Mybatis查询到数据但是返回结果为null-蒲公英云

Mybatis查询到数据但是返回结果为null

问题描述：
查看控制台打印的日志
在这里插入图片描述
可以看出执行了sql语句，但是也查询到了2条记录，但是返回的结果为null，说明没有设置成功数据
代码:
Position.java

public class Position implements Serializable { 
    @Id
// @GeneratedValue(strategy = GenerationType.IDENTITY)
    @Column(name = "position_id")
    private Integer id;
    @Column(name = "position_name", length = 15)
    private String name;
  }

PositionMapper.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="org.lieying.dao.PositionMapper">
    <select id="selectPositionByPositionCategoryId" resultType="Position" parameterType="int">
        select * from position where position_category_id = #{position_category_id}
    </select>
</mapper>

原因:
由于java的字段名称和数据库的字段名称不一致，所有set方法无法设置成功数据
解决方法:
（1）使用sql语句修改字段名称
即

<select id="selectPositionByPositionCategoryId" resultType="Position" parameterType="int">
    select position_id as id,position_name as name from position where position_category_id = #{position_category_id}
    </select>

在这里插入图片描述
成功查询到数据

(2)在配置文件中配置resultMap映射数据库属性和java类属性，设置select的返回类型为resultMap的id，即

<select id="selectPositionByPositionCategoryId" resultMap="positionResultMap" parameterType="int">
 --select position_id as id,position_name as name from position 
    select position_id as id,position_name as name from position where position_category_id = #{position_category_id}
    </select>
    <resultMap id="positionResultMap" type="Position">
        <id column="position_id" property="id"/>
        <result column="position_name" property="name"/>
        <result column="position_address" property="address"/>
    </resultMap>