09—mybatis注解配置join查询

今天来聊mybatis的join查询，怎么说呢，有的时候，join查询确实能提升查询效率，今天举个left join的例子，来看看mybatis的join查询。

就不写的很细了，把主要代码贴出来了。

创建数据表：admin_user、admin_groups

CREATE TABLE `admin_user` (
  `id` bigint(20) NOT NULL AUTO_INCREMENT COMMENT '用户编号',
  `user_name` varchar(255) NOT NULL COMMENT '用户登录账号',
  `pwd` varchar(255) DEFAULT NULL COMMENT '登录密码',
  `create_date` datetime DEFAULT NULL COMMENT '创建时间',
  `enable_flag` int(20) DEFAULT NULL COMMENT '用户状态 0:可用 1:不可用',
  `group_id` int(20) DEFAULT NULL COMMENT '分组ID,0超级管理员,1一般管理员',
  `last_login_ip` varchar(255) DEFAULT NULL COMMENT '最后一次登录IP地址',
  `last_login_time` datetime DEFAULT NULL COMMENT '最后登录时间',
  `login_count` int(11) DEFAULT NULL,
  PRIMARY KEY (`id`),
  UNIQUE KEY `user_name` (`user_name`) USING BTREE
) 

---------------------------------------------------------------------------------
CREATE TABLE `admin_groups` (
  `id` int(11) NOT NULL AUTO_INCREMENT,
  `group_name` varchar(255) DEFAULT NULL,
  `create_by_user_name` varchar(255) DEFAULT NULL,
  `create_time` datetime DEFAULT NULL,
  `update_time` datetime DEFAULT NULL,
  `parent_id` int(11) DEFAULT NULL,
  `remarks` varchar(1000) NOT NULL DEFAULT '无' COMMENT '描述',
  `enable_flag` int(2) NOT NULL DEFAULT '1',
  PRIMARY KEY (`id`)
)

创建实体类：AdminUserJoinGroups.java

package com.palmble.entity;
import lombok.Data;
import javax.persistence.Table;

@Table(name = "admin_user")
@Data
public class AdminUserJoinGroups {
    private Long id;
    private String userName;
    private String groupName;
    private String createByUserName;
}

service层：AdminUserService.java

@Service
public class AdminUserService {

    @Autowired
    private AdminUserMapper adminUserMapper;
    public List<AdminUserJoinGroups> selectAllList()
    {
        return  adminUserMapper.selectAllList();
    }
}

mapper层：AdminUserMapper.java

@Mapper
public interface AdminUserMapper {

    @Select(" SELECT u.id,user_name,g.group_name,g.create_by_user_name FROM admin_user u left join admin_groups g on u.group_id=g.id;")
    @Results(id = "userGroupMap", value = {
            @Result(id = true, column = "id", property = "id"),
            @Result(column = "user_name", property = "userName"),
            @Result(column = "group_name", property = "groupName"),
            @Result(column = "create_by_user_name", property = "createByUserName")
    })
    List<AdminUserJoinGroups> selectAllList();
}

测试：

@RestController
@RequestMapping("/admin")
public class AdminController {
    @Autowired
    private AdminUserService adminUserService;

    @RequestMapping("/getUserGroup")
    public String getUserGroup() {
        List<AdminUserJoinGroups> adminUserJoinGroups = adminUserService.selectAllList();
        StringBuilder sb = new StringBuilder();
        for (AdminUserJoinGroups item : adminUserJoinGroups) {
            sb.append("id=" + item.getId() + ",username=" + item.getUserName() + ",groupname=" + item.getGroupName() + ",createByUserName=" + item.getCreateByUserName());
        }
        return sb.toString();
    }