系列八、Mybatis一对多查询，只查询出了一条记录
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
org.springframework.boot
spring-boot-starter-web
org.springframework.boot
spring-boot-devtools
runtime
true
org.springframework.boot
spring-boot-starter-test
test
org.springframework.boot
spring-boot-starter-security
com.baomidou
mybatis-plus-boot-starter
3.4.1
mysql
mysql-connector-java
8.0.26
com.alibaba
druid-spring-boot-starter
1.1.21
org.projectlombok
lombok
true
junit
junit
4.13.2
test
com.alibaba
fastjson
1.2.76
org.apache.commons
commons-collections4
4.3
org.apache.commons
commons-lang3
3.11
cn.hutool
hutool-all
5.7.22
com.fasterxml.jackson.core
jackson-databind
2.12.1
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 roles;
@Override
public Collection getAuthorities() {
List 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;
}
@Override
public String getUsername() {
return username;
}
public void setPassword(String password) {
this.password = password;
}
@Override
public String getPassword() {
return password;
}
public void setAccountNonExpired(Boolean accountNonExpired) {
this.accountNonExpired = accountNonExpired;
}
@Override
public boolean isAccountNonExpired() {
return accountNonExpired;
}
public void setAccountNonLocked(Boolean accountNonLocked) {
this.accountNonLocked = accountNonLocked;
}
@Override
public boolean isAccountNonLocked() {
return accountNonLocked;
}
public void setCredentialsNonExpired(Boolean credentialsNonExpired) {
this.credentialsNonExpired = credentialsNonExpired;
}
@Override
public boolean isCredentialsNonExpired() {
return credentialsNonExpired;
}
public void setEnabled(Boolean enabled) {
this.enabled = enabled;
}
@Override
public boolean isEnabled() {
return enabled;
}
public List getRoles() {
return roles;
}
public void setRoles(List 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 {
/**
* 根据用户名查询用户
* @param username
* @return
*/
UserDO loadUserByUsername(String username);
} 4.5、UserMapper.xml
五、测试
5.1、Navicat测试（正常）
SELECT
mu.id,
mu.username,
mr.`name`,
mr.name_zh
FROM
mybatis_user mu
LEFT JOIN mybatis_user_role mur ON mu.id = mur.u_id
LEFT JOIN mybatis_role mr ON mr.id = mur.r_id
WHERE
mu.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