mybatis
Mybatis 单表CURD细节
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${} 与#{} 区别(面试题)
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${} 拼接sql 造成sql注入 #{} 使用?占位
如果作为值, 推荐使用#{}
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${} 实现一些动态排序,使用
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#{column}
select * from tb_userinfo order by ? desc
column: id 赋值
sql: select * from tb_userinfo order by 'id' desc
根据 'id'常数列排序
结果:
[User{name='张三丰', gender='男', age=108, address='湖北', email='zhangsanfeng@163.com', qq='123456'}, User{name='李思琪', gender='女', age=21, address='上海', email='lisiqi@163.com', qq='12312321'}, User{name='李思思', gender='女', age=21, address='北京', email='lisisi@126.com', qq='3323422'}, User{name='李大海', gender='男', age=22, address='上海', email='lidahai@ss.com', qq='12212121'}, User{name='倪大红', gender='女', age=23, address='上海', email='asdsa@ss.com', qq='12312321'}, User{name='fsdsf', gender='男', age=43, address='北京', email='aadda@ww.com', qq='544554'}, User{name='wangwu', gender='女', age=18, address='上海', email='wangwu@163.com', qq='21321321'}, User{name='李四', gender='男', age=21, address='湖南', email='lisi@163.com', qq='222222'}, User{name='zhangsansan', gender='男', age=21, address='湖南', email='zhangsansan@163.com', qq='12321312'}, User{name='莫问归期', gender='女', age=21, address='北京', email='1234567@qq.com', qq='1234567'}, User{name='一个人挺好', gender='男', age=21, address='北京', email='sadsad@163.com', qq='2313128'}, User{name='张三', gender='男', age=21, address='长沙', email='zhangsan@qq.com', qq='1234678'}, User{name='张三', gender='男', age=21, address='长沙', email='zhangsan@qq.com', qq='1234678'}]
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resultType: 不是表示方法的返回值类型, 查询到结果集中记录映射到java那个实体类, 写的实体类
too many paramNumber selectone所带所导致的结果
先后顺序：(先执行插入操作，再执行这个查询生成id的命令)
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selectOne() 与selectList() 区别
selectOne() 查询结果集最多有一行记录, 超出一行记录, 抛异常 TooManyResultsException
selectList(): 查询结果集可以0 ,1 , 多条 返回的List<T>, 可以使用selectList() 替换selectOne()
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插入操作,
mysql提供: select LAST_INSERT_ID(); 查找生成id值
只能获取当前会话执行插入操作的产生的id
Mybatis的Dao层开发模式
1. 传统的Dao模式
编写一个Dao接口, 提供Dao实现类
package com.fs.dao;
import com.fs.entity.User;
import java.util.List;
public interface UserDao {
/**
* 根据主键查询
* @param id
* @return
*/
User selectById(Integer id);
/**
* 查询所有
* @return
*/
List<User> selectAll();
/**
* 添加
* @param user
* @return
*/
int insert(User user);
/**
* 根据主键删除
* @param id
* @return
*/
int deleteById(Integer id);
/**
* 根据主键修改
* @param user
* @return
*/
int updateById(User user);
}
package com.fs.dao.impl;
import com.fs.dao.UserDao;
import com.fs.entity.User;
import com.fs.util.MybatisUtil;
import org.apache.ibatis.session.SqlSession;
import java.util.List;
public class UserDaoImpl implements UserDao {
private SqlSession sqlSession;
public UserDaoImpl() {
this.sqlSession = MybatisUtil.getSqlSession();
}
@Override
public User selectById(Integer id) {
User user = sqlSession.selectOne("UserDao.selectById",id);
sqlSession.close();
return user;
}
@Override
public List<User> selectAll() {
List<User> users = sqlSession.selectList("UserDao.selectAll");
sqlSession.close();
return users;
}
@Override
public int insert(User user) {
int row = sqlSession.insert("UserDao.addUser",user);
//提交事务
sqlSession.commit();
sqlSession.close();
return row;
}
@Override
public int deleteById(Integer id) {
int row = sqlSession.delete("UserDao.deleteById", id);
sqlSession.commit();
sqlSession.close();
return row;
}
@Override
public int updateById(User user) {
return 0;
}
}
传统Dao方式问题:
重复代码重复写
StatementId硬编码方式,
产生原因: Dao的实现类
2. Mapper代理模式 重点
Mybatis推荐,
编写Dao接口,不需要编写实现类, 由Mybatis动态代理自动生成的实现类对象
为了区分传统Dao方式, 把Dao 取名为Mapper 层: Mapper 接口 UserMapper
使用Mapper代理模式前提条件:
Sql映射文件的要求:
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namespace必须写成Mapper接口全限定名
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statement的id写成方法名
package com.fs.mapper;
import com.fs.entity.User;
import java.util.List;
public interface UserMapper {
/**
* 根据主键查询
* @param id
* @return
*/
User selectById(Integer id);
/**
* 查询所有
* @return
*/
List<User> selectAll();
/**
* 添加
* @param user
* @return
*/
int insert(User user);
/**
* 根据主键删除
* @param id
* @return
*/
int deleteById(Integer id);
/**
* 根据主键修改
* @param user
* @return
*/
int updateById(User user);
}
sql映射文件:
<?xml version="1.0" encoding="UTF-8" ?>
<!DOCTYPE mapper
PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN"
"https://mybatis.org/dtd/mybatis-3-mapper.dtd">
<mapper namespace="com.fs.mapper.UserMapper">
<select id="selectById" parameterType="int" resultType="com.fs.entity.User">
select * from tb_userinfo where id = #{id}
</select>
<delete id="deleteById" parameterType="int">
delete from tb_userinfo where id = #{id}
</delete>
<select id="selectAll" resultType="com.fs.entity.User">
select * from tb_userinfo
</select>
<insert id="insert" parameterType="com.fs.entity.User">
<selectKey resultType="int" order="AFTER" keyProperty="id">
select LAST_INSERT_ID()
</selectKey>
insert into tb_userinfo(name,gender,age,address,email,qq,photo) values(#{name},
#{gender},#{age},#{address},#{email},#{qq},#{photo})
</insert>
</mapper>
