1 分页
在学习mybatis等持久层框架的时候,会经常对数据进行增删改查操作,使用最多的是对数据库进行查询操作,如果查询大量数据的时候,我们往往使用分页进行查询,也就是每次处理小部分数据,这样对数据库压力就在可控范围内。
SELECT* from user limit startIndex,pageSize
// 分页
List<User>getUserByLimit(Map<String, Integer> map);
<?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.zs.mapper.UserMapper"><!--结果集映射--><resultMap id="UserMap" type="user"><!--column数据库中的字段,property实体类中的属性--><result column="id" property="id"></result><result column="name" property="name"></result><result column="pwd" property="password"></result></resultMap><select id="getUserByLimit" parameterType="map" resultMap="UserMap">
SELECT* FROM mybatis_user LIMIT #{startIndex},#{pageSize}</select></mapper>
@TestpublicvoidgetUserByLimit(){try(SqlSession sqlSesion= MyBatisUtils.getSqlSesion();){
UserMapper mapper= sqlSesion.getMapper(UserMapper.class);
Map<String, Integer> map=newHashMap<>();
map.put("startIndex",0);
map.put("pageSize",2);
List<User> userList= mapper.getUserByLimit(map);
System.out.println(userList);}}
2 利用注解开发
1、我们在我们的接口中添加注解
//根据查询全部用户@Select("select * from user")
List<User>getUsers();
2、在mybatis的核心配置文件中注入
<!-- 绑定接口--><mappers><mapperclass="com.xxxx.dao.UserMapper"/></mappers>
3、我们去进行测试
@Testpublicvoidtest(){try(SqlSession sqlSession= MyBatisUtils.getSqlSesion();){
UserMapper mapper= sqlSession.getMapper(UserMapper.class);
List<User> users= mapper.getUsers();for(User user:users){
System.out.println(user);}}}
自动提交事务:
publicinterfaceUserMapper{//根据查询全部用户@Select("select * from user")
List<User>getUsers();// 方法存在多个参数,所有的参数前面必须加上@Param@Select("select * from user where id = #{id}")
UsergetUserById(@Param("id")int id);@Insert("insert into user(id,name,pwd) values(#{id},#{name},#{pwd})")intaddUser(User user);@Update("update user set name = #{name} , pwd = #{pwd} where id = #{id}")intupdateUser(User user);@Delete("delete from user where id = #{uid}")intdeleteUser(@Param("uid")int id);}
一定要注意:将接口注册绑定到我们的核心配置文件中:
<!-- 绑定接口--><mappers><mapperclass="com.xxxx.dao.UserMapper"/></mappers>