无废话mybatis三(select的用法)

UserMapper.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="tk.mybatis.simple.mapper.UserMapper">
    <resultMap id="userMap" type="SysUser">
        <id property="id" column="id"/>
        <result property="userName" column="user_Name"/>
        <result property="userPassword" column="userPassword"/>
        <result property="userEmail" column="userEmail"/>
        <result property="userInfo" column="userInfo"/>
        <result property="headImg" column="headImg" jdbcType="BLOB"/>
        <result property="createTime" column="createTime" jdbcType="TIMESTAMP"/>
    </resultMap>

    <select id="selectByid" resultMap="userMap">
        select * from sys_user where id =#{id}
    </select>

    <select id="selectAll" resultType="tk.mybatis.simple.model.SysUser">
        select * from sys_user
    </select>
</mapper>

mapper节点中需要指定namespace="tk.mybatis.simple.mapper.UserMapper"

resultMap:用于设置返回值的类型和映射关系
<select> : 映射查询语句使用的标签。
id ：命名空间中的唯 标识符，可用来代表这条语句。
'# {id} :MyBatis SQL 中使用预编译参数的一种方式，大括号中的 id 是传入的参数名

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如果传入的是实体类那必须和实体类中字段一致才行,否则报错

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result: 列结果

resultMap节点中的result标签 property表示java属性, column表示数据库字段, jdbcType表示列对应的数据库类型。在下面两个select标签, 一个是根据用户id查询用户,其返回值就是resultMap映射

<select id="selectByid" resultMap="userMap">
        select * from sys_user where id =#{id}
</select>

下面一个是根据设置mybatis的自动映射字段成

<select id="selectAll" resultType="SysUser">
        select * from sys_user
</select>

BaseMapperTest.java

package simple;

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.BeforeClass;

import java.io.IOException;
import java.io.Reader;

public class BaseMapperTest {
    private static SqlSessionFactory sqlSessionFactory;

    @BeforeClass
    public static void init() {
        try {
            Reader reader = Resources.getResourceAsReader("mybatis-config.xml");
            sqlSessionFactory = new SqlSessionFactoryBuilder().build(reader);
            reader.close();
        } catch (IOException ignore) {
            ignore.printStackTrace();
        }
    }

    public SqlSession getSqlSession() {
        return sqlSessionFactory.openSession();
    }
}

@Test
    public void testUserSelectById() {
        SqlSession sqlSession = getSqlSession();
        try {
            SysUser sysUser = sqlSession.selectOne("tk.mybatis.simple.mapper.UserMapper.selectByid", 1);
            System.out.println(sysUser.getUserName());
        } finally {
            sqlSession.close();
        }
    }

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在调用的时候是直接指定名称, 当然还有一种不需要指定名称的方式, 那就是getMapper的方式

@Test
    public void testUserSelectById2() {
        SqlSession sqlSession = getSqlSession();
        try {
            UserMapper userMapper = sqlSession.getMapper(UserMapper.class);
            SysUser sysUser = userMapper.selectByid(Long.valueOf(1));
            System.out.println(sysUser.getUserName());
        } finally {
            sqlSession.close();
        }
    }

    @Test
    public void testUserSelectAll2() {
        SqlSession sqlSession = getSqlSession();
        try {
            UserMapper userMapper = sqlSession.getMapper(UserMapper.class);
            List<SysUser> sysUsers = userMapper.selectAll();
            if (sysUsers != null) {
                for (SysUser user : sysUsers) {
                    System.out.println(user.getUserName());
                }
            }
        } finally {
            sqlSession.close();
        }
    }