标签：name student int sex Student sid Mybatis
Mybatis
基本使用
- 创建工具类来构造SqlSessionFactory
public class MybatisUtil {
//在类加载时就进行创建
private static SqlSessionFactory sqlSessionFactory;
static {
try {
sqlSessionFactory = new SqlSessionFactoryBuilder().build(new FileInputStream("mybatis-config.xml"));
} catch (FileNotFoundException e) {
e.printStackTrace();
}
}
/**
* 获取一个新的会话
* @param autoCommit 是否开启自动提交（跟JDBC是一样的，如果不自动提交，则会变成事务操作）
* @return SqlSession对象
*/
public static SqlSession getSession(boolean autoCommit){
return sqlSessionFactory.openSession(autoCommit);
}
}
- main方法更简单
package com.test;
import com.test.Util.MybatisUtil;
import com.test.mapper.TestMapper;
import org.apache.ibatis.session.SqlSession;
import java.awt.print.Book;
import java.util.List;
public class Main {
public static void main(String[] args) {
MybatisUtil.getSession(true).getMapper(TestMapper.class).selectStudent().forEach(System.out::println);
}
}
- entity.Student
package com.test.entity;
import lombok.Data;
@Data
public class Student {
int sid;
String name;
String sex;
int grade;
}
- mapper.TestMapper.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.test.mapper.TestMapper">
<select id="selectStudent" resultType="com.test.entity.Student">
select * from book_manage.student
</select>
</mapper>
- mapper.TestMapper
package com.test.mapper;
import com.test.entity.Student;
import java.awt.print.Book;
import java.util.List;
public interface TestMapper {
List<Student> selectStudent();
}
- mybatis-config.xml
<?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.cj.jdbc.Driver"/>
<property name="url" value="jdbc:mysql://localhost:3306/book_manage"/>
<property name="username" value="root"/>
<property name="password" value="123456"/>
</dataSource>
</environment>
</environments>
<mappers>
<mapper resource="com/test/mapper/TestMapper.xml"/>
</mappers>
</configuration>
起别名
-
Student.java
@Alias("MiKu") public class Student { int sid; String name; String sex; int grade; }mybatis-config.xml
<typeAliases> <package name="com.test.entity"/> </typeAliases>TestMapper.xml
<mapper namespace="com.test.mapper.TestMapper">
<select id="selectStudent" resultType="MiKu">
select * from book_manage.student
</select>
</mapper>
- mybatis-config.xml
<!-- 需要在environments的上方 -->
<typeAliases>
<typeAlias type="com.test.entity.Student" alias="Student"/>
</typeAliases>
TestMapper.xml
<mapper namespace="com.test.mapper.TestMapper">
<select id="selectStudent" resultType="Student">
select * from book_manage.student
</select>
</mapper>
- mybatis-config.xml
<typeAliases>
<package name="com.test.entity"/>
</typeAliases>
TestMapper.xml
<select id="selectStudent" resultType="student">
select * from book_manage.student
</select>
增
<insert id="addStudent" >
insert into student(name,age) values (#{name},#{age})
</insert>
int addStudent(Student student);
System.out.println(mapper.addStudent(new Student().setName("白牛").setAge(88)));
删
<delete id="deleteStudent">
delete from student where id = #{id}
</delete>
int deleteStudent(int id);
System.out.println(mapper.deleteStudent(16));
改
<update id="updateStudent">
update student
set name=#{name},age=#{age}
where id = #{id}
</update>
int updateStudent(Student student);
System.out.println(mapper.updateStudent(new Student(2,"cat",999)));
查
<select id="selectStudentById" resultType="Student">
select * from student where id = #{id}
</select>
Student selectStudentById(int id);
System.out.println(mapper.selectStudentById(3));
用Map映射
<resultMap id="Test" type="Student">
<result column="id" property="age"/>
<result column="name" property="name"/>
<result column="age" property="id"/>
</resultMap>
<select id="selectStudent" resultType="Map">
select * from student
</select>
List<Student> selectStudent();
mapper.selectStudent().forEach(System.out::println);
构造器问题
一个类中存在多个构造方法，会报错
<resultMap id="Test" type="Student">
<constructor>
<arg column="id" javaType="int"/>
<arg column="name" javaType="String"/>
</constructor>
</resultMap>
<select id="selectStudent" resultMap="Test">
select * from student
</select>
@Data
@Accessors(chain = true)
public class Student {
public Student(Integer id, String name) {
this.id = id;
this.name = name;
}
int id;
String name;
int age;
}
驼峰命名
数据库是下划线命名，java是驼峰命名，可以进行转换
<settings>
<setting name="mapUnderscoreToCamelCase" value="true"/>
</settings>
下划线命名 -> 驼峰命名
事务操作
SqlSession session = MybatisUtil.getSession(false); // 开启事务
session.rollback(); // 回滚
session.commit(); // 提交
缓存机制
概念
把一部分内容放入缓存，下次获取数据，直接从缓存读取，直接从内存获取，而不是向数据库索要，效率更高
一级缓存
Mybatis默认启动一级缓存
作用范围有限，作用于一个会话，我们希望缓存扩展到所有会话，通过二级缓存，默认关闭
<cache
eviction="FIFO"
flushInterval="60000"
size="512"
readOnly="true"/>
某个方法关闭缓存
<select id="getStudentBySid" resultType="Student" useCache="false">
select * from student where sid = #{sid}
</select>
操作完成后清空缓存
<select id="getStudentBySid" resultType="Student" flushCache="true">
select * from student where sid = #{sid}
</select>
读取顺序：二级缓存 => 一级缓存 => 数据库
注解开发
@Insert("insert into student(name, sex) values(#{name}, #{sex})")
int addStudent(Student student);
<mappers>
<mapper class="com.test.mapper.MyMapper"/>
<!-- 也可以直接注册整个包下的 <package name="com.test.mapper"/> -->
</mappers>
指定构造方法
@ConstructorArgs({
@Arg(column = "sid", javaType = int.class),
@Arg(column = "name", javaType = String.class)
})
@Select("select * from student where sid = #{sid} and sex = #{sex}")
Student getStudentBySidAndSex(@Param("sid") int sid, @Param("sex") String sex);
指定参数类型
@Select("select * from student where sid = #{sid} and sex = #{sex}")
Student getStudentBySidAndSex(@Param("sid") int sid, @Param("sex") String sex);
注解控制缓存
@CacheNamespace(readWrite = false)
public interface MyMapper {
@Select("select * from student")
@Options(useCache = false)
List<Student> getAllStudent();
Mybatis是半自动框架，SQL语句需要自己写，有一定麻烦，JPA框架这种全自动框架，几乎没有SQL语句！
标签：name,student,int,sex,Student,sid,Mybatis 来源： https://www.cnblogs.com/instore/p/16468467.html
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