MyBatis三种查询方式
1.项目目录
2.EmpSelectMapper.java
package com.atguigu.mapper;
import java.util.Map;
import org.apache.ibatis.annotations.MapKey;
import com.atguigu.bean.Emp;
public interface EmpSelectMapper {
//根据eid查询一个员工信息
Emp getEmpByEid(String eid);
//获取所有的员工数量
Integer getCount();
//以map集合获取一个员工信息
Map<String, Object> getEmpMapByEid(String eid);
//以map集合获取所有员工信息
@MapKey("eid")//设置map的建，因为在查询时传出所有的员工信息，可以把员工信息作为值，但是必须设置键
Map<String, Object> getAllEmpMap();
}
3.EmpSelectMapper.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.atguigu.mapper.EmpSelectMapper">
<!-- //根据eid查询一个员工信息
Emp getEmpByEid(String eid); -->
<select id="getEmpByEid" resultType="Emp">
select eid,ename,age,sex from emp where eid=#{eid}
</select>
<!-- //获取所有的员工数量
Integer getCount(); -->
<select id="getCount" resultType="Integer">
select count(eid) from emp
</select>
<!-- //以map集合获取一个员工信息
Map<String, Object> getEmpMapByEid(String eid); -->
<select id="getEmpMapByEid" resultType="java.util.HashMap">
select eid,ename,age,sex from emp where eid=#{eid}
</select>
<!-- //以map集合获取所有员工信息
@MapKey("eid")//设置map的建，因为在查询时传出所有的员工信息，可以把员工信息作为值，但是必须设置键
Map<String, Object> getAllEmpMap(); -->
<select id="getAllEmpMap" resultType="Emp">
select eid,ename,age,sex from emp
</select>
</mapper>
4.TestSelect.java
package com.atguigu.test;
import java.io.IOException;
import java.io.InputStream;
import java.util.Map;
import javax.annotation.Resource;
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 com.atguigu.bean.Emp;
import com.atguigu.mapper.EmpSelectMapper;
public class TestSelect {
@Test
public void testSelect() throws IOException{
InputStream is = Resources.getResourceAsStream("mybatis-config.xml");
SqlSessionFactory sqlSessionFactory = new SqlSessionFactoryBuilder().build(is);
SqlSession sqlSession = sqlSessionFactory.openSession(true);
EmpSelectMapper mapper = sqlSession.getMapper(EmpSelectMapper.class);
//若查询出的数据有多条，则绝不能将接口中方法的返回值设置为Javabean
// Emp emp = mapper.getEmpByEid("3");
// System.out.println(emp);
//获取员工总记录数
// Integer i = mapper.getCount();
// System.out.println(i);
//以map获取单个emp
// Map<String, Object> map = mapper.getEmpMapByEid("6");
// System.out.println(map);
//以map获取所有emp
Map<String, Object> map = mapper.getAllEmpMap();
System.out.println(map);
}
}
