Mybatis-Plus用纯注解搞定一对多查询

业务中很常见的用户-角色就属于典型的一对多关系. 假设我们需要将用户信息（包括了用户对应的角色信息）查询出来

数据表结构

user表和role表的关系为多对多，即一个user可以分配多个role，一个role可以属于多个user。

1.user表

CREATE TABLE `user` (
  `id` int(11) NOT NULL AUTO_INCREMENT COMMENT '主键',
  `nickname` varchar(20) NOT NULL COMMENT '昵称',
  `birthday` date NOT NULL COMMENT '生日',
  `username` varchar(32) NOT NULL COMMENT '用户名',
  `password` varchar(30) NOT NULL COMMENT '密码',
  `status` varchar(2) NOT NULL DEFAULT '0' COMMENT '状态 ',
  `create_time` datetime NOT NULL DEFAULT CURRENT_TIMESTAMP COMMENT '创建时间',
  `update_time` datetime NOT NULL DEFAULT CURRENT_TIMESTAMP ON UPDATE CURRENT_TIMESTAMP COMMENT '更新时间',
  PRIMARY KEY (`id`) USING BTREE
) ENGINE=InnoDB;

INSERT INTO `user` VALUES (1, 'lh', '2022-06-29', '李大', '123456', '0', '2022-06-29 09:02:07', '2022-06-29 09:02:07');
INSERT INTO `user` VALUES (2, 'ww', '2022-06-29', '陈大', '123456', '0', '2022-06-29 13:06:24', '2022-06-29 13:06:24');
INSERT INTO `user` VALUES (3, 'aa', '2022-06-29', '刘达', '123456', '0', '2022-06-29 13:06:48', '2022-06-29 13:06:48');

2.role表

CREATE TABLE `role` (
  `id` int(11) NOT NULL AUTO_INCREMENT COMMENT '主键id',
  `name` varchar(20) NOT NULL COMMENT '角色名称',
  `remark` varchar(50) DEFAULT NULL COMMENT '角色描述',
  PRIMARY KEY (`id`) USING BTREE
) ENGINE=InnoDB;

INSERT INTO `role` VALUES (1, '系统管理员', '系统管理员');
INSERT INTO `role` VALUES (2, '数据管理员', '数据管理员');

3.user_role中间表

CREATE TABLE `user_role` (
  `user_id` int(11) NOT NULL COMMENT '用户id',
  `role_id` int(11) DEFAULT NULL COMMENT '角色id'
) ENGINE=InnoDB;

INSERT INTO `user_role` VALUES (1, 1);
INSERT INTO `user_role` VALUES (1, 2);
INSERT INTO `user_role` VALUES (2, 1);
INSERT INTO `user_role` VALUES (2, 2);
INSERT INTO `user_role` VALUES (3, 1);

实体类:

1.User类:

package wjw.test.mybatisplus.vo;

import java.io.Serializable;
import java.time.LocalDate;
import java.time.LocalDateTime;

import com.baomidou.mybatisplus.annotation.IdType;
import com.baomidou.mybatisplus.annotation.TableId;

public class User implements Serializable {

  private static final long serialVersionUID = 1L;

  @TableId(
      type = IdType.AUTO)
  /**
   * 主键
   */
  private Integer id;

  /**
   * 昵称
   */
  private String nickname;

  /**
   * 生日
   */
  private LocalDate birthday;

  /**
   * 用户名
   */
  private String username;

  /**
   * 密码
   */
  private String password;

  /**
   * 状态
   */
  private String status;

  /**
   * 创建时间
   */
  private LocalDateTime createTime;

  /**
   * 更新时间
   */
  private LocalDateTime updateTime;

  public User() {
  }

  public Integer getId() {
    return id;
  }

  public void setId(Integer id) {
    this.id = id;
  }

  public String getNickname() {
    return nickname;
  }

  public void setNickname(String nickname) {
    this.nickname = nickname;
  }

  public LocalDate getBirthday() {
    return birthday;
  }

  public void setBirthday(LocalDate birthday) {
    this.birthday = birthday;
  }

  public String getUsername() {
    return username;
  }

  public void setUsername(String username) {
    this.username = username;
  }

  public String getPassword() {
    return password;
  }

  public void setPassword(String password) {
    this.password = password;
  }

  public String getStatus() {
    return status;
  }

  public void setStatus(String status) {
    this.status = status;
  }

  public LocalDateTime getCreateTime() {
    return createTime;
  }

  public void setCreateTime(LocalDateTime createTime) {
    this.createTime = createTime;
  }

  public LocalDateTime getUpdateTime() {
    return updateTime;
  }

  public void setUpdateTime(LocalDateTime updateTime) {
    this.updateTime = updateTime;
  }

