一、Mybatis一对多查询，只查询出了一条记录

1.1、问题说明

        典型的权限管理框架的数据库表中，一般会存在这样3种角色的表，即用户表、角色表、用户角色关联表，表设计好之后，往这三张表中初始化了一些测试数据，现在有一个需求通过用户名查询用户的id、username、name、nameZh，在Navicat等工具中查询能够正常查询出来，但是使用mapper去查却只返回一条数据。

二、sql初始化

drop database if exists 20231101_mybatis;
create database 20231101_mybatis;
use 20231101_mybatis;DROP TABLE IF EXISTS `mybatis_user`;
CREATE TABLE `mybatis_user`  (`id` int NOT NULL AUTO_INCREMENT COMMENT '用户编号',`username` varchar(50) CHARACTER SET utf8mb4 COLLATE utf8mb4_0900_ai_ci NULL DEFAULT NULL COMMENT '用户名',`password` varchar(100) CHARACTER SET utf8mb4 COLLATE utf8mb4_0900_ai_ci NULL DEFAULT NULL COMMENT '密码',`account_non_expired` int NOT NULL DEFAULT 1 COMMENT '账户是否没有过期（1：没有过期、0：已过期）',`account_non_locked` int NOT NULL DEFAULT 1 COMMENT '账户是否没有被锁定（1：没有锁定、0：已锁定）',`credentials_non_expired` int NOT NULL DEFAULT 1 COMMENT '密码是否没有过期（1：没有过期、0：已过期）',`enabled` int NOT NULL DEFAULT 1 COMMENT '账户是否可用（1：可用、0：不可用）',PRIMARY KEY (`id`) USING BTREE
) ENGINE = InnoDB CHARACTER SET = utf8mb4 COLLATE = utf8mb4_0900_ai_ci COMMENT = '用户表' ROW_FORMAT = DYNAMIC;INSERT INTO `mybatis_user` VALUES (1, 'root', 'root123',1,1,1,1);
INSERT INTO `mybatis_user` VALUES (2, 'admin', 'admin123',1,1,1,1);
INSERT INTO `mybatis_user` VALUES (3, 'user', 'user123',1,1,1,1);DROP TABLE IF EXISTS `mybatis_role`;
CREATE TABLE `mybatis_role`  (`id` int NOT NULL AUTO_INCREMENT COMMENT '角色编号',`name` varchar(50) CHARACTER SET utf8mb4 COLLATE utf8mb4_0900_ai_ci NULL DEFAULT NULL COMMENT '角色名称（英文）',`name_zh` varchar(50) CHARACTER SET utf8mb4 COLLATE utf8mb4_0900_ai_ci NULL DEFAULT NULL COMMENT '角色名称（中文）',PRIMARY KEY (`id`) USING BTREE
) ENGINE = InnoDB CHARACTER SET = utf8mb4 COLLATE = utf8mb4_0900_ai_ci COMMENT = '角色表' ROW_FORMAT = DYNAMIC;INSERT INTO `mybatis_role` VALUES (1, 'dba', '数据库管理员');
INSERT INTO `mybatis_role` VALUES (2, 'admin', '超级管理员');
INSERT INTO `mybatis_role` VALUES (3, 'user', '用户');DROP TABLE IF EXISTS `mybatis_user_role`;
CREATE TABLE `mybatis_user_role`  (`id` int NOT NULL AUTO_INCREMENT COMMENT '主键',`u_id` int NULL DEFAULT NULL COMMENT '用户ID',`r_id` int NULL DEFAULT NULL COMMENT '角色ID',PRIMARY KEY (`id`) USING BTREE
) ENGINE = InnoDB CHARACTER SET = utf8mb4 COLLATE = utf8mb4_0900_ai_ci COMMENT = '用户角色关联表' ROW_FORMAT = DYNAMIC;INSERT INTO `mybatis_user_role` VALUES (1, 1, 1);
INSERT INTO `mybatis_user_role` VALUES (2, 1, 2);
INSERT INTO `mybatis_user_role` VALUES (3, 2, 2);
INSERT INTO `mybatis_user_role` VALUES (4, 3, 3);

三、表结构

3.1、mybatis_user

3.2、mybatis_role

3.3、mybatis_user_role

四、代码

4.1、pom

<dependencies><!-- spring-boot --><dependency><groupId>org.springframework.boot</groupId><artifactId>spring-boot-starter-web</artifactId></dependency><dependency><groupId>org.springframework.boot</groupId><artifactId>spring-boot-devtools</artifactId><scope>runtime</scope><optional>true</optional></dependency><dependency><groupId>org.springframework.boot</groupId><artifactId>spring-boot-starter-test</artifactId><scope>test</scope></dependency><dependency><groupId>org.springframework.boot</groupId><artifactId>spring-boot-starter-security</artifactId></dependency><!-- 数据源 --><dependency><groupId>com.baomidou</groupId><artifactId>mybatis-plus-boot-starter</artifactId><version>3.4.1</version></dependency><dependency><groupId>mysql</groupId><artifactId>mysql-connector-java</artifactId><version>8.0.26</version></dependency><dependency><groupId>com.alibaba</groupId><artifactId>druid-spring-boot-starter</artifactId><version>1.1.21</version></dependency><!-- 工具 --><dependency><groupId>org.projectlombok</groupId><artifactId>lombok</artifactId><optional>true</optional></dependency><dependency><groupId>junit</groupId><artifactId>junit</artifactId><version>4.13.2</version><scope>test</scope></dependency><dependency><groupId>com.alibaba</groupId><artifactId>fastjson</artifactId><version>1.2.76</version></dependency><dependency><groupId>org.apache.commons</groupId><artifactId>commons-collections4</artifactId><version>4.3</version></dependency><dependency><groupId>org.apache.commons</groupId><artifactId>commons-lang3</artifactId><version>3.11</version></dependency><dependency><groupId>cn.hutool</groupId><artifactId>hutool-all</artifactId><version>5.7.22</version></dependency><dependency><groupId>com.fasterxml.jackson.core</groupId><artifactId>jackson-databind</artifactId><version>2.12.1</version></dependency></dependencies>

