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总结MyBatis知识点

zmhc 2022-04-06 阅读 38

目录

1、 MyBatis是什么?

2、Mybatis解决哪些问题?

3、开始创建工程

【1】创建Maven项目

【2】pom.xml依赖

 【3】mybatis.xml依赖

【4】实体类

 【6】测试类

【7】发现一个BUG,Team.xml

【8】结果

 【9】改进,使用@Before@After

 4、日志的使用

【1】pom.xml

【2】log4j.properties

【3】mybatis.xml

【4】结果

 5、建造者设计模式介绍

6、#{} 和 ${}的区别

【1】#{}

【2】${}

7、动态SQL

更新

8、分页

【1】pom.xml

【2】mybatis.xml

【3】测试

9、Mybatis缓存

【1】 一级缓存

【2】二级缓存

【3】清空缓存的方式


1、 MyBatis是什么?

官网:mybatis – MyBatis 3 | 简介

2、Mybatis解决哪些问题

3、开始创建工程

【1】创建Maven项目

【2】pom.xml依赖

<?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>
<!--自定义-->
<groupId>com.qinluyu</groupId>
<artifactId>Mybatis01</artifactId>
<version>1.0-SNAPSHOT</version>
<!--Mybatis-->
<dependencies>
<dependency>
<groupId>org.mybatis</groupId>
<artifactId>mybatis</artifactId>
<version>3.5.7</version>
</dependency>
<!--mysql-->
<dependency>
<groupId>mysql</groupId>
<artifactId>mysql-connector-java</artifactId>
<!--mysql版本5-6之间-->
<version>5.1.45</version>
</dependency>
<!--测试test-->
<dependency>
<groupId>junit</groupId>
<artifactId>junit</artifactId>
<version>4.12</version>
<scope>test</scope>
</dependency>
</dependencies>
<build>
<plugins>
<plugin>
<!--maven-->
<groupId>org.apache.maven.plugins</groupId>
<artifactId>maven-compiler-plugin</artifactId>
<version>3.8.1</version>
<configuration>
<!--jdk-->
<target>1.8</target>
<source>1.8</source>
</configuration>

</plugin>
</plugins>
</build>
</project>

 【3】mybatis.xml依赖

<?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>
<environments default="development">
<environment id="development">
<transactionManager type="JDBC"/>
<dataSource type="POOLED">
<property name="driver" value="com.mysql.jdbc.Driver"/>
<property name="url" value="jdbc:mysql://localhost:3306/mybatis?useUnicode=truecharacterEncoding=utf-8useSSL=falseserverTimezone=GMT"/>
<property name="username" value="${root}"/>
<property name="password" value="${123}"/>
</dataSource>
</environment>
</environments>
<!--映射文件-->
<mappers>
<mapper resource="com.qinluyu.Dao.Team.xml"/>
</mappers>
</configuration>

【4】实体类

public class Team {
private Integer teamId;
private String teamName;
private String location;
private Date createTime;
get/set方法
tostring方法

【5】实体类的映射文件

 【6】测试类

private String resource="mybatis.xml";
@Test
public void test02(){
SqlSession sqlSession=null;
try{
Reader reader=Resources.getResourceAsReader(resource);
SqlSessionFactory factory=new SqlSessionFactoryBuilder().build(reader);//根据图纸创建出了工厂
sqlSession=factory.openSession();
//执行sql
List<Team> list=sqlSession.selectList("com.qinluyu.Dao.Team.queryAll");
//遍历结果
for(Team team:list){
System.out.println(team);
}
}catch(IOException e){
e.printStackTrace();
}finally{
//关闭资源
sqlSession.close();
}

【7】发现一个BUG,Team.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.qinluyu.pojo.Team">
<!--查询,id为自定义名称,相当于dao-->
<select id="queryAll" resultType="com.qinluyu.pojo.Team">

<!--<select id="queryAll" resultMap="com.qinluyu.pojo.Team">-->此为BUG
select * from team;
</select>

</mapper>

【8】结果

 【9】改进,使用@Before@After

public class TestTeam {
private String resource="mybatis.xml";
private SqlSession sqlSession;
@Test
public void test02(){
System.out.println("改进————,查询单个");
Team team = sqlSession.selectOne("com.qinluyu.pojo.Team.queryOne", 1002);
System.out.println(team);
}
@Before
public void before(){
Reader reader=null;
try {
reader=Resources.getResourceAsReader(resource);
} catch (IOException e) {
e.printStackTrace();
}
SqlSessionFactory factory=new SqlSessionFactoryBuilder().build(reader);
sqlSession=factory.openSession();
}
@After
public void after(){
sqlSession.close();
}

 4、日志的使用

【1】pom.xml

<!--日志的使用-->
<dependency>
<groupId>log4j</groupId>
<artifactId>log4j</artifactId>
<version>1.2.17</version>
</dependency>

【2】log4j.properties

# Global logging configuration  info  warning  error
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

【3】mybatis.xml

<!--注意顺序
configuration (properties?, settings?, typeAliases?, typeHandlers?, objectFactory?, objectWrapperFactory?, reflectorFactory?, plugins?, environments?, databaseIdProvider?, mappers
-->

<settings>
<setting name="logImpl" value="LOG4J"/>
</settings>

【4】结果

 5、建造者设计模式介绍

6、#{} ${}的区别

【1】#{}

【2】${}

7、动态SQL

更新

<update id="updateAuthorIfNecessary">
update Author
<set>
<if test="username != null">username=#{username},</if>
<if test="password != null">password=#{password},</if>
<if test="email != null">email=#{email},</if>
<if test="bio != null">bio=#{bio}</if>
</set>
where id=#{id}
</update>

8、分页

【1】pom.xml

<dependency>
<groupId>com.github.pagehelper</groupId>
<artifactId>pagehelper</artifactId>
<version>5.2.0</version>
</dependency>

【2】mybatis.xml

<!--分页-->
<plugins>
<plugin interceptor="com.github.pagehelper.PageInterceptor"></plugin>
<!--<property name="reasonable" value="true"/>-->
</plugins>

【3】测试

public void test5() {
// PageHelper.startPage 必须紧邻查询语句,而且只对第一条查询语句生效
PageHelper.startPage(2, 5);
List<Team> teams = teamMapper.queryAll();//查询语句结尾不能有分号
teams.forEach(team -> System.out.println(team));
PageInfo<Team> info = new PageInfo<>(teams);
System.out.println("分页信息如下:");
System.out.println("当前页:" + info.getPageNum());
System.out.println("总页数:" + info.getPages());
System.out.println("前一页:" + info.getPrePage());
System.out.println("后一页:" + info.getNextPage());
System.out.println("navigatepageNums:" + info.getNavigatepageNums());
for (int num : info.getNavigatepageNums()) {
System.out.println(num);
}

9、Mybatis缓存

【1】 一级缓存

【2】二级缓存

【3】清空缓存的方式

后续还有补充,有点难,先停一下

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