  @Override
  public String toString() {
    StringBuilder builder = new StringBuilder();
    builder.append("User [id=");
    builder.append(id);
    builder.append(", nickname=");
    builder.append(nickname);
    builder.append(", birthday=");
    builder.append(birthday);
    builder.append(", username=");
    builder.append(username);
    builder.append(", password=");
    builder.append(password);
    builder.append(", status=");
    builder.append(status);
    builder.append(", createTime=");
    builder.append(createTime);
    builder.append(", updateTime=");
    builder.append(updateTime);
    builder.append("]");
    return builder.toString();
  }

}

2.Role类:

package wjw.test.mybatisplus.vo;

import java.io.Serializable;

import com.baomidou.mybatisplus.annotation.IdType;
import com.baomidou.mybatisplus.annotation.TableId;

public class Role implements Serializable {

  private static final long serialVersionUID = 1L;

  @TableId(
      type = IdType.AUTO)
  /**
   * 主键id
   */
  private Integer id;

  /**
   * 角色名称
   */
  private String name;

  /**
   * 角色描述
   */
  private String remark;

  public Role() {
  }

  public Integer getId() {
    return id;
  }

  public void setId(Integer id) {
    this.id = id;
  }

  public String getName() {
    return name;
  }

  public void setName(String name) {
    this.name = name;
  }

  public String getRemark() {
    return remark;
  }

  public void setRemark(String remark) {
    this.remark = remark;
  }

  @Override
  public String toString() {
    StringBuilder builder = new StringBuilder();
    builder.append("Role [id=");
    builder.append(id);
    builder.append(", name=");
    builder.append(name);
    builder.append(", remark=");
    builder.append(remark);
    builder.append("]");
    return builder.toString();
  }

}

3.包含一对多关系的UserVo类:

package wjw.test.mybatisplus.vo;

import java.time.LocalDate;
import java.util.List;

public class UserVo {
  /**
   * 用户编号
   */
  private Integer id;

  /**
   * 昵称
   */
  private String nick_Name;

  /**
   * 用户名
   */
  private String username;

  /**
   * 生日
   */
  private LocalDate birthday;

  private List<Role> roles;

  public Integer getId() {
    return id;
  }

  public void setId(Integer id) {
    this.id = id;
  }

  public String getNick_Name() {
    return nick_Name;
  }

  public void setNick_Name(String nick_Name) {
    this.nick_Name = nick_Name;
  }

  public String getUsername() {
    return username;
  }

  public void setUsername(String username) {
    this.username = username;
  }

  public LocalDate getBirthday() {
    return birthday;
  }

  public void setBirthday(LocalDate birthday) {
    this.birthday = birthday;
  }

  public List<Role> getRoles() {
    return roles;
  }

  public void setRoles(List<Role> roles) {
    this.roles = roles;
  }

  public UserVo() {
    super();
  }

  @Override
  public String toString() {
    StringBuilder builder = new StringBuilder();
    builder.append("UserVo [id=");
    builder.append(id);
    builder.append(", nick_Name=");
    builder.append(nick_Name);
    builder.append(", username=");
    builder.append(username);
    builder.append(", birthday=");
    builder.append(birthday);
    builder.append(", roles=");
    builder.append(roles);
    builder.append("]");
    return builder.toString();
  }

}

Mapper类:

1.RoleMapper:

package wjw.test.mybatisplus.mapper;

import java.util.List;

import org.apache.ibatis.annotations.Mapper;
import org.apache.ibatis.annotations.Select;

import com.baomidou.mybatisplus.core.mapper.BaseMapper;

import wjw.test.mybatisplus.vo.Role;

@Mapper
public interface RoleMapper extends BaseMapper<Role> {
    /**
     * 根据指定的userId去user和user_role关联表查出该user所属role列表
     * @param userId
     * @return
   */
  @Select("select * from role left join user_role on role.id=user_role.role_id where user_role.user_id=#{userId}")
  List<Role> getListByUserId(Integer userId);    
}

