Let's talk about the last four:
1.if、where
2.foreach
3.sql、include
Added log4j.properties: (import coordinates in pom.xml first)
<dependency> <groupId>log4j</groupId> <artifactId>log4j</artifactId> <version>1.2.17</version> </dependency>
log4j.properties：
### direct log messages to stdout ###
log4j.appender.stdout=org.apache.log4j.ConsoleAppender
log4j.appender.stdout.Target=System.out
log4j.appender.stdout.layout=org.apache.log4j.PatternLayout
log4j.appender.stdout.layout.ConversionPattern=%d{
ABSOLUTE} %5p %c{
1}:%L - %m%n
### direct messages to file mylog.log ###
log4j.appender.file=org.apache.log4j.FileAppender
log4j.appender.file.File=c:/mylog.log
log4j.appender.file.layout=org.apache.log4j.PatternLayout
log4j.appender.file.layout.ConversionPattern=%d{
ABSOLUTE} %5p %c{
1}:%L - %m%n
### set log levels - for more verbose logging change 'info' to 'debug' ###
log4j.rootLogger=debug, stdout
com.itheima.mapper/UserMapper.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.itheima.mapper.UserMapper">
<!--抽取sql片段简化编写-->
<sql id="selectSys_user">SELECT * FROM sys_user</sql>
<!--动态sql，演示if，用了sqlMapConfig的别名。代替SELECT * FROM sys_user where 1=1 and id=#{
id} and username=#{
username} and password=#{
password};-->
<select id="findByCondition" resultType="user" parameterType="user">
/*SELECT * FROM sys_user*/
<include refid="selectSys_user"></include>
<where>
<if test="id!=0">
and id=#{
id}
</if>
<if test="username!=null">
and username=#{
username}
</if>
<if test="password!=null">
and password=#{
password}
</if>
</where>
</select>
<!--演示foreach，主要代替多个条件满足一个就行 SELECT * FROM USER WHERE id IN (1,2,5)。-->
<select id="findByids" resultType="user" parameterType="list">
/*SELECT * FROM sys_user*/
<include refid="selectSys_user"></include>
<where>
<foreach collection="list" open="id in(" close=")" item="id" separator=",">
#{
id}
</foreach>
</where>
</select>
</mapper>
com.itheima.service.ServiceDemo：
package com.itheima.service;
import com.itheima.domain.Sys_user;
import com.itheima.mapper.UserMapper;
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.IOException;
import java.io.InputStream;
import java.util.ArrayList;
import java.util.List;
/**
* @author QLBF
* @version 1.0
* @date 2021/1/30 11:07
*/
public class ServiceDemo {
@Test
//条件查询动态sql，演示if
public void test1() throws IOException {
//模拟
Sys_user sys_user=new Sys_user();
sys_user.setId(2);
//sys_user.setUsername("wangwu");
//sys_user.setPassword("123");
InputStream resourceAsStream= Resources.getResourceAsStream("sqlMapConfig.xml");
SqlSessionFactory sqlSessionFactory=new SqlSessionFactoryBuilder().build(resourceAsStream);
SqlSession sqlSession=sqlSessionFactory.openSession(true);
UserMapper mapper = sqlSession.getMapper(UserMapper.class);
List<Sys_user> sys_userList = mapper.findByCondition(sys_user);
System.out.println(sys_userList);
}
@Test
//演示foreach
public void test3() throws IOException {
InputStream resourceAsStream= Resources.getResourceAsStream("sqlMapConfig.xml");
SqlSessionFactory sqlSessionFactory=new SqlSessionFactoryBuilder().build(resourceAsStream);
SqlSession sqlSession=sqlSessionFactory.openSession(true);
UserMapper mapper = sqlSession.getMapper(UserMapper.class);
//模拟ids数据
List<Integer> ids=new ArrayList<Integer>();
ids.add(2);
ids.add(7);
List<Sys_user> sys_userList = mapper.findByids(ids);
System.out.println(sys_userList);
}
}
Other codes are basically the same as the previous one: https://blog.csdn.net/GLOAL_COOK/article/details/113414561
