Mybatis的SQL语句返回结果有两种
- resultType
- 查询出的字段在相应的POJO中必须有和它相同的字段对应，或者基本数据类型
- 适合简单查询
- resultMap
- 需要自定义字段，或者多表查询，一对多等关系，比resultType更强大
- 适合复杂查询
项目结构
pom.xml
<?xml version="1.0" encoding="UTF-8"?>
<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>4.0.0</modelVersion>
<groupId>net.cyb</groupId>
<artifactId>cyb-mybatis</artifactId>
<version>1.0-SNAPSHOT</version>
<dependencies>
<dependency>
<groupId>org.mybatis</groupId>
<artifactId>mybatis</artifactId>
<version>3.5.4</version>
</dependency>
<dependency>
<groupId>mysql</groupId>
<artifactId>mysql-connector-java</artifactId>
<version>8.0.20</version>
</dependency>
<dependency>
<groupId>org.slf4j</groupId>
<artifactId>slf4j-log4j12</artifactId>
<version>1.7.30</version>
</dependency>
</dependencies>
</project>
mybatis-config.xml
<!DOCTYPE configuration
PUBLIC "-//mybatis.org//DTD Config 3.0//EN"
"http://mybatis.org/dtd/mybatis-3-config.dtd">
<configuration>
<!-- 引入外部配置文件 -->
<properties resource="config/db.properties"></properties>
<!--下划线自动映射驼峰字段-->
<settings>
<setting name="mapUnderscoreToCamelCase" value="true"/>
</settings>
<!-- 数据库链接相关 -->
<environments default="development">
<environment id="development">
<transactionManager type="JDBC" />
<dataSource type="POOLED">
<property name="driver" value="${db.driver}" />
<property name="url" value="${db.url}" />
<property name="username" value="${db.username}" />
<property name="password" value="${db.password}" />
</dataSource>
</environment>
</environments>
<mappers>
<!-- 添加映射文件 -->
<mapper resource="mapper/VideoMapper.xml" />
</mappers>
</configuration>
db.properties
db.driver=com.mysql.cj.jdbc.Driver
db.url=jdbc:mysql://127.0.0.1:3306/cybclass
db.username=root
db.password=root
log4j.properties
#dev env [debug] product env [info]
log4j.rootLogger=ERROR, stdout
# Console output...
# 细化到打印某个mapper
# log4j.logger.包名.方法名=TRACE
log4j.logger.net.cybclass.online=TRACE
#log4j.logger.net.cybclass.online.dao.VideoMapper.selectById=TRACE
log4j.appender.stdout=org.apache.log4j.ConsoleAppender
log4j.appender.stdout.layout=org.apache.log4j.PatternLayout
log4j.appender.stdout.layout.ConversionPattern=%5p [%t] - %m%n
VideoMapper.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">
<!--
namespace：名称空间，一般需要保持全局唯一，最好是和dao层的java接口一致。可以映射sql语句到对应的方法名称和参数、返回类型
-->
<mapper namespace="net.cybclass.online.dao.VideoMapper">
<resultMap id="videoResultMap" type="net.cybclass.online.domain.Video">
<id column="id" property="id" jdbcType="INTEGER"></id>
<result column="title2" property="title" jdbcType="VARCHAR"></result>
<result column="summary" property="summary" jdbcType="VARCHAR"></result>
</resultMap>
<sql id="base_video_field2">id,title title2,summary</sql>
<select id="selectBaseFieldByIdWithResultMap" resultMap="videoResultMap">
select <include refid="base_video_field2"></include> from video where id=#{id}
</select>
</mapper>
VideoMapper.java
package net.cybclass.online.dao;
import net.cybclass.online.domain.Video;
import org.apache.ibatis.annotations.Param;
import org.apache.ibatis.annotations.Select;
import java.util.List;
import java.util.Map;
public interface VideoMapper {
Video selectBaseFieldByIdWithResultMap(int id);
}
Video.java
package net.cybclass.online.domain;
import java.util.Date;
/**
* 视频类
*/
public class Video {
//内码
private int id;
//视频标题
private String title;
//视频详情
private String summary;
//视频封面
private String coverImg;
//加个
private int price;
private int c_id;
//评分
private double point;
//创建日期
private Date create_time;
public int getId() {
return id;
}
public void setId(int id) {
this.id = id;
}
public String getTitle() {
return title;
}
public void setTitle(String title) {
this.title = title;
}
public String getSummary() {
return summary;
}
public void setSummary(String summary) {
this.summary = summary;
}
public String getCoverImg() {
return coverImg;
}
public void setCoverImg(String coverImg) {
this.coverImg = coverImg;
}
public int getPrice() {
return price;
}
public void setPrice(int price) {
this.price = price;
}
public int getC_id() {
return c_id;
}
public void setC_id(int c_id) {
this.c_id = c_id;
}
public double getPoint() {
return point;
}
public void setPoint(double point) {
this.point = point;
}
public Date getCreate_time() {
return create_time;
}
public void setCreate_time(Date create_time) {
this.create_time = create_time;
}
@Override
public String toString() {
return "Video{" +
"id=" + id +
", title='" + title + '\'' +
", summary='" + summary + '\'' +
", coverImg='" + coverImg + '\'' +
", price=" + price +
", c_id=" + c_id +
", point=" + point +
", create_time=" + create_time +
'}';
}
}
SqlSessionDemo.java
package net.cybclass.online;
import net.cybclass.online.dao.VideoMapper;
import net.cybclass.online.domain.Video;
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 java.io.IOException;
import java.io.InputStream;
import java.util.*;
public class SqlSessionDemo {
public static void main(String[] args) throws IOException {
String resouce="config/mybatis-config.xml";
InputStream resourceAsStream = Resources.getResourceAsStream(resouce);
SqlSessionFactory build = new SqlSessionFactoryBuilder().build(resourceAsStream);
try(SqlSession session=build.openSession()){
VideoMapper mapper = session.getMapper(VideoMapper.class);
Video video = mapper.selectBaseFieldByIdWithResultMap(52);
System.out.println(video.toString());
}catch (Exception e){
e.printStackTrace();
}
}
}
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