通过在xml文件写sql的方式来实现一个接口 （22.11.19）

准备

在写接口之前要连接上数据库（用户名、密码要正确）

application.yml文件

server:
  port: 9999
spring:
  datasource:
    driver-class-name: com.mysql.cj.jdbc.Driver
    username: root
    password: root
    url: jdbc:mysql://localhost:3306/test?useUnicode=true&characterEncoding=utf-8&allowMultiQueries=true&useSSL=false&serverTimezone=GMT%2b8
    type: com.alibaba.druid.pool.DruidDataSource
#  jpa:
#    generate-ddl: false
#    hibernate:
#      ddl-auto: none
  servlet:
    multipart:
      max-file-size: 100MB
      max-request-size: 100MB

mybatis:
  mapper-locations: classpath:mapper/*.xml

logging:
  level:
    com:
      example:
        mapper:
          debug

sql文件：

/*
 Navicat Premium Data Transfer

 Source Server         : localhost_3306
 Source Server Type    : MySQL
 Source Server Version : 50721
 Source Host           : localhost:3306
 Source Schema         : x-admin

 Target Server Type    : MySQL
 Target Server Version : 50721
 File Encoding         : 65001

 Date: 27/06/2021 21:50:30
*/

SET NAMES utf8mb4;
SET FOREIGN_KEY_CHECKS = 0;

-- ----------------------------
-- Table structure for book
-- ----------------------------
DROP TABLE IF EXISTS `book`;
CREATE TABLE `book`  (
  `id` bigint(20) NOT NULL AUTO_INCREMENT COMMENT '序号',
  `name` varchar(255) CHARACTER SET utf8mb4 COLLATE utf8mb4_unicode_ci NULL DEFAULT NULL COMMENT '名称',
  `price` decimal(10, 2) NULL DEFAULT NULL COMMENT '价格',
  PRIMARY KEY (`id`) USING BTREE
) ENGINE = InnoDB AUTO_INCREMENT = 3 CHARACTER SET = utf8mb4 COLLATE = utf8mb4_unicode_ci ROW_FORMAT = Dynamic;

-- ----------------------------
-- Records of book
-- ----------------------------
INSERT INTO `book` VALUES (2, '1', 11.11);

-- ----------------------------
-- Table structure for t_log
-- ----------------------------
DROP TABLE IF EXISTS `t_log`;
CREATE TABLE `t_log`  (
  `id` bigint(20) NOT NULL AUTO_INCREMENT COMMENT '序号',
  `content` varchar(1000) CHARACTER SET utf8mb4 COLLATE utf8mb4_unicode_ci NULL DEFAULT NULL COMMENT '操作内容',
  `time` varchar(255) CHARACTER SET utf8mb4 COLLATE utf8mb4_unicode_ci NULL DEFAULT NULL COMMENT '操作时间',
  `user` varchar(255) CHARACTER SET utf8mb4 COLLATE utf8mb4_unicode_ci NULL DEFAULT NULL COMMENT '操作人',
  `ip` varchar(255) CHARACTER SET utf8mb4 COLLATE utf8mb4_unicode_ci NULL DEFAULT NULL COMMENT 'ip',
  PRIMARY KEY (`id`) USING BTREE
) ENGINE = InnoDB AUTO_INCREMENT = 132 CHARACTER SET = utf8mb4 COLLATE = utf8mb4_unicode_ci ROW_FORMAT = DYNAMIC;