4.2、UserDO

@TableName("mybatis_user")
@AllArgsConstructor
@NoArgsConstructor
@Accessors(chain = true)
@ToString
public class UserDO implements UserDetails {/*** 主键*/private Long id;/*** 用户名*/private String username;/*** 密码*/private String password;/*** 账户是否没有过期*/private Boolean accountNonExpired;/*** 账户是否没有被锁定*/private Boolean accountNonLocked;/*** 密码是否没有过期*/private Boolean credentialsNonExpired;/*** 账户是否可用*/private Boolean enabled;/*** 角色*/@TableField(exist = false)private List<RoleDO> roles;@Overridepublic Collection<? extends GrantedAuthority> getAuthorities() {List<SimpleGrantedAuthority> authorities = new ArrayList<>();for (RoleDO role : getRoles()) {authorities.add(new SimpleGrantedAuthority(role.getName()));}return authorities;}public Long getId() {return id;}public void setId(Long id) {this.id = id;}public void setUsername(String username) {this.username = username;}@Overridepublic String getUsername() {return username;}public void setPassword(String password) {this.password = password;}@Overridepublic String getPassword() {return password;}public void setAccountNonExpired(Boolean accountNonExpired) {this.accountNonExpired = accountNonExpired;}@Overridepublic boolean isAccountNonExpired() {return accountNonExpired;}public void setAccountNonLocked(Boolean accountNonLocked) {this.accountNonLocked = accountNonLocked;}@Overridepublic boolean isAccountNonLocked() {return accountNonLocked;}public void setCredentialsNonExpired(Boolean credentialsNonExpired) {this.credentialsNonExpired = credentialsNonExpired;}@Overridepublic boolean isCredentialsNonExpired() {return credentialsNonExpired;}public void setEnabled(Boolean enabled) {this.enabled = enabled;}@Overridepublic boolean isEnabled() {return enabled;}public List<RoleDO> getRoles() {return roles;}public void setRoles(List<RoleDO> roles) {this.roles = roles;}
}

4.3、RoleDO

@TableName("mybatis_role")
@Data
@AllArgsConstructor
@NoArgsConstructor
@Accessors(chain = true)
public class RoleDO implements Serializable {/*** 角色id*/@TableField(value = "rId")private Long id;/*** 角色名称（英文名称）*/private String name;/*** 角色名称（中文名称）*/private String nameZh;}

4.3、UserRoleDO

@TableName("mybatis_user_role")
@Data
@AllArgsConstructor
@NoArgsConstructor
@Accessors(chain = true)
public class UserRoleDO implements Serializable {/*** 主键*/private Long id;/*** 用户id*/private Long uId;/*** 角色id*/private Long rId;}

4.4、UserMapper

public interface UserMapper extends BaseMapper<UserDO> {/*** 根据用户名查询用户* @param username* @return*/UserDO loadUserByUsername(String username);
}

4.5、UserMapper.xml

<!DOCTYPE mapperPUBLIC "-//mybatis.org//DTD Mapper 3.0//EN""http://mybatis.org/dtd/mybatis-3-mapper.dtd"><mapper namespace="org.star.mapper.UserMapper"><resultMap id="BaseResultMap" type="userDO"><id property="id" column="id"/><result property="username" column="username"/><result property="password" column="password"/><result property="accountNonExpired" column="account_non_expired"/><result property="accountNonLocked" column="account_non_locked"/><result property="credentialsNonExpired" column="credentials_non_expired"/><result property="enabled" column="enabled"/><collection property="roles" ofType="roleDO"><id property="id" column="id"/><result property="name" column="name"/><result property="nameZh" column="name_zh"/></collection></resultMap><select id="loadUserByUsername" resultMap="BaseResultMap">select mu.id, mu.username, mr.`name`, mr.name_zh,mr.idfrom mybatis_user muleft join mybatis_user_role mur on mu.id = mur.u_idleft join mybatis_role mr on mr.id = mur.r_idwhere mu.username = #{username}</select></mapper>

五、测试

5.1、Navicat测试（正常）

SELECTmu.id,mu.username,mr.`name`,mr.name_zh 
FROMmybatis_user muLEFT JOIN mybatis_user_role mur ON mu.id = mur.u_idLEFT JOIN mybatis_role mr ON mr.id = mur.r_id 
WHEREmu.username = 'root'

5.2、代码测试（异常）

        同样的查询条件，Navicat中查询正常，代码中查询不正常，原因是什么呢？ 多条的数据只显示一条，是因为字段名相同，两张表的主键都是id，就只会显示一条数据，只需要把多条数据的表id的column修改成别名就可以了。如下所示：

5.3、问题解决

5.3.1、修改UserMapper.xml的映射信息和查询信息

5.3.2、再次查询（正常） 

六、参考 

https://www.cnblogs.com/damugua/p/17046724.html