最近我在做一个不需要认证的项目，但是在做CRUD操作之前，我必须检查用户是否存在于数据库中。我用guard作为装饰器来解决这个问题。请找到下面的解决方案。

import { CanActivate, Injectable, ExecutionContext, NotFoundException } from '@nestjs/common';
import { Observable } from 'rxjs';
import { InjectModel } from '@nestjs/mongoose';
import { Model } from 'mongoose';
import { UserParamsNotFoundException } from 'src/statusResponse/error.response';

@Injectable()
export class UserGuard implements CanActivate {
    constructor(
        @InjectModel(Users.name) private userModel: Model<CreateUser>,
    ) {}
    async canActivate(
        context: ExecutionContext,
    ): Promise<any> {
        const request = context.switchToHttp().getRequest();

        const { user, } = request.body; // u can extract the key using object destructing .
        const isUserExist: boolean = function (); // which will return true or false;

        if (!isUserExist) throw new NotFoundException('Oops User not exist. Try again');
        else return true;
    }
};

希望这对你有帮助。