-- ----------------------------
-- Records of t_log
-- ----------------------------
INSERT INTO `t_log` VALUES (80, '用户 admin 登录系统', '2021-05-25 16:42:07', 'admin', '0:0:0:0:0:0:0:1');
INSERT INTO `t_log` VALUES (81, '更新用户：admin ', '2021-05-25 16:42:19', 'admin', '0:0:0:0:0:0:0:1');
INSERT INTO `t_log` VALUES (82, '用户 admin 退出系统', '2021-05-25 16:42:29', 'admin', '0:0:0:0:0:0:0:1');
INSERT INTO `t_log` VALUES (83, '用户 admin 登录系统', '2021-05-25 16:42:31', 'admin', '0:0:0:0:0:0:0:1');
INSERT INTO `t_log` VALUES (84, '更新用户：jerry ', '2021-05-25 16:49:14', 'admin', '0:0:0:0:0:0:0:1');
INSERT INTO `t_log` VALUES (85, '用户 admin 登录系统', '2021-05-25 16:49:30', 'admin', '0:0:0:0:0:0:0:1');
INSERT INTO `t_log` VALUES (86, '用户 admin 登录系统', '2021-05-25 16:50:07', 'admin', '0:0:0:0:0:0:0:1');
INSERT INTO `t_log` VALUES (87, '更新用户：jerry ', '2021-05-25 16:50:21', 'admin', '0:0:0:0:0:0:0:1');
INSERT INTO `t_log` VALUES (88, '用户 admin 登录系统', '2021-05-26 16:35:40', 'admin', '0:0:0:0:0:0:0:1');
INSERT INTO `t_log` VALUES (89, '更新用户：jerry ', '2021-05-26 16:36:16', 'admin', '0:0:0:0:0:0:0:1');
INSERT INTO `t_log` VALUES (90, '更新用户：jack ', '2021-05-26 16:36:18', 'admin', '0:0:0:0:0:0:0:1');
INSERT INTO `t_log` VALUES (91, '删除用户 tom ', '2021-05-26 16:36:29', 'admin', '0:0:0:0:0:0:0:1');
INSERT INTO `t_log` VALUES (92, '删除用户 hello ', '2021-05-26 16:36:30', 'admin', '0:0:0:0:0:0:0:1');
INSERT INTO `t_log` VALUES (93, '删除用户 jack ', '2021-05-26 16:36:31', 'admin', '0:0:0:0:0:0:0:1');
INSERT INTO `t_log` VALUES (94, '删除用户 jerry ', '2021-05-26 16:36:32', 'admin', '0:0:0:0:0:0:0:1');
INSERT INTO `t_log` VALUES (95, '用户 admin 登录系统', '2021-05-31 12:18:16', 'admin', '0:0:0:0:0:0:0:1');
INSERT INTO `t_log` VALUES (96, '更新用户：admin ', '2021-05-31 12:19:48', 'admin', '0:0:0:0:0:0:0:1');
INSERT INTO `t_log` VALUES (97, '更新用户：admin ', '2021-05-31 12:19:57', 'admin', '0:0:0:0:0:0:0:1');
INSERT INTO `t_log` VALUES (98, '用户 admin 登录系统', '2021-06-01 16:46:09', 'admin', '0:0:0:0:0:0:0:1');
INSERT INTO `t_log` VALUES (99, '新增用户：zhang ', '2021-06-01 16:46:46', 'admin', '0:0:0:0:0:0:0:1');
INSERT INTO `t_log` VALUES (100, '新增用户：li ', '2021-06-01 16:47:12', 'admin', '0:0:0:0:0:0:0:1');
INSERT INTO `t_log` VALUES (101, '更新用户：admin ', '2021-06-01 16:47:19', 'admin', '0:0:0:0:0:0:0:1');
INSERT INTO `t_log` VALUES (102, '用户 admin 退出系统', '2021-06-01 16:47:22', 'admin', '0:0:0:0:0:0:0:1');
INSERT INTO `t_log` VALUES (103, '用户 admin 登录系统', '2021-06-01 16:47:24', 'admin', '0:0:0:0:0:0:0:1');
INSERT INTO `t_log` VALUES (104, '更新用户：li ', '2021-06-01 16:47:34', 'admin', '0:0:0:0:0:0:0:1');
INSERT INTO `t_log` VALUES (105, '更新用户：zhang ', '2021-06-01 16:47:35', 'admin', '0:0:0:0:0:0:0:1');
INSERT INTO `t_log` VALUES (106, '用户 admin 登录系统', '2021-06-07 12:32:17', 'admin', '0:0:0:0:0:0:0:1');
INSERT INTO `t_log` VALUES (107, '用户 admin 登录系统', '2021-06-07 14:16:00', 'admin', '0:0:0:0:0:0:0:1');
INSERT INTO `t_log` VALUES (108, '用户 admin 登录系统', '2021-06-07 14:34:26', 'admin', '0:0:0:0:0:0:0:1');
INSERT INTO `t_log` VALUES (109, '更新用户：li ', '2021-06-07 14:35:21', 'admin', '0:0:0:0:0:0:0:1');
INSERT INTO `t_log` VALUES (110, '更新用户：li ', '2021-06-07 14:35:23', 'admin', '0:0:0:0:0:0:0:1');
INSERT INTO `t_log` VALUES (111, '更新角色：超级管理员', '2021-06-07 14:35:41', 'admin', '0:0:0:0:0:0:0:1');
INSERT INTO `t_log` VALUES (112, '更新角色：超级管理员', '2021-06-07 14:35:45', 'admin', '0:0:0:0:0:0:0:1');
INSERT INTO `t_log` VALUES (113, '更新权限菜单：用户管理', '2021-06-07 14:37:58', 'admin', '0:0:0:0:0:0:0:1');
INSERT INTO `t_log` VALUES (114, '更新权限菜单：用户管理', '2021-06-07 14:38:08', 'admin', '0:0:0:0:0:0:0:1');
INSERT INTO `t_log` VALUES (115, '更新权限菜单：用户管理', '2021-06-07 14:38:13', 'admin', '0:0:0:0:0:0:0:1');
INSERT INTO `t_log` VALUES (116, '更新权限菜单：用户管理', '2021-06-07 14:38:21', 'admin', '0:0:0:0:0:0:0:1');
INSERT INTO `t_log` VALUES (117, '用户 admin 登录系统', '2021-06-07 14:57:29', 'admin', '0:0:0:0:0:0:0:1');
INSERT INTO `t_log` VALUES (118, '更新角色：超级管理员', '2021-06-07 14:57:43', 'admin', '0:0:0:0:0:0:0:1');
INSERT INTO `t_log` VALUES (119, '用户 admin 登录系统', '2021-06-09 23:19:38', 'admin', '0:0:0:0:0:0:0:1');
INSERT INTO `t_log` VALUES (120, '删除权限菜单：学生管理', '2021-06-09 23:19:50', 'admin', '0:0:0:0:0:0:0:1');
INSERT INTO `t_log` VALUES (121, '用户 admin 登录系统', '2021-06-12 10:18:54', 'admin', '0:0:0:0:0:0:0:1');
INSERT INTO `t_log` VALUES (122, '更新角色：超级管理员', '2021-06-12 10:30:15', 'admin', '0:0:0:0:0:0:0:1');
INSERT INTO `t_log` VALUES (123, '用户 admin 登录系统', '2021-06-12 13:55:01', 'admin', '0:0:0:0:0:0:0:1');
INSERT INTO `t_log` VALUES (124, '用户 admin 登录系统', '2021-06-27 10:44:12', 'admin', '0:0:0:0:0:0:0:1');
INSERT INTO `t_log` VALUES (125, '更新角色：超级管理员', '2021-06-27 10:44:26', 'admin', '0:0:0:0:0:0:0:1');
INSERT INTO `t_log` VALUES (126, '用户 admin 登录系统', '2021-06-27 11:15:11', 'admin', '0:0:0:0:0:0:0:1');
INSERT INTO `t_log` VALUES (127, '更新角色：超级管理员', '2021-06-27 11:15:17', 'admin', '0:0:0:0:0:0:0:1');
INSERT INTO `t_log` VALUES (128, '用户 admin 登录系统', '2021-06-27 11:18:36', 'admin', '0:0:0:0:0:0:0:1');
INSERT INTO `t_log` VALUES (129, '用户 admin 登录系统', '2021-06-27 11:41:59', 'admin', '0:0:0:0:0:0:0:1');
INSERT INTO `t_log` VALUES (130, '更新角色：超级管理员', '2021-06-27 11:42:04', 'admin', '0:0:0:0:0:0:0:1');
INSERT INTO `t_log` VALUES (131, '用户 admin 登录系统', '2021-06-27 11:49:27', 'admin', '0:0:0:0:0:0:0:1');

