">
<id property="id" column="userid"/>
<result property="name" column="username"/>
<result property="email" column="email"/>
<result property="age" column="age"/>
<collection property="orderList" ofType="order">
<id property="id" column="orderid"/>
<result property="name" column="ordername"/>
<result property="count" column="count"/>
<result property="price" column="price"/>
collection>
resultMap>
<select id="byIdGetStudentAndOrder" parameterType="int" resultMap="customermap">
select s.id as 'userid', s.name as 'username', email, age, t.id as 'orderid', t.name as 'ordername', count, price, customer_id
from student s left join t_order t on s.id = t.customer_id
where s.id = #{id}
select>
mapper>
注意：最重要的莫属：多的那个属性的绑定orderList
8、手写接口，与xml文件同名且方法名同名
package com.keyle.computer.mapper;
import com.keyle.computer.pojo.Student;
@SuppressWarnings("all")
public interface CustomerMapper {
//根据用户ID查出其信息，以及其拥有的订单信息
Student byIdGetStudentAndOrder(Integer id);
}
9、手写测试方法
import com.keyle.computer.mapper.CustomerMapper;
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.After;
import org.junit.Before;
import org.junit.Test;
import java.io.IOException;
import java.io.InputStream;
public class myTest {
SqlSession sqlSession;
CustomerMapper cm;
@Before
public void before() throws IOException {
InputStream inputStream = Resources.getResourceAsStream("SqlMapConfig.xml");
SqlSessionFactory factory = new SqlSessionFactoryBuilder().build(inputStream);
sqlSession = factory.openSession();
cm = sqlSession.getMapper(CustomerMapper.class);
}
@After
public void after(){
sqlSession.close();
}
@Test
public void MyTestA(){
System.out.println(cm.byIdGetStudentAndOrder(1));
}
}
运行结果：
Student{id=1, name='张三', email='[email protected]', age=22, orderList=[Order{id=1, name='苹果', count=20, price=12.8}, Order{id=2, name='橘子', count=11, price=21.8}]}
成功！