Cause: org.apache.ibatis.ognl.OgnlException: source is null for getProperty(null, \“wname\“)\r\n\ta

完整的报错是这样的：

“error”: “Internal Server Error”,
“trace”: "org.mybatis.spring.MyBatisSystemException: nested exception is org.apache.ibatis.builder.BuilderException: Error evaluating expression ‘checkin.adminVo.wname != null and checkin.adminVo.wname != ‘’’. Cause: org.apache.ibatis.ognl.OgnlException: source is null for getProperty(null, “wname”)\r\n\tat

我们使用mybatis编写动态sql的时候，可能会遇到这种场景，在实体类中包含了实体类：

/*
 * @author 小爽帅到拖网速
 * @since 2021-11-17
 */
@Data
@EqualsAndHashCode(callSuper = false)
@Accessors(chain = true)
@TableName("t_checkin")
@ApiModel(value="Checkin对象", description="")
public class Checkin implements Serializable {

    @ApiModelProperty(value = "学生")
    @TableField(exist = false)
    private StudentVo studentVo;

    @ApiModelProperty(value = "员工")
    @TableField(exist = false)
    private AdminVo adminVo;

}

在写动态sql 的时候，势必会运用到实体类中实体类的属性，我上面的报错是因为我在mapper.xml中的动态sql是这样写的

 <if test="checkin.studentVo.gender != null and checkin.studentVo.gender != ''">
      and s.gender = #{checkin.studentVo.gender,jdbcType=VARCHAR}
  if>
<if test="checkin.adminVo.wname != null and checkin.adminVo.wname != ''">
    and a.wname like concat('%', #{checkin.adminVo.wname,jdbcType=VARCHAR})
if>
          

如果动态sql这么写了，参数studentVo为空的时候gender势必也为空，所以我们不能够去这么写

正确代码：

<if test="checkin.studentVo != null">
  <if test="checkin.studentVo.gender != null and checkin.studentVo.gender != ''">
      and s.gender = #{checkin.studentVo.gender,jdbcType=VARCHAR}
  </if>
</if>
<if test="checkin.adminVo != null">
  <if test="checkin.adminVo.wname != null and checkin.adminVo.wname != ''">
      and a.wname like concat('%', #{checkin.adminVo.wname,jdbcType=VARCHAR})
  </if>
</if>

多加一层判断实体类是否为空即可！