-- ----------------------------
-- Table structure for t_message
-- ----------------------------
DROP TABLE IF EXISTS `t_message`;
CREATE TABLE `t_message`  (
  `id` bigint(20) NOT NULL AUTO_INCREMENT COMMENT 'ID',
  `content` text CHARACTER SET utf8mb4 COLLATE utf8mb4_general_ci NULL COMMENT '内容',
  `username` varchar(255) CHARACTER SET utf8mb4 COLLATE utf8mb4_unicode_ci NULL DEFAULT NULL COMMENT '评论人',
  `time` varchar(255) CHARACTER SET utf8mb4 COLLATE utf8mb4_general_ci NULL DEFAULT NULL COMMENT '评论时间',
  `parent_id` bigint(20) NULL DEFAULT NULL COMMENT '父ID',
  `foreign_id` bigint(20) NULL DEFAULT 0 COMMENT '关联id',
  PRIMARY KEY (`id`) USING BTREE
) ENGINE = InnoDB AUTO_INCREMENT = 20 CHARACTER SET = utf8mb4 COLLATE = utf8mb4_unicode_ci COMMENT = '留言表' ROW_FORMAT = DYNAMIC;

-- ----------------------------
-- Records of t_message
-- ----------------------------
INSERT INTO `t_message` VALUES (16, '我来了', 'admin', '2021-04-23 23:15:57', NULL, 0);
INSERT INTO `t_message` VALUES (17, '来了老弟', 'admin', '2021-04-23 23:17:46', 16, 0);
INSERT INTO `t_message` VALUES (19, '今天直播', 'admin', '2021-04-24 11:08:41', 17, 0);

