关于mybatis传入参数一直为null的问题关于mybatis传入参数一直为nul

mybatis传入参数一直为null
mybatis字段为null的解决

先讲一讲sql语句和ResultMap的顺序
实体类UserInfo
UserMapper.xml错误代码
正确写法

mybatis传入参数一直为null 1.配置方面都对的情况下，考虑连接数据库的时候是否设置了编码为utf-8，如果没设置，数据库传过来的时候有可能就是乱码，就会一直是null。
2.有可能是字段名与实体不匹配。
3.可能是有空格问题

mybatis字段为null的解决今天在写项目的mapper.xml文件的时候，出现了个别字段查询结果为null的情况，但sql语句没有错误，仔细查看了一遍，才发现错误，现在记录下来

先讲一讲sql语句和ResultMap的顺序
首先会执行sql语句，sql语句返回字段信息，然后才是ResultMap映射字段信息。

实体类UserInfo

package com.school.oauth.endpoint.domain; import com.fasterxml.jackson.annotation.JsonFormat; import com.fasterxml.jackson.annotation.JsonIgnore; import com.school.parent.domain.BaseDomain; import io.swagger.annotations.ApiModel; import io.swagger.annotations.ApiModelProperty; import lombok.Data; import org.apache.ibatis.annotations.Insert; import org.apache.ibatis.annotations.Update; import org.hibernate.validator.constraints.Length; import org.springframework.format.annotation.DateTimeFormat; import javax.persistence.*; import javax.validation.constraints.Email; import javax.validation.constraints.NotBlank; import javax.validation.constraints.NotNull; import javax.validation.constraints.Pattern; import java.time.ZonedDateTime; import java.util.Date; import java.util.List; @Table(name = "oauth_user")@ApiModel(value = "https://www.it610.com/article/用户表")@Datapublic class UserInfo extends BaseDomain {@Id@GeneratedValue(generator = "JDBC")@ApiModelProperty(value = "https://www.it610.com/article/用户主键，提供给其他表做外键")private Long userId; @Column(unique = true)@NotBlank@Length(max = 32)@ApiModelProperty(value = "https://www.it610.com/article/用户名，必须唯一")private String username; @NotBlank@Length(max = 32)@ApiModelProperty(value = "https://www.it610.com/article/昵称，可以重复")private String nickname; @Length(max = 128)@ApiModelProperty(value = "https://www.it610.com/article/加密密码")private String encryptedPassword; @Length(max = 32)@Pattern(regexp = "^[1][3,4,5,7,8][0-9]{9}$",message = "手机号码格式错误")@ApiModelProperty(value = "https://www.it610.com/article/用户手机号码")private String phone; @Email@Length(max = 128)@ApiModelProperty(value = "https://www.it610.com/article/用户邮箱")private String email; @Length(max = 8)@ApiModelProperty(value = "https://www.it610.com/article/国际冠码，默认 +86")private String idd; @Length(max = 16)@ApiModelProperty(value = "https://www.it610.com/article/性别：男/女")private String gender; @Length(max = 1024)@ApiModelProperty(value = "https://www.it610.com/article/头像地址")private String avatar; @NotBlank@Length(max = 128)@ApiModelProperty(value = "https://www.it610.com/article/所属学校")private String school; @DateTimeFormat(pattern = "yyyy-MM-dd hh:mm:ss")@JsonFormat(pattern = "yyyy-MM-dd hh:mm:ss")@ApiModelProperty(value = "https://www.it610.com/article/账户过期时间")private Date accountExpiredTime; @DateTimeFormat(pattern = "yyyy-MM-dd hh:mm:ss")@JsonFormat(pattern = "yyyy-MM-dd hh:mm:ss")@ApiModelProperty(value = "https://www.it610.com/article/账户锁定时间")private Date accountLockedTime; @DateTimeFormat(pattern = "yyyy-MM-dd hh:mm:ss")@JsonFormat(pattern = "yyyy-MM-dd hh:mm:ss")@ApiModelProperty(value = "https://www.it610.com/article/凭证过期时间")private Date credentialsExpiredTime; @Column(name = "is_admin")@ApiModelProperty(value = "https://www.it610.com/article/是否是管理员")private Boolean admin; @Column(name = "is_able")@ApiModelProperty(value = "https://www.it610.com/article/账户是否启用")private Boolean able; @Length(max = 32)@NotBlank(groups = Insert.class)@ApiModelProperty(value = "https://www.it610.com/article/用户注册平台：WEB(默认)/AliPay/WeChat")private String userType; @Length(max = 64)@ApiModelProperty(value = "https://www.it610.com/article/微信用户识别ID")private String weChatUserId; @Length(max = 64)@ApiModelProperty(value = "https://www.it610.com/article/支付宝用户识别ID")private String aliPayUserId; @Transient@NotBlank(groups = Insert.class)@ApiModelProperty(value = "https://www.it610.com/article/密码")private String password; /*** 一个用户只能对应一个角色（最高权限角色）*/@Transient@ApiModelProperty(value = "https://www.it610.com/article/用户角色集合：guest/user/admin")private List roleList; public UserInfo() {}}

UserMapper.xml错误代码

SELECTu.user_id,u.username,u.nickname,u.encrypted_password,u.phone,u.email,u.idd,u.gender,u.avatar,u.school,u.account_expired_time,u.account_locked_time,u.credentials_expired_time,u.is_admin AS admin,u.is_able AS able,u.user_type,u.we_chat_user_id,u.ali_pay_user_idFROM oauth_user uWHERE u.username = #{username}

这样查询出来的User对象的admin和able字段为空。这是因为我们的selectByUsername 引用了我们定义的ResultMap。
注意看sql语句，其中有两个字段我们取了别名

u.is_admin AS admin,u.is_able AS able,

也就是说，当sql语句查询出来的is_admin字段和is_able 字段已经变为了admin字段和able字段，而ResultMap里面这两个字段的映射：

当ResultMap去映射字段信息的时候，发现找不到is_admin字段和is_able字段，因为在sql语句我们已经为这两个字段去了别名，现在这两个字段叫admin和able。所有ResultMap映射到实体类的时候，就会出现这两个字段为空的情况。
【关于mybatis传入参数一直为null的问题】
正确写法
去掉sql语句里面的别名，就可以咯。这样resultMap就可以找到相应的字段了。

SELECTu.user_id,u.username,u.nickname,u.encrypted_password,u.phone,u.email,u.idd,u.gender,u.avatar,u.school,u.account_expired_time,u.account_locked_time,u.credentials_expired_time,u.is_admin,u.is_able,u.user_type,u.we_chat_user_id,u.ali_pay_user_idFROM oauth_user uWHERE u.username = #{username}

以上为个人经验，希望能给大家一个参考，也希望大家多多支持脚本之家。