2.UserMapper:

package wjw.test.mybatisplus.mapper;

import java.util.List;

import org.apache.ibatis.annotations.Many;
import org.apache.ibatis.annotations.Mapper;
import org.apache.ibatis.annotations.Param;
import org.apache.ibatis.annotations.Result;
import org.apache.ibatis.annotations.Results;
import org.apache.ibatis.annotations.Select;

import com.baomidou.mybatisplus.core.conditions.query.QueryWrapper;
import com.baomidou.mybatisplus.core.mapper.BaseMapper;

import wjw.test.mybatisplus.vo.User;
import wjw.test.mybatisplus.vo.UserVo;

@Mapper
public interface UserMapper extends BaseMapper<User> {
    //OneToMany一对多查询
    @Select("select * from user where ${ew.sqlSegment}")
    @Results({@Result(column = "id",property = "id"),                         // <1>
              @Result(column = "nickname",property = "nick_Name"),
              @Result(column = "id" /* 这里的id是要传递给下面查询里需要的参数 */,   //<2>
                      property = "roles" /* 这里是UserVo类里的roles字段 */,many=@Many(
                      select = "wjw.test.mybatisplus.mapper.RoleMapper.getListByUserId"
              ))
    })
    List<UserVo> getList(@Param("ew") QueryWrapper wrapper);    
}

<1>: @Result(column=“id”,property=“Id”),这个可以不写，也不会报错，但是会导致我们查询结果列表里每个UVO 实体的Id等属性没有值。

<2>: 这个@Result中

column代表子查询关联的主表中的列名，即子查询和主查询之间的关联关系。

property，代表子查询的查询结果关联的实体属性，就是UserVo中的roles字段。

select="wjw.test.mybatisplus.mapper.RoleMapper.getListByUserId"代表使用的子查询方法，就是RoleMapper类里的getListByUserId()方法。 意思就是查询主表，并将主表的id这个列和子查询关联起来，将id的值作为查询条件传入子查询中，子查询返回的结果存入到属性roles中.

测试

package wjw.test.mybatisplus;

import java.util.List;

import org.junit.jupiter.api.AfterEach;
import org.junit.jupiter.api.BeforeEach;
import org.junit.jupiter.api.Test;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.boot.test.context.SpringBootTest;
import org.springframework.boot.test.context.SpringBootTest.WebEnvironment;
import org.springframework.test.context.ActiveProfiles;

import com.baomidou.mybatisplus.core.conditions.query.QueryWrapper;

import wjw.test.mybatisplus.mapper.RoleMapper;
import wjw.test.mybatisplus.mapper.UserMapper;
import wjw.test.mybatisplus.vo.User;
import wjw.test.mybatisplus.vo.UserVo;

@SpringBootTest(webEnvironment = WebEnvironment.NONE)
public class MybatisPlusTests1 {
  @Autowired
  private UserMapper userMapper;

  @Autowired
  private RoleMapper roleMapper;

  public MybatisPlusTests1() {
    //
  }

  @BeforeEach
  public void setup() {
    //
  }

  @AfterEach
  public void stop() {
  }

  @Test
  public void getUserInfo(){
      QueryWrapper<User> wrapper=new QueryWrapper();
      wrapper.in("id",1,2);
      List<UserVo> list = userMapper.getList(wrapper);
      System.out.println(list);
  }
  
}

输出结果:

wjw.test.mybatisplus.MybatisPlusTests1 - [logStarted,61] - Started MybatisPlusTests1 in 2.855 seconds (JVM running for 3.885)
wjw.test.mybatisplus.mapper.UserMapper.getList - [debug,137] - ==>  Preparing: select * from user where (id IN (?,?))
wjw.test.mybatisplus.mapper.UserMapper.getList - [debug,137] - ==> Parameters: 1(Integer), 2(Integer)
wjw.test.mybatisplus.mapper.UserMapper.getList - [trace,143] - <==    Columns: id, nickname, birthday, username, password, status, create_time, update_time
wjw.test.mybatisplus.mapper.UserMapper.getList - [trace,143] - <==        Row: 1, lh, 2022-06-29, 李大, 123456, 0, 2022-06-29 09:02:07.0, 2022-06-29 09:02:07.0
w.t.mybatisplus.mapper.RoleMapper.getListByUserId - [debug,137] - ====>  Preparing: select * from role left join user_role on role.id=user_role.role_id where user_role.user_id=?
w.t.mybatisplus.mapper.RoleMapper.getListByUserId - [debug,137] - ====> Parameters: 1(Integer)
w.t.mybatisplus.mapper.RoleMapper.getListByUserId - [trace,143] - <====    Columns: id, name, remark, user_id, role_id
w.t.mybatisplus.mapper.RoleMapper.getListByUserId - [trace,143] - <====        Row: 1, 系统管理员, 系统管理员, 1, 1
w.t.mybatisplus.mapper.RoleMapper.getListByUserId - [trace,143] - <====        Row: 2, 数据管理员, 数据管理员, 1, 2
w.t.mybatisplus.mapper.RoleMapper.getListByUserId - [debug,137] - <====      Total: 2
wjw.test.mybatisplus.mapper.UserMapper.getList - [trace,143] - <==        Row: 2, ww, 2022-06-29, 陈大, 123456, 0, 2022-06-29 13:06:24.0, 2022-06-29 13:06:24.0
w.t.mybatisplus.mapper.RoleMapper.getListByUserId - [debug,137] - ====>  Preparing: select * from role left join user_role on role.id=user_role.role_id where user_role.user_id=?
w.t.mybatisplus.mapper.RoleMapper.getListByUserId - [debug,137] - ====> Parameters: 2(Integer)
w.t.mybatisplus.mapper.RoleMapper.getListByUserId - [trace,143] - <====    Columns: id, name, remark, user_id, role_id
w.t.mybatisplus.mapper.RoleMapper.getListByUserId - [trace,143] - <====        Row: 1, 系统管理员, 系统管理员, 2, 1
w.t.mybatisplus.mapper.RoleMapper.getListByUserId - [trace,143] - <====        Row: 2, 数据管理员, 数据管理员, 2, 2
w.t.mybatisplus.mapper.RoleMapper.getListByUserId - [debug,137] - <====      Total: 2
wjw.test.mybatisplus.mapper.UserMapper.getList - [debug,137] - <==      Total: 2
[UserVo [id=1, nick_Name=lh, username=李大, birthday=2022-06-29, roles=[Role [id=1, name=系统管理员, remark=系统管理员], Role [id=2, name=数据管理员, remark=数据管理员]]], UserVo [id=2, nick_Name=ww, username=陈大, birthday=2022-06-29, roles=[Role [id=1, name=系统管理员, remark=系统管理员], Role [id=2, name=数据管理员, remark=数据管理员]]]]

将user的id=1,id=2传入，得到结果如下：

[UserVo [id=1, nick_Name=lh, username=李大, birthday=2022-06-29, roles=[Role [id=1, name=系统管理员, remark=系统管理员], Role [id=2, name=数据管理员, remark=数据管理员]]], UserVo [id=2, nick_Name=ww, username=陈大, birthday=2022-06-29, roles=[Role [id=1, name=系统管理员, remark=系统管理员], Role [id=2, name=数据管理员, remark=数据管理员]]]]

可以看出表中id为1和2的user信息和其对应的角色信息都已经查询出来了。

如果传递多个参数呢?

如果select属性指定的方法需要多个参数,column的写法是这样的:column = "{查询参数1=主查询列名1, 查询参数2=主查询列名2}"

@Select({"select * from group where account_id=#{accountId} and delete_flag=0"})
@Results({@Result(property = "groupId", column = "group_id", id = true),
          @Result(property = "name", column = "user_name"), 
          @Result(property = "accountId", column = "account_id"),
          @Result(property = "deleteFlag", column = "delete_Flag"),
          @Result(property = "parentId", column = "parent_Id"), 
          @Result(property = "userList", many 
//"groupId=group_id",相当于将主查询中的列group_id映射到查询参数groupId中
//"userName=user_name",相当于将主查询中的列user_name映射到查询参数userName中
=@Many(select="selectUsersByGroupId"), column = "{groupId=group_id ,userName=user_name}")})
List<Group> selectGroupWithUsers(@Param("accountId") String accountId);
 
 
@Select({"select u.* from user u",
		"inner join user_group ug on u.user_id = ug.user_id",
		"where ug.group_id=#{groupId} and u.user_name=#{userName} and u.delete_flag=0"
		})
List<User> selectUsersByGroupId(@Param("groupId") String groupId, @Param("userName") String userName);