-- ----------------------------
-- Table structure for t_notice
-- ----------------------------
DROP TABLE IF EXISTS `t_notice`;
CREATE TABLE `t_notice`  (
  `id` bigint(20) NOT NULL AUTO_INCREMENT COMMENT 'ID',
  `title` varchar(255) CHARACTER SET utf8mb4 COLLATE utf8mb4_unicode_ci NULL DEFAULT NULL COMMENT '标题',
  `content` text CHARACTER SET utf8mb4 COLLATE utf8mb4_unicode_ci NULL COMMENT '内容',
  `time` varchar(255) CHARACTER SET utf8mb4 COLLATE utf8mb4_unicode_ci NULL DEFAULT NULL COMMENT '发布时间',
  PRIMARY KEY (`id`) USING BTREE
) ENGINE = InnoDB AUTO_INCREMENT = 7 CHARACTER SET = utf8mb4 COLLATE = utf8mb4_unicode_ci ROW_FORMAT = DYNAMIC;

-- ----------------------------
-- Records of t_notice
-- ----------------------------
INSERT INTO `t_notice` VALUES (4, '学习', '别问！问就是3连！', '2021-05-17 15:29:29');
INSERT INTO `t_notice` VALUES (5, '快乐是什么？', '快乐就是一杯咖啡，一个键盘，从早到晚', '2021-05-17 15:30:08');
INSERT INTO `t_notice` VALUES (6, 'Java是什么', 'Java是世界上最好的语言', '2021-05-17 15:30:42');

-- ----------------------------
-- Table structure for t_permission
-- ----------------------------
DROP TABLE IF EXISTS `t_permission`;
CREATE TABLE `t_permission`  (
  `id` bigint(20) NOT NULL AUTO_INCREMENT,
  `name` varchar(255) CHARACTER SET utf8 COLLATE utf8_general_ci NULL DEFAULT NULL COMMENT '名称',
  `description` varchar(255) CHARACTER SET utf8 COLLATE utf8_general_ci NULL DEFAULT NULL COMMENT '描述',
  `path` varchar(255) CHARACTER SET utf8 COLLATE utf8_general_ci NULL DEFAULT NULL COMMENT '菜单路径',
  `icon` varchar(255) CHARACTER SET utf8 COLLATE utf8_general_ci NULL DEFAULT 's-data' COMMENT '图标',
  PRIMARY KEY (`id`) USING BTREE
) ENGINE = InnoDB AUTO_INCREMENT = 32 CHARACTER SET = utf8 COLLATE = utf8_general_ci COMMENT = '权限菜单表' ROW_FORMAT = DYNAMIC;

-- ----------------------------
-- Records of t_permission
-- ----------------------------
INSERT INTO `t_permission` VALUES (1, '用户管理', '用户管理', 'user', 'user-solid');
INSERT INTO `t_permission` VALUES (2, '角色管理', '角色管理', 'role', 's-cooperation');
INSERT INTO `t_permission` VALUES (3, '权限管理', '权限管理', 'permission', 'menu');
INSERT INTO `t_permission` VALUES (19, '公告管理', '公告管理', 'notice', 'data-board');
INSERT INTO `t_permission` VALUES (24, '日志管理', '日志管理', 'log', 'notebook-2');
INSERT INTO `t_permission` VALUES (25, '在线留言', '在线留言', 'message', 'message');
INSERT INTO `t_permission` VALUES (31, '图书管理', '图书管理', 'book', 's-data');

-- ----------------------------
-- Table structure for t_role
-- ----------------------------
DROP TABLE IF EXISTS `t_role`;
CREATE TABLE `t_role`  (
  `id` bigint(20) NOT NULL AUTO_INCREMENT COMMENT 'ID',
  `name` varchar(255) CHARACTER SET utf8 COLLATE utf8_general_ci NULL DEFAULT NULL COMMENT '名称',
  `description` varchar(255) CHARACTER SET utf8 COLLATE utf8_general_ci NULL DEFAULT NULL COMMENT '描述',
  `permission` varchar(2000) CHARACTER SET utf8 COLLATE utf8_general_ci NULL DEFAULT NULL COMMENT '权限列表',
  PRIMARY KEY (`id`) USING BTREE
) ENGINE = InnoDB AUTO_INCREMENT = 3 CHARACTER SET = utf8 COLLATE = utf8_general_ci COMMENT = '角色表' ROW_FORMAT = DYNAMIC;

-- ----------------------------
-- Records of t_role
-- ----------------------------
INSERT INTO `t_role` VALUES (1, '超级管理员', '所有权限', '[1,2,3,19,27,30,31]');
INSERT INTO `t_role` VALUES (2, '普通用户', '部分权限', '[]');

-- ----------------------------
-- Table structure for t_user
-- ----------------------------
DROP TABLE IF EXISTS `t_user`;
CREATE TABLE `t_user`  (
  `id` bigint(20) NOT NULL AUTO_INCREMENT,
  `username` varchar(255) CHARACTER SET utf8mb4 COLLATE utf8mb4_unicode_ci NOT NULL COMMENT '用户名',
  `password` varchar(255) CHARACTER SET utf8mb4 COLLATE utf8mb4_unicode_ci NULL DEFAULT NULL COMMENT '密码',
  `nick_name` varchar(255) CHARACTER SET utf8mb4 COLLATE utf8mb4_unicode_ci NULL DEFAULT NULL COMMENT '昵称',
  `email` varchar(255) CHARACTER SET utf8mb4 COLLATE utf8mb4_unicode_ci NULL DEFAULT NULL COMMENT '邮箱',
  `phone` varchar(255) CHARACTER SET utf8mb4 COLLATE utf8mb4_unicode_ci NULL DEFAULT NULL COMMENT '手机号',
  `avatar` varchar(255) CHARACTER SET utf8mb4 COLLATE utf8mb4_unicode_ci NULL DEFAULT NULL COMMENT '头像',
  `role` varchar(255) CHARACTER SET utf8mb4 COLLATE utf8mb4_unicode_ci NULL DEFAULT NULL COMMENT '角色',
  `address` varchar(255) CHARACTER SET utf8mb4 COLLATE utf8mb4_unicode_ci NULL DEFAULT NULL COMMENT '地址',
  `age` int(11) NULL DEFAULT NULL COMMENT '年龄',
  PRIMARY KEY (`id`) USING BTREE
) ENGINE = InnoDB AUTO_INCREMENT = 4 CHARACTER SET = utf8mb4 COLLATE = utf8mb4_unicode_ci COMMENT = '用户表' ROW_FORMAT = DYNAMIC;

-- ----------------------------
-- Records of t_user
-- ----------------------------
INSERT INTO `t_user` VALUES (1, 'admin', 'admin', '管理员', '111124444', '13978786565', '1622537239707', '[1]', '北京', NULL);
INSERT INTO `t_user` VALUES (2, 'zhang', '123456', '张三', '[email protected]', '13089897878', NULL, '[2]', '北京', 24);
INSERT INTO `t_user` VALUES (3, 'li', '123456', '李四', '[email protected]', '13989897898', NULL, '[2]', '南京', 22);

SET FOREIGN_KEY_CHECKS = 1;

写好一个实体类、通用返回类
实体类：

package com.example.entity;

import com.baomidou.mybatisplus.annotation.IdType;
import com.baomidou.mybatisplus.annotation.TableId;
import com.baomidou.mybatisplus.annotation.TableName;
import com.baomidou.mybatisplus.extension.activerecord.Model;
import lombok.Data;

@Data
@TableName("t_permission")
public class Permission extends Model<Permission> {
    /**
      * 主键
      */
    @TableId(value = "id", type = IdType.AUTO)
    private Long id;

    private String name;

    private String path;

    private String description;

    private String icon;

}

通用返回类：

package com.example.common;

public class Result<T> {
    private String code;
    private String msg;
    private T data;

    public String getCode() {
        return code;
    }

    public void setCode(String code) {
        this.code = code;
    }

    public String getMsg() {
        return msg;
    }

    public void setMsg(String msg) {
        this.msg = msg;
    }

    public T getData() {
        return data;
    }

    public void setData(T data) {
        this.data = data;
    }

    public Result() {
    }

    public Result(T data) {
        this.data = data;
    }

    public static Result success() {
        Result result = new Result<>();
        result.setCode("0");
        result.setMsg("成功");
        return result;
    }

    public static <T> Result<T> success(T data) {
        Result<T> result = new Result<>(data);
        result.setCode("0");
        result.setMsg("成功");
        return result;
    }

    public static Result error(String code, String msg) {
        Result result = new Result();
        result.setCode(code);
        result.setMsg(msg);
        return result;
    }
}

一、在controller层写一个方法，请求路径

建立好controller、service、mapper层：

二、在service层实现这个方法

三、在Mapper层实现

四、在xml文